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. 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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 border="0" cellpadding="0" cellspacing="0" width="942">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">glacial acetic acid</td>
			<td style="width:179px;">Cole-Parmer</td>
			<td style="width:148px;">EW-88401-62</td>
			<td style="width:401px;">alternate supplier acceptable if ACS purity grade. See caution statement in protocol for safety information</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">UHP H&#8322;</td>
			<td style="width:179px;">Airgas</td>
			<td style="width:148px;">HY R300</td>
			<td>alternate supplier acceptable if &#62;99.99% purity</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">UHP He</td>
			<td style="width:179px;">Airgas</td>
			<td style="width:148px;">HE R300SS</td>
			<td>alternate supplier acceptable if &#62;99.99% purity</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">UHP Ar</td>
			<td style="width:179px;">Arigas</td>
			<td style="width:148px;">AR R200</td>
			<td>alternate supplier acceptable if &#62;99.99% purity</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">acetone</td>
			<td style="width:179px;">VWR International</td>
			<td style="width:148px;">BDH1101-4LP</td>
			<td>alternate supplier acceptable if &#62;99.5% purity</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">quartz chips</td>
			<td style="width:179px;">Powder Technology Inc.</td>
			<td style="width:148px;">Crushed Quartz</td>
			<td style="width:401px;">sieved 180-300 &#181;m, calcined in air at 500 &#176;C overnight</td>
		</tr>
		<tr height="56">
			<td height="56" style="height:56px;width:215px;">mass spectrometer - turbo vacuum pump</td>
			<td style="width:179px;">Pfeiffer Vacuum</td>
			<td style="width:148px;">TSU 071</td>
			<td style="width:401px;">mass spectrometer is controlled with LabVIEW 2010 software package (National Instruments)</td>
		</tr>
		<tr height="56">
			<td height="56" style="height:56px;width:215px;">mass spectrometer - turbo vacuum pump</td>
			<td style="width:179px;">Stanford Research Systems</td>
			<td style="width:148px;">RGA100</td>
			<td style="width:401px;"></td>
		</tr>
		<tr height="126">
			<td height="126" style="height:126px;width:215px;">micro gas chromatograph</td>
			<td style="width:179px;">Agilent</td>
			<td style="width:148px;">CP740388</td>
			<td style="width:401px;">490 Micro GC; 4-channel system 
			Channel 1: 494001360 Molseive 10m, heated backflush 
			Channel 2: 494001460 PPU 10m, heated backflush 
			Channel 3: 490040 AL2O3/KCL 10+0.2m, heated backflush SPECIAL 
			Channel 4: 492005750 5CB 15m, heated</td>
		</tr>
		<tr height="56">
			<td height="56" style="height:56px;width:215px;">GC software</td>
			<td style="width:179px;">Aglient</td>
			<td style="width:148px;">OpenLAB CDS EZChrom Edition</td>
			<td style="width:401px;"></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">clean gas filters</td>
			<td style="width:179px;">Agilent</td>
			<td style="width:148px;">CP17974</td>
			<td>for use on GC carrier gases (He, Ar)</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">quartz &#34;U-tube&#34; reactor</td>
			<td style="width:179px;">n/a</td>
			<td style="width:148px;"></td>
			<td>hand blown glass, custom built to order</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">bubbler</td>
			<td style="width:179px;">n/a</td>
			<td style="width:148px;"></td>
			<td>custom built to order</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">ceramic furnace</td>
			<td style="width:179px;">Watlow</td>
			<td style="width:148px;">discontinued</td>
			<td>Similar furnace part #: VC401J12A-B000R</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">heat tape controller</td>
			<td style="width:179px;">n/a</td>
			<td style="width:148px;"></td>
			<td>custom built with Watlow EZ-zone parts</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">heat tape</td>
			<td style="width:179px;">Omega</td>
			<td style="width:148px;">FGH051-060</td>
			<td style="width:401px;">alternate supplier for extreme temperature heat tape acceptable</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">heat tape insulation</td>
			<td style="width:179px;">JEGS</td>
			<td style="width:148px;">710-80809</td>
			<td>alternate supplier acceptable</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">thermocouple</td>
			<td style="width:179px;">Omega</td>
			<td style="width:148px;">e.g., KMQSS-062U-18</td>
			<td>K-type thermocouples; alternate sizes may be required</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">thermocouple o-ring</td>
			<td style="width:179px;">Swagelok</td>
			<td style="width:148px;">VT-7-OR-001-1/2</td>
			<td>perfluoroelastomer(fluorocarbon FKM) o-ring</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">2 &#181;m solids filter, VCR gasket</td>
			<td style="width:179px;">Swagelok</td>
			<td style="width:148px;">SS-4-VCR-2-2M</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">1 &#181;m orifice, VCR gasket</td>
			<td style="width:179px;">Lenox Laser</td>
			<td style="width:148px;">SS-4-VCR-2</td>
			<td>for mass spectrometer orifice</td>
		</tr>
		<tr height="93">
			<td height="93" style="height:94px;width:215px;">316/316L stainless steel tubing and fittings</td>
			<td style="width:179px;">Swagelok</td>
			<td style="width:148px;">Varies</td>
			<td style="width:401px;">See Swagelok &#39;VCR Metal Gasket Face Seal Fittings&#39; and &#39;Stainless Steel Seamless Tubing and Tube Support Systems&#39; catalogs for more information</td>
		</tr>
		<tr height="93">
			<td height="93" style="height:94px;width:215px;">316/316L stainless steel tubing and fittings</td>
			<td style="width:179px;">Swagelok</td>
			<td style="width:148px;">Varies</td>
			<td style="width:401px;">See Swagelok &#39;Integral-Bonnet Needle Valves&#39;, &#39;Bellows-Sealed Valves&#39; and &#39;One-Piece Instrumentation Ball Valves&#39; 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 ...

