This work was supported by the Department of Energy Bioenergy Technologies Office under Contract no. DE-AC36-08-GO28308. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

<ol>
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T., Bhan, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+and+site+evolution+of+molybdenum+carbide+catalysts+upon+exposure+to+oxygen.">Structure and site evolution of molybdenum carbide catalysts upon exposure to oxygen.</a> J Catal. 326, 82-91 (2015).</li><li>Lee, W. S., Kumar, A., Wang, Z. S., Bhan, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+Titration+and+Transient+Kinetic+Studies+of+Site+Requirements+in+Mo2C-Catalyzed+Vapor+Phase+Anisole+Hydrodeoxygenation.">Chemical Titration and Transient Kinetic Studies of Site Requirements in Mo2C-Catalyzed Vapor Phase Anisole Hydrodeoxygenation.</a> ACS Catal. 5 (7), 4104-4114 (2015).</li><li>Ren, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selective+Hydrodeoxygenation+of+Biomass-Derived+Oxygenates+to+Unsaturated+Hydrocarbons+using+Molybdenum+Carbide+Catalysts.">Selective Hydrodeoxygenation of Biomass-Derived Oxygenates to Unsaturated Hydrocarbons using Molybdenum Carbide Catalysts.</a> Chemsuschem. 6 (5), 798-801 (2013).</li><li>Grob, R. L., Kaiser, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Modern Practice of Gas Chromatography. , 403-460 (2004).</li><li>Guiochon Georges, L., Guillemin Claude, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Journal of Chromatography Library. 42, 563-586 (1988).</li><li>Guiochon Georges, L., Guillemin Claude, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Journal of Chromatography Library. 42, 587-627 (1988).</li><li>Guiochon Georges, L., Guillemin Claude, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Journal of Chromatography Library. 42, 629-659 (1988).</li><li>Guiochon Georges, L., Guillemin Claude, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Journal of Chromatography Library. 42, 661-687 (1988).</li><li>Baddour, F. G., Nash, C. P., Schaidle, J. A., Ruddy, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+&#945;-MoC1-x+Nanoparticles+with+a+Surface-Modified+SBA-15+Hard+Template:+Determination+of+Structure-Function+Relationships+in+Acetic+Acid+Deoxygenation.">Synthesis of &#945;-MoC1-x Nanoparticles with a Surface-Modified SBA-15 Hard Template: Determination of Structure-Function Relationships in Acetic Acid Deoxygenation.</a> Angew. Chem., Int. Ed. n/a-n/a. , (2016).</li><li>Habas, S. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Facile+Molecular+Precursor+Route+to+Metal+Phosphide+Nanoparticles+and+Their+Evaluation+as+Hydrodeoxygenation+Catalysts.">A Facile Molecular Precursor Route to Metal Phosphide Nanoparticles and Their Evaluation as Hydrodeoxygenation Catalysts.</a> Chem. 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The authors have nothing to disclose.