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11.3K Views.  National Renewable Energy Laboratory. 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.

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

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle diameters ranging from 30-250 nm by varying the reaction conditions. Through the selection of a microwave compatible solvent, silicic acid precursor, catalyst, and microwave irradiation time, these microwave-assisted methods were capable of overcoming the previously reported shortcomings associated with synthesis of silica nanoparticles using microwave reactors. The siloxane precursor was hydrolyzed using the acid catalyst, HCl. Acetone, a low-tan &#948; solvent, mediates the condensation reactions and has minimal interaction with the electromagnetic field. Condensation reactions begin when the silicic acid precursor couples with the microwave radiation, leading to silica nanoparticle sol formation. The silica nanoparticles were characterized by dynamic light scattering data and scanning electron microscopy, which show the materials&#39; morphology and size to be dependent on the reaction conditions. Microwave-assisted reactions produce silica nanoparticles with roughened textured surfaces that are atypical for silica sols produced by St&#246;ber&#39;s methods, which have smooth surfaces.

Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

Manufacturing of Three-dimensionally Microstructured Nanocomposites through Microfluidic Infiltration

Microstructured composite beams reinforced with complex three-dimensionally (3D) patterned nanocomposite microfilaments are fabricated via nanocomposite in&#64257;ltration of 3D interconnected microfluidic networks. The manufacturing of the reinforced beams begins with the fabrication of microfluidic networks, which involves layer-by-layer deposition of fugitive ink filaments using a dispensing robot, filling the empty space between filaments using a low viscosity resin, curing the resin and finally removing the ink.&#160;Self-supported 3D structures with other geometries and many layers (e.g.&#160;a few hundreds layers) could be built using this method. The resulting tubular micro&#64258;uidic networks are then infiltrated with thermosetting nanocomposite suspensions containing nanofillers (e.g.&#160;single-walled carbon nanotubes), and subsequently cured. The infiltration is done by applying a pressure gradient between two ends of the empty network (either by applying a vacuum or vacuum-assisted microinjection). Prior to the infiltration, the nanocomposite suspensions are prepared by dispersing nanofillers into polymer matrices using ultrasonication and three-roll mixing methods. The nanocomposites (i.e.&#160;materials infiltrated) are then solidified under UV exposure/heat cure, resulting in a 3D-reinforced composite structure. The technique presented here enables the design of functional nanocomposite macroscopic products for microengineering applications such as actuators and sensors.

Three-dimensional (3D) microstructured composite beams are fabricated through the directed and localized infiltration of nanocomposites into 3D porous microfluidic networks. The flexibility of this manufacturing method enables the utilization of different thermosetting materials and nanofillers in order to achieve a variety of functional 3D reinforced nanocomposite macroscopic products.

Microstructured composite beams reinforced with complex three-dimensionally (3D) patterned nanocomposite microfilaments are fabricated via nanocomposite ...

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

Dynamic Electrochemical Measurement of Chloride Ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

Extraction and Purification of Polyphenols from Freeze-dried Berry Powder for the Treatment of Vascular Smooth Muscle Cells In Vitro

Epidemiological studies indicate that increased flavonoid intake correlates with decreased mortality due to cardiovascular diseases (CVD) in the United States (US) and Europe. Berries are widely consumed in the US and have a high polyphenolic content. Polyphenols have been shown to interact with many molecular targets and to exert numerous positive biological functions, including antioxidant, anti-inflammatory, and cardioprotective effects. Polyphenols isolated from blackberry (BL), raspberry (RB), and black raspberry (BRB) reduce oxidative stress and cellular senescence in response to angiotensin II (Ang II). This work provides a detailed description of the protocol used to prepare the polyphenol extracts from freeze-dried berries. Polyphenol extractions from freeze-dried berry powder were performed using 80% aqueous ethanol and an ultrasonic-assisted extraction method. The crude extract was further purified and fractionated using chloroform and ethyl acetate, respectively. The effects of both crude and purified extracts were tested on Vascular Smooth Muscle Cells (VSMCs) in culture.

Extraction and Purification of Polyphenols from Freeze-dried Berry Powder for the Treatment of Vascular Smooth Muscle Cells In Vitro

This work details a step-by-step method to prepare polyphenol-rich extracts from freeze-dried berry powder. In addition, it provides a thorough description of how to use these polyphenol-rich extracts in cell culture in the presence of the peptide hormone angiotensin II (Ang II) using Vascular Smooth Muscle Cells (VSMCs).

Epidemiological studies indicate that increased flavonoid intake correlates with decreased mortality due to cardiovascular diseases (CVD) in the United ...

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are demonstrated here. The catalyst forms a substitutional solid solution structure, with a small and uniform particle size around 2 nm. This is realized by careful control over the impregnation, calcination, and reduction steps during catalyst preparation and is identified by advanced in situ synchrotron techniques. The catalyst propane dehydrogenation performance continuously improves with increasing Cu:Pt atomic ratio.

A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are ...

Synthesis of High Purity Nonsymmetric Dialkylphosphinic Acid Extractants

We present the synthesis of (2,3-dimethylbutyl)(2,4,4&#39;-trimethylpentyl)phosphinic acid as an example to demonstrate a method for the synthesis of high purity nonsymmetric dialkylphosphinic acid extractants. Low toxic sodium hypophosphite was chosen as the phosphorus source to react with olefin A (2,3-dimethyl-1-butene) to generate a monoalkylphosphinic acid intermediate. Amantadine was adopted to remove the dialkylphosphinic acid byproduct, as only the monoalkylphosphinic acid can react with amantadine to form an amantadine&#8729;mono-alkylphosphinic acid salt, while the dialkylphosphinic acid cannot react with amantadine due to its large steric hindrance. The purified monoalkylphosphinic acid was then reacted with olefin B (diisobutylene) to yield nonsymmetric dialkylphosphinic acid (NSDAPA). The unreacted monoalkylphosphinic acid can be easily removed by a simple base-acid post-treatment and other organic impurities can be separated out through the precipitation of the cobalt salt. The structure of the (2,3-dimethylbutyl)(2,4,4&#39;-trimethylpentyl)phosphinic acid was confirmed by 31P NMR, 1H NMR, ESI-MS, and FT-IR. The purity was determined by a potentiometric titration method, and the results indicate that the purity can exceed 96%.