The TPRxn method is a powerful tool for screening of catalytic materials, providing information about the activity and selectivity of a catalyst as a function of reaction temperature. Other temperature-programmed methods such as TPD, TPO and TPR can provide information on the adsorption strength of reactants, number of adsorption sites, and appropriate catalyst pre-treatment procedures, but do not provide direct catalytic performance data. It is important to note that the TPRxn method detailed in this work does not measure steady-state reaction rates, and thus, reaction data may include the effects of catalyst stabilization, deactivation and transport limitations. However, TPRxn studies are often higher throughput than steady-state experiments, providing initial insight into catalyst activity and selectivity that can motivate and inform more rigorous future studies. While deoxygenation of acetic acid over molybdenum carbide catalysts under specific reaction conditions is detailed in this work, the TPRxn method is applicable to a broad range of reactant compounds (e.g., ethanol, methanol, crotonaldehyde), catalytic materials (e.g., zeolites, noble metals, metal oxides) and reaction conditions (e.g., reactant concentrations, pre-treatment procedures, pressures). With the system setup described in this work, limitations in reactant molecules studied are primarily the volatility (i.e., boiling point) of the reactant molecule and compatibility with the analytical equipment. For use in the saturator, the reactant must be volatile enough to achieve sufficient concentrations in the vapor phase as dictated by thermodynamic principles (i.e., vapor-liquid-equilibrium). The use of higher-boiling point compounds can be accomplished with the addition of a controlled heating device to the saturator, such as a heated mineral oil bath.
The ability to monitor the reactor effluent gas in real-time using the online MS allows the user to monitor reaction progress and to verify that the system is performing correctly, thus improving the efficiency of the TPRxn method. Use of the MS simplifies the system operation, as monitoring primary fragmentation peaks (Table 2) eliminates the guesswork in operations such as purge steps, in which it is important to know when the system is clear of contaminants that may affect the experiment. Although rigorous quantitative data is difficult to achieve from a MS, semi-quantitative data is attainable despite the complexity of observed product fragmentation patterns (Table 2). For optimal MS performance, it is critical to allow the turbo vacuum pump enough time to reach sufficiently low pressures at the ion source. Similarly, the 1 &#181;m orifice valve that controls gas flow to the MS must be firmly shut in order for the turbo pump to function properly between experiments (i.e., reach a sufficiently low pressure). The persistence of m/z = 18 (water) in MS data is one potential indicator that the turbo pump is not functioning properly or that more time is needed for the vacuum pump to purge the vacuum chamber prior to beginning an experiment.
An additional key to achieving reliable MS data is the collection of mass fragmentation patterns for relevant pure compounds prior to performing experiments. Mass fragmentation patterns are known to be instrument specific.29,30,31 If semi-quantitative data of reaction products is desired, collecting pure compound mass fragmentation patterns for each species, as shown in Table 2, will dramatically improve the quality and reliability of results. If semi-quantitative data is not needed, mass fragmentation patterns obtained from the NIST Chemistry WebBook database may suffice.28
Continuous monitoring of the MS ion source pressure and the system pressure during the reaction are important factors in troubleshooting any potential discrepancies in the data. In general, the system pressure positively affects the ion source pressure within the MS, and the ion source pressure directly affects the m/z signal intensity. Thus, changes in system pressure may lead to changes in MS signal intensity. An indication that this pressure effect was present during an experiment is a uniform increase in all m/z intensities. To mitigate this problem, ensure that the pressure drop across the reactor is low throughout the experiment. This can be achieved via dilution of the catalyst bed with quartz chips of the appropriate particle size as described in step 1.2.4.
A critical factor in achieving optimal quantitative performance of the &#181;GC is maintenance of instrument calibration data. Complete recalibration can be infrequent (i.e., annually or biannually); however, repeating a single standard calibration weekly will help to identify and correct any drift in the detector signal. Another phenomenon to be mindful of is retention time drift, particularly if chromatograms have peaks eluting near the end of the method (the shortest effective method run time is advantageous in maintaining high temporal resolution). Should retention times shift to later times, compound peaks may begin to decrease in area (due to backflush timing), or disappear altogether. Running sample calibration standards frequently will help identify this issue. An additional procedure that has improved the quality and reproducibility of our &#181;GC data is to hold the &#181;GC columns at their maximum allowable temperatures and pressures when the instrument is not in use (i.e., &#34;bakeout&#34; mode). This &#34;bakeout&#34; helps to remove oxygen, water, acetic acid and other contaminants from the &#181;GC columns and prepares the &#181;GC for the next experiment.
Various engineering controls have improved the overall functionality and performance of our acetic acid TPRxn system. A 2 &#181;m solids filter was placed upstream of the 1 &#181;m MS orifice. This filter has dramatically reduced the frequency of turbo pump shutdowns to manually clear blockage in the MS orifice. By reducing the frequency of orifice blockage, the solids filter has reduced the overall downtime of the system. Heat tapes are used on tubing sections to prevent vapors from condensing. This serves to protect the analytical equipment from damage and to maintain accurate analysis of the gas composition. Additionally, a small, unheated knockout vessel is located upstream of the &#181;GC. This knockout vessel (Figure 1D) is located at a low point in the system and serves as a redundant measure to reduce the possibility of liquid products entering the &#181;GC, which would cause damage to the columns. Clean gas filters are used on the &#181;GC carrier gases to remove any water and oxygen contaminants from the ultra-high purity (UHP) carrier gases. Water traps are also used on the H2 and UHP He gas feeds into the reactor system to prevent trace amounts of water from complicating the interpretation of experimental results.
Additional &#34;soft-use&#34; measures help to ensure collection of the highest quality data. For example, when using the &#181;GC the system pressure will increase from ambient to approximately 130 kPa. It is important to refrain from switching the three-way valve from its &#39;&#181;GC&#39; position to the &#39;local exhaust vent&#39; position while at a system pressure greater than 14 kPa, as the abrupt change in pressure will move the catalyst bed, pushing it into the system tubing. As a second example, diligent note taking will assist in data analysis and system troubleshooting, particularly notation of the system pressure and the temperature at which &#181;GC injections occur during the acetic acid TPRxn. The former is needed to calculate the actual flow rate of acetic acid across the catalyst bed (based on vapor-liquid-equilibrium principles), and the latter is important in accurately assigning &#181;GC data to a given temperature.

Temperature programmed reaction (TPRxn) is one of many temperature programmed methods, including desorption (TPD), oxidation (TPO), and reduction (TPR), and proceeds via exposure of a catalyst to a reactant concurrent with or followed by a steady increase in temperature.1,2,3 TPRxn is a transient technique that provides information about catalyst activity and selectivity as a function of reaction temperature.4,5,6 It is also a popular technique: a search of the keywords &#39;temperature programmed reaction&#39; in the literature yields over 1,000 sources citing its use.
TPRxn experiments are typically performed in a microreactor system, equipped with a mass spectrometer (MS) for real-time analysis of the reactor effluent and correlation of performance with temperature. Reactant gases can be introduced using mass flow controllers and liquids can be introduced via a syringe pump or as vapors by bubbling inert gas through a liquid. The catalyst is often pre-treated in situ to form the desired catalytic phase for the reaction. Some systems are equipped with additional analytical equipment, beyond the typical mass spectrometer, to provide quantitative or qualitative information about the catalyst selectivity, surface species present on the catalyst, or reaction mechanism. For example, temperature programmed in situ Fourier Transform Infrared Spectroscopy (FTIR) provides information about the evolution of surface species with varying reaction temperature.7,8 The TPRxn system demonstrated in this work is equipped with a gas chromatogram (GC) in addition to the more typical MS. This GC, equipped with four parallel columns, allows for more accurate quantification of the reaction products, but is limited in analysis frequency by the time it takes the products to elute through the columns. Thus, the combination of MS and GC can be particularly useful for coupling real-time identification with accurate quantification of reactants and products.
Here, we apply the TPRxn methodology to study the deoxygenation of acetic acid on molybdenum carbide catalysts. This is an interesting and important reaction in catalyst research, as acetic acid is a useful analog for the many carboxylic acids present in biomass pyrolysis vapors.9 The high oxygen content in biomass pyrolysis vapors necessitates oxygen removal to produce hydrocarbon fuels,10,11,12 and molybdenum carbide catalysts have shown promising deoxygenation performance for many biomass pyrolysis vapor model compounds, including furfural, 1-propanol, phenolics and acetic acid.9,13,14,15,16 However, the activity and selectivity of molybdenum carbide catalysts in deoxygenation reactions is dependent on the catalyst structure and composition, the reacting species and the reaction conditions.
The data collected from TPRxn of acetic acid shows that molybdenum carbide catalysts are active for deoxygenation reactions above ca. 300 &#176;C, and when combined with catalyst characterization information allows for quantification of the catalyst activity as a function of temperature via the calculation of acetic acid turnover rates. The TPRxn results show that deoxygenation (i.e., C-O bond-breaking) products are favored at temperatures below ca. 400 &#176;C and decarbonylation (i.e., C-C bond-breaking) products are favored at temperatures above ca. 400 &#176;C. Additionally, TPRxn studies illustrate the changes in the activity and selectivity of molybdenum carbide catalysts produced using various synthetic procedures (i.e., the production of different molybdenum carbide catalyst structures and compositions). Still, the value of this information and, more generally, the successful application of TPRxn experimental data toward catalyst design and process optimization is a function of the quality of the data obtained. Careful consideration and knowledge of the potential difficulties and limitations highlighted throughout the TPRxn procedure is paramount.

<table><tbody><tr><td>glacial acetic acid</td><td>Cole-Parmer</td><td>EW-88401-62</td><td>alternate supplier acceptable if ACS purity grade. See caution statement in protocol for safety information</td></tr><tr><td>UHP He</td><td>Airgas</td><td>HE R300SS</td><td>alternate supplier acceptable if&amp;nbsp;&gt;99.99% purity</td></tr><tr><td>UHP Ar</td><td>Arigas</td><td>AR R200</td><td>alternate supplier acceptable if&amp;nbsp;&gt;99.99% purity</td></tr><tr><td>acetone</td><td>VWR International</td><td>BDH1101-4LP</td><td>alternate supplier acceptable if&amp;nbsp;&gt;99.5% purity</td></tr><tr><td>quartz chips</td><td>Powder Technology Inc.</td><td>Crushed Quartz</td><td>sieved 180-300 &amp;micro;m, calcined in air at 500 &amp;deg;C overnight</td></tr><tr><td>mass spectrometer - turbo vacuum pump</td><td>Pfeiffer Vacuum</td><td>TSU 071</td><td>mass spectrometer is controlled with LabVIEW 2010 software package (National Instruments)</td></tr><tr><td>mass spectrometer - turbo vacuum pump</td><td>Stanford Research Systems</td><td>RGA100</td><td></td></tr><tr><td>micro gas chromatograph</td><td>Agilent</td><td>CP740388</td><td>490 Micro GC; 4-channel system&lt;br/&gt; Channel 1: 494001360 Molseive 10m, heated backflush&lt;br/&gt; Channel 2: 494001460 PPU 10m, heated backflush&lt;br/&gt; Channel 3: 490040 AL2O3/KCL 10+0.2m, heated backflush SPECIAL&lt;br/&gt; Channel 4: 492005750 5CB 15m, heated</td></tr><tr><td>GC software</td><td>Aglient</td><td>OpenLAB CDS EZChrom Edition</td><td></td></tr><tr><td>clean gas filters</td><td>Agilent</td><td>CP17974</td><td>for use on GC carrier gases (He, Ar)</td></tr><tr><td>quartz &quot;U-tube&quot; reactor</td><td>n/a</td><td></td><td>hand blown glass, custom built to order</td></tr><tr><td>bubbler</td><td>n/a</td><td></td><td>custom built to order</td></tr><tr><td>ceramic furnace</td><td>Watlow</td><td>discontinued</td><td>Similar furnace part #: VC401J12A-B000R</td></tr><tr><td>heat tape controller</td><td>n/a</td><td></td><td>custom built with Watlow EZ-zone parts</td></tr><tr><td>heat tape</td><td>Omega</td><td>FGH051-060</td><td>alternate supplier for extreme temperature heat tape acceptable</td></tr><tr><td>heat tape insulation</td><td>JEGS</td><td>710-80809</td><td>alternate supplier acceptable</td></tr><tr><td>thermocouple</td><td>Omega</td><td>&lt;em&gt;e.g.&lt;/em&gt;, KMQSS-062U-18</td><td>K-type thermocouples; alternate sizes may be required</td></tr><tr><td>thermocouple O-ring</td><td>Swagelok</td><td>VT-7-OR-001-1/2</td><td>perfluoroelastomer(fluorocarbon FKM) O-ring</td></tr><tr><td>2 &amp;micro;m solids filter, VCR gasket</td><td>Swagelok</td><td>SS-4-VCR-2-2M</td><td></td></tr><tr><td>1 &amp;micro;m orifice, VCR gasket</td><td>Lenox Laser</td><td>SS-4-VCR-2</td><td>for mass spectrometer orifice</td></tr><tr><td>316/316L stainless steel tubing and fittings</td><td>Swagelok</td><td>Varies</td><td>See Swagelok &#039;VCR Metal Gasket Face Seal Fittings&#039; and &#039;Stainless Steel Seamless Tubing and Tube Support Systems&#039; catalogs for more information</td></tr><tr><td>316/316L stainless steel tubing and fittings</td><td>Swagelok</td><td>Varies</td><td>See Swagelok &#039;Integral-Bonnet Needle Valves&#039;, &#039;Bellows-Sealed Valves&#039; and &#039;One-Piece Instrumentation Ball Valves&#039; catalogs for more information</td></tr></tbody></table>

temperature-programmed deoxygenation of acetic acid on molybdenum carbide catalysts

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system includes a reactor, furnace, gas and vapor sources, flow control, instrumentation to quantify reaction products (e.g., gas chromatograph), and instrumentation to monitor the reaction in real time (e.g., mass spectrometer). Here, we apply the TPRxn methodology to study molybdenum carbide catalysts for the deoxygenation of acetic acid, an important reaction among many in the upgrading/stabilization of biomass pyrolysis vapors. TPRxn is used to evaluate catalyst activity and selectivity and to test hypothetical reaction pathways (e.g., decarbonylation, ketonization, and hydrogenation). The results of the TPRxn study of acetic acid deoxygenation show that molybdenum carbide is an active catalyst for this reaction at temperatures above ca. 300 &#176;C and that the reaction favors deoxygenation (i.e., C-O bond-breaking) products at temperatures below ca. 400 &#176;C and decarbonylation (i.e., C-C bond-breaking) products at temperatures above ca. 400 &#176;C.

The online MS provides the capability to analyze the gas composition at the reactor outlet in real-time. The online MS is not coupled with any device to separate products prior to analysis, and thus species identification is challenging when differentiating between compounds with overlapping mass fragmentation patterns. As shown in Table 2, many of the common products from acetic acid TPRxn experiments are characterized by multiple common m/z signals. Deconvolution of the MS data (m/z = 1 - 100 as a function of temperature) allows for semi-quantitative data to be obtained because the MS signal intensity for a given species is roughly proportional to the partial pressure of that species.26,27 Following deconvolution, the data are normalized and corrected, and thus may be used semi-quantitatively to gather information such as reactant conversion and relative product concentration as a function of reaction temperature (Figure 4).
A &#181;GC is also included with the system for more accurate quantification of reactants and products, while maintaining the temporal resolution required for analyzing TPRxns. The &#181;GC method used by our group limits the frequency of sample collection to intervals of approximately 5.5 min (at a 10 &#176;C/min ramp rate, this corresponds to a sample approximately every 55 &#176;C). The time between samples is limited by the method required to achieve both carbon monoxide elution and separation between H2 and He in column 1 of the GC. Figures 5 and 6 show representative data for a study comparing the acetic acid deoxygenation activity and selectivity of molybdenum carbide catalysts with varying structures, morphologies and compositions. In that work, nanoparticle MoC1-x (NP-MoC1-x) were synthesized with and without an SBA-15 template and compared with bulk MoC1-x and bulk Mo2C. Figure 5 illustrates the use of &#181;GC data, combined with catalyst characterization information, to generate acetic acid (Figure 5A) and H2 (Figure 5B) turnover rates (TOR) as a function of reaction temperature. The results show that the templated NP-MoC1-x/mSBA demonstrated greater acetic acid TOR, and thus greater catalytic activity, compared to the untemplated NP-MoC1-x, and similar acetic acid TOR compared to the bulk molybdenum carbide catalysts below 400 &#176;C. Above 400 &#176;C, the templated catalyst demonstrated greater acetic acid TOR than any of the other catalysts studied. The H2 TOR was lower on the nanoparticle catalysts than on the bulk catalysts at all temperatures studied. Figures 6A and 6B show data for the reaction selectivity to decarbonylation and decarboxylation (DCO, sum of selectivities to CH4, CO2, and CO) and ketonization (KET, selectivity to acetone), respectively, as a function of reaction temperature obtained from &#181;GC sampling during TPRxn experiments. Both nanoparticle materials (NP-MoC1-x and NP-MoC1-x/mSBA) demonstrated higher selectivity to KET above 400 &#176;C than their bulk counterparts. In light of acid and H-site titration data, the authors concluded that the higher KET selectivity was attributed to an increase in the fraction of strong acid sites relative to the bulk materials. Furthermore, based on these results, the ratio of acid sites to H-sites was identified as a key property in determining acetic acid deoxygenation performance. In Figures 5 and 6, error bars for each data point are based on data collected for at least 3 replicate experiments.
<img alt="Figure 1" src="/files/ftp_upload/55314/55314fig1.jpg" /> 
Figure 1. TPRxn Equipment. (A) Wrapped heat tape. The heat tape is taped to the stainless tubing with high temperature electrical tape and covered with two layers of thermal insulation. (B) Acetic acid saturator. (C) Ceramic furnace. (D) Knockout vessel at low point in the TPRxn system upstream of the &#181;GC. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55314/55314fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55314/55314fig2.jpg" /> 
Figure 2. Quartz &#34;U-tube&#34; reactor. (A) Installed quartz &#34;U-tube&#34; reactor used for acetic acid TPRxn. (B) Close-up of molybdenum carbide catalyst bed and thermocouple. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55314/55314fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55314/55314fig3.jpg" /> 
Figure 3. Process flow diagram. The process flow diagram for the TPRxn system. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55314/55314fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/55314/55314fig4.jpg" /> 
Figure 4: Representative analysis of MS data after deconvolution. (A) Conversion of acetic acid and hydrogen and the (B and C) relative concentrations of products during acetic acid TPRxn using a molybdenum carbide catalyst. Reprinted with permission from [9]. Copyright 2016 American Chemical Society. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55314/55314fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/55314/55314fig5.jpg" /> 
Figure 5: Acetic acid and hydrogen turnover rate from &#181;GC data. The (A) acetic acid and (B) hydrogen turnover rate (TOR). The TOR values were calculated by normalizing acetic acid and hydrogen conversion by the number of acid- and H-sites, respectively, on the catalytic materials. Error bars were determined from at least 3 replicate experiments and represent the standard error in the data. Adapted with permission from [22]. Copyright 2016 Angewandte Chemie International Edition. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55314/55314fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/55314/55314fig6.jpg" /> 
Figure 6: Selectivity during acetic acid TPRxn experiments. The selectivity to (A) decarbonylation and decarboxylation (DCO) and (B) ketonization (KET) products during acetic acid TPRxn experiments over various molybdenum carbide catalysts. Error bars were determined from at least 3 replicate experiments and represent the standard error in the data. Adapted with permission from [22]. Copyright 2016 Angewandte Chemie International Edition. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55314/55314fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Table 1" src="/files/ftp_upload/55314/55314table1.jpg" /> 
Table 1: Reactant and product species with corresponding calibration concentrations. The typical concentration ranges for reactants and products during acetic acid TPRxn. Calibration standards for the &#181;GC should be designed to span the range of observed concentrations. 
Note: If a single concentration is shown, it may be assumed the lower range of the observed concentration range is 0 mol%.
<img alt="Table 2" src="/files/ftp_upload/55314/55314table2.jpg" /> 
Table 2: Mass fragmentation pattern. The fragmentation patterns of reactants and products during acetic acid TPRxn. Fragmentation patterns are used in the MS deconvolution algorithm to produce normalized species concentration data. Reprinted with permission from [9]. Copyright 2016 American Chemical Society. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55314/55314table2large.jpg" target="_blank">Please click here to view a larger version of this table.</a> 
aThe mass fragment intensities, highlighted in bold, have been identified as the primary mass fragments for each compound. 
bAll m/z values from 1 - 100 are collected during TPRxn experiments; only a selected subset is shown here corresponding to only those m/z values used in deconvolution. 
cMass fragmentation patterns are collected by introducing pure compound vapor into the MS for all compounds except ethane. The mass fragmentation pattern for ethane is obtained from the NIST Chemistry WebBook database.28

Watch this Scientific Journal Video about Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts at JoVE.com

Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts

Presented here is a protocol for the operation of a micro-scale temperature-programmed reactor for evaluating the catalytic performance of molybdenum carbide during acetic acid deoxygenation.

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system ...

temperature-programmed-deoxygenation-acetic-acid-on-molybdenum

Nanyang Technological University

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Thermodynamics and Chemical Kinetics

SCIENTISTS IN ACTION

11.4K Views.  National Renewable Energy Laboratory.  Hier gepresenteerd is een protocol voor de exploitatie van een micro-schaal-temperatuur geprogrammeerd reactor voor het evalueren van de katalytische prestaties van molybdeen carbide tijdens azijnzuur deoxygenatie. 

Video: Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts

Aerosol-assisted Chemical Vapor Deposition of Metal Oxide Structures: Zinc Oxide Rods

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, their high cost production and/or incompatibility with microfabrication technologies, due to the use of pre-deposited catalyst-seeds and/or high processing temperatures exceeding 900 &#176;C, represent a drawback for a widespread use of these methods. Here, however, we report the synthesis of ZnO rods via a non-catalyzed vapor-solid mechanism enabled by using an aerosol-assisted chemical vapor deposition (CVD) method at 400 &#176;C with zinc chloride (ZnCl2) as the precursor and ethanol as the carrier solvent. This method provides both single-step formation of ZnO rods and the possibility of their direct integration with various substrate types, including silicon, silicon-based micromachined platforms, quartz, or high heat resistant polymers. This potentially facilitates the use of this method at a large-scale, due to its compatibility with state-of-the-art microfabrication processes for device manufacture. This report also describes the properties of these structures (e.g., morphology, crystalline phase, optical band gap, chemical composition, electrical resistance) and validates its gas sensing functionality towards carbon monoxide.

Columnar zinc oxide structures in the form of rods are synthesized via aerosol-assisted chemical vapor deposition without the use of pre-deposited catalyst-seed particles. This method is scalable and compatible with various substrates based on either silicon, quartz or polymers.

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, ...

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental sciences and industrial applications owing to their periodic arrangement of nanopores with relatively high aspect ratio. However, the techniques reported so far, which could be only valid for mono-surface anodization, show critical disadvantages, i.e., time-consuming as well as complicated procedures, requiring toxic chemicals, and wasting valuable natural resources. In this paper, we demonstrate a facile, efficient, and environmentally clean method to fabricate nanoporous AAOs in sulfuric and oxalic acid electrolytes, which can overcome the limitations that result from conventional AAO fabricating methods. First, plural AAOs are produced at one time through simultaneous multi-surfaces anodization (SMSA), indicating mass-producibility of the AAOs with comparable qualities. Second, those AAOs can be separated from the aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs, implying simplicity and green technological characteristics. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, which reinforces the advantages of this strategy and also guarantees the efficient usage of natural resources.

A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental ...

Engineering

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity in aqueous CO2 reduction. Different from traditional metal nanocrystals, the synthesis of metal single atoms involves a matrix material that can confine those single atoms and prevent them from aggregation. We report an electrospinning and thermal annealing method to prepare Ni single atoms dispersed and coordinated in a graphene shell, as active centers for CO2 reduction to CO. During the synthesis, N dopants play a critical role in generating graphene vacancies to trap Ni atoms. Aberration-corrected scanning transmission electron microscopy and three-dimensional atom probe tomography were employed to identify the single Ni atomic sites in graphene vacancies. Detailed setup of electrochemical CO2 reduction apparatus coupled with an on-line gas chromatography is also demonstrated. Compared to metallic Ni, Ni single atom catalyst exhibit dramatically improved CO2 reduction and suppressed H2 evolution side reaction.

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Here, we present a protocol for the synthesis and electrochemical testing of transition metal single atoms coordinated in graphene vacancies as active centers for selective carbon dioxide reduction to carbon monoxide in aqueous solutions.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with wafer-scale uniformity and angstrom level control of thickness, the method of atomic-layer deposition was chosen. This ALD process enables high-quality, low-temperature (&#8804;150 &#176;C) growth of ultrathin films (100-1000 &#197;) of VO2. For this demonstration, the VO2 films were grown on sapphire substrates. This low temperature growth technique produces mostly amorphous VO2 films. A subsequent anneal in an ultra-high vacuum chamber with a pressure of 7x10-4 Pa of ultra-high purity (99.999%) oxygen produced oriented, polycrystalline VO2 films. The crystallinity, phase, and strain of the VO2 were determined by Raman spectroscopy and X-ray diffraction, while the stoichiometry and impurity levels were determined by X-ray photoelectron spectroscopy, and finally the morphology was determined by atomic force microscopy. These data demonstrate the high-quality of the films grown by this technique. A model was created to fit to the data for VO2 in its metallic and insulating phases in the near infrared spectral region. The permittivity and refractive index of the ALD VO2 agreed well with the other fabrication methods in its insulating phase, but showed a difference in its metallic state. Finally, the analysis of the films&#39; optical properties enabled the creation of a wavelength- and temperature-dependent model of the complex optical refractive index for developing VO2 as a tunable refractive index material.

Thin films (100-1000 &#197;) of vanadium dioxide (VO2) were created by atomic-layer deposition (ALD) on sapphire substrates. Following this, the optical properties were characterized through the metal-insulator transition of VO2. From the measured optical properties, a model was created to describe the tunable refractive index of VO2.

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with ...

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven effective in gas adsorption, separations, and catalysis. MOFs are most commonly synthesized as bulk powder, requiring additional processes to adhere them to functional devices and fabrics that risk decreasing the powder porosity and adsorption capacity. Here, we demonstrate a method of first coating fabrics with metal oxide films using atomic layer deposition (ALD). This process creates conformal films of controllable thickness on each fiber, while providing a more reactive surface for MOF nucleation. By submerging the ALD coated fabric in solution during solvothermal MOF synthesis, the MOFs create a conformal, well-adhered coating on the fibers, resulting in a MOF-functionalized fabric, without additional adhesion materials that may block MOF pores and functional sites. Here we demonstrate two solvothermal synthesis methods. First, we form a MIL-96(Al) layer on polypropylene fibers using synthetic conditions that convert the metal oxide to MOF. Using initial inorganic films of varying thicknesses, diffusion of the organic linker into the inorganic allows us to control the extent of MOF loading on the fabric. Second, we perform a solvothermal synthesis of UiO-66-NH2 in which the MOF nucleates on the conformal metal oxide coating on polyamide-6 (PA-6) fibers, thereby producing a uniform and conformal thin film of MOF on the fabric. The resulting materials can be directly incorporated into filter devices or protective clothing and eliminate the maladroit qualities of loose powder.

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks are effective in gas storage and heterogeneous catalysis, but typical synthesis methods result in loose powders that are difficult to incorporate into smart materials. We demonstrate a method of first coating fabrics with ALD metal oxides, resulting in conformal films of MOF on the fabrics during solvothermal synthesis.

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven ...

Achieving Moderate Pressures in Sealed Vessels Using Dry Ice As a Solid CO2 Source

Herein is presented a general strategy to perform reactions under mild to moderate CO2 pressures with dry ice. This technique obviates the need for specialized equipment to achieve modest pressures, and can even be used to achieve higher pressures in more specialized equipment and sturdier reaction vessels. At the end of the reaction, the vials can be easily depressurized by opening at room temperature. In the present example CO2 serves as both a putative directing group as well as a way to passivate amine substrates, thereby preventing oxidation during the organometallic reaction. In addition to being easily added, the directing group is also removed under vacuum, obviating the need for extensive purification to remove the directing group. This strategy allows the facile &#947;-C(sp3)-H arylation of aliphatic amines and has the potential to be applied to a variety of other amine-based reactions.

Achieving Moderate Pressures in Sealed Vessels Using Dry Ice As a Solid CO2 Source

Here we present a protocol for performing reactions in simple reaction vessels under low-to-moderate pressures of CO2. The reactions can be performed in a variety of vessels simply by administering the carbon dioxide in the form of dry ice, without the need for costly or elaborate equipment or set-ups.

Herein is presented a general strategy to perform reactions under mild to moderate CO2 pressures with dry ice. This technique obviates the need for ...

CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light

We demonstrate a method for the enhancement of CO2 photoreduction. As the driving force of a photocatalytic reaction is from solar light, the basic idea is to use concentration technology to raise the incident solar light intensity. Concentrating a large-area light onto a small area cannot only increase light intensity, but also reduce the catalyst amount, as well as the reactor volume, and increase the surface temperature. The concentration of light can be realized by different devices. In this manuscript, it is realized by a Fresnel lens. The light penetrates the lens and is concentrated on a disc-shaped catalyst. The results show that both the reaction rate and the total yield are efficiently increased. The method can be applied to most CO2 photoreduction catalysts, as well as to similar reactions with a low reaction rate at natural light.

CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light

We present a protocol for improving the performance of CO2 photoreduction to CH4 by heightening the incident light intensity via concentrating solar energy technology.

We demonstrate a method for the enhancement of CO2 photoreduction. As the driving force of a photocatalytic reaction is from solar light, the basic idea ...

Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics

A significant number of heterogeneously-catalyzed chemical processes occur under liquid conditions, but simulating catalyst function under such conditions is challenging when it is necessary to include the solvent molecules. The bond breaking and forming processes modeled in these systems necessitate the use of quantum chemical methods. Since molecules in the liquid phase are under constant thermal motion, simulations must also include configurational sampling. This means that multiple configurations of liquid molecules must be simulated for each catalytic species of interest. The goal of the protocol presented here is to generate and sample trajectories of configurations of liquid water molecules around catalytic species on flat transition metal surfaces in a way that balances chemical accuracy with computational expense. Specifically, force field molecular dynamics (FFMD) simulations are used to generate configurations of liquid molecules that can subsequently be used in quantum mechanics-based methods such as density functional theory or ab initio molecular dynamics. To illustrate this, in this manuscript, the protocol is used for catalytic intermediates that could be involved in the pathway for the decomposition of glycerol (C3H8O3). The structures that are generated using FFMD are modeled in DFT in order to estimate the enthalpies of solvation of the catalytic species and to identify how H2O molecules participate in catalytic decompositions.

The goal of the protocol presented here is to generate and sample trajectories of configurations of liquid water molecules around catalytic species on a flat transition metal surface. The sampled configurations can be used as starting structures in quantum mechanics-based methods.

A significant number of heterogeneously-catalyzed chemical processes occur under liquid conditions, but simulating catalyst function under such conditions ...

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid nanosheets, a series of Pt/xHMNO6/CNTs with different solid acid compositions (x = 5, 20 wt%; M = Nb, Ta; N = Mo, W) have been prepared by carbon nanotube pretreatment, protonic exchange, solid acid exfoliation, aggregation and finally Pt particles impregnation. The Pt/xHMNO6/CNTs are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and NH3-temperature programmed desorption. The study revealed that HNbWO6 nanosheets were attached on CNTs, with some edges of the nanosheets being bent in shape. The acid strength of the supported Pt catalysts increases in the following order: Pt/CNTs &#60; Pt/5HNbWO6/CNTs &#60; Pt/20HNbMoO6/CNTs &#60; Pt/20HNbWO6/CNTs &#60; Pt/20HTaWO6/CNTs. In addition, the catalytic hydroconversion of lignin-derived model compound: diphenyl ether using the synthesized Pt/20HNbWO6 catalyst has been investigated.

A protocol for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs is presented.

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid ...

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids with adsorbates. Vibrational spectra provide information on the chemical nature of adsorbed species and their structure. Thus, they are very useful for obtaining molecular level understanding of surface species. The IR spectrum of the sample itself gives some direct information about the material. General conclusions can be drawn concerning hydroxyl groups, some stable surface species and impurities. However, the spectrum of the sample is &#34;blind&#34; with respect to the presence of coordinatively unsaturated ions and gives rather poor information about the acidity of surface hydroxyls, species decisive for the adsorption and catalytic properties of the materials. Furthermore, no discrimination between bulk and surface species can be made. These problems are solved by the use of probe molecules, substances that interact specifically with the surface; the alteration of some spectral features of these molecules as a result of adsorption provides valuable information about the nature, properties, location, concentration, etc., of the surface sites.
The experimental protocol for in-situ IR studies of gas/sample interaction includes preparation of a sample pellet, activation of the material, initial spectral characterization through the analysis of the background spectra, characterization by probe molecules, and study of the interaction with a particular set of gas mixtures. In this paper we investigate a zirconium terephthalate metal organic framework, Zr6O4(OH)4(BDC)6 (BDC = benzene-1,4-dicarboxylate), namely UiO-66 (UiO refers to University of Oslo). The acid sites of the UiO-66 sample are determined by using CO and CD3CN as molecular probes. Furthermore, we have demonstrated that CO2 is adsorbed on basic sites exposed on dehydroxylated UiO-66. Introduction of water to the system produces hydroxyl groups acting as additional CO2 adsorption sites. As a result, CO2 adsorption capacity of the sample is strongly enhanced.

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

The use of FTIR spectroscopy for investigation of the surface properties of polycrystalline solids is described. Preparation of sample pellets, activation procedures, characterization with probe molecules and model studies of CO2 adsorption are discussed.

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids ...

Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts

Samenvatting

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