A protocol for the synthesis of high purity nonsymmetric dialkylphosphinic acid extractants is presented, taking (2,3-dimethylbutyl)(2,4,4&#39;-trimethylpentyl)phosphinic acid as an example.

We present the synthesis of (2,3-dimethylbutyl)(2,4,4&#39;-trimethylpentyl)phosphinic acid as an example to demonstrate a method for the synthesis of high ...

Continuous Flow Chemistry: Reaction of Diphenyldiazomethane with p-Nitrobenzoic Acid

Continuous flow technology has been identified as instrumental for its environmental and economic advantages leveraging superior mixing, heat transfer and cost savings through the &#34;scaling out&#34; strategy as opposed to the traditional &#34;scaling up&#34;. Herein, we report the reaction of diphenyldiazomethane with p-nitrobenzoic acid in both batch and flow modes. To effectively transfer the reaction from batch to flow mode, it is essential to first conduct the reaction in batch. As a consequence, the reaction of diphenyldiazomethane was first studied in batch as a function of temperature, reaction time, and concentration to obtain kinetic information and process parameters. The glass flow reactor set-up is described and combines two types of reaction modules with &#34;mixing&#34; and &#34;linear&#34; microstructures. Finally, the reaction of diphenyldiazomethane with p-nitrobenzoic acid was successfully conducted in the flow reactor, with up to 95% conversion of the diphenyldiazomethane in 11 min. This proof of concept reaction aims to provide insight for scientists to consider flow technology&#39;s competitiveness, sustainability, and versatility in their research.

Continuous Flow Chemistry: Reaction of Diphenyldiazomethane with p-Nitrobenzoic Acid

Flow chemistry carries environmental and economic advantages by leveraging superior mixing, heat transfer and cost benefits. Herein, we provide a blueprint to transfer chemical processes from batch to flow mode. The reaction of diphenyldiazomethane (DDM) with p-nitrobenzoic acid, conducted in batch and flow, was chosen for proof of concept.

Continuous flow technology has been identified as instrumental for its environmental and economic advantages leveraging superior mixing, heat transfer and ...

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of NixNb1-xO nanoparticles with different atomic compositions (x = 0.03, 0.08, 0.15, and 0.20) have been prepared by chemical precipitation. These NixNb1-xO catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The study revealed the sponge-like and fold-like appearance of Ni0.97Nb0.03O and Ni0.92Nb0.08O on the NiO surface, and the larger surface area of these NixNb1-xO catalysts, compared with the bulk NiO. Maximum surface area of 173 m2/g can be obtained for Ni0.92Nb0.08O catalysts. In addition, the catalytic hydroconversion of lignin-derived compounds using the synthesized Ni0.92Nb0.08O catalysts have been investigated.

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

A protocol for the synthesis of sponge-like and fold-like Ni1-xNbxO nanoparticles by chemical precipitation is presented.

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

Preparation of Polyoxometalate-based Photo-responsive Membranes for the Photo-activation of Manganese Oxide Catalysts

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic polymers, with the aim of photo-activating oxygen-evolving manganese oxide catalysts, which are important components in artificial photosynthesis. The cross-linking technique was applied to obtain a self-standing membrane with a high PW12O403- content. Incorporation and structure retention of PW12O403- within the polymer matrix were confirmed by FT-IR and micro-Raman spectroscopy, and optical characteristics were investigated by UV-Vis spectroscopy, which revealed successful construction of the metal-to-metal charge transfer (MMCT) unit. After deposition of MnOx oxygen evolving catalysts, photocurrent measurements under visible light irradiation verified the sequential charge transfer, Mn &#8594; MMCT unit &#8594; electrode, and&#160;the photocurrent intensity was consistent with the redox potential of the donor metal (Ce or Co). This method provides a new strategy for preparing integrated systems involving catalysts and photon-absorption parts for use with photo-functional materials.

Here, we present a protocol to prepare charge transfer chromophores based on a polyoxometalate/polymer composite membrane.

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic ...