对碳化钼催化合成乙酸的程序升温脱氧
Summary
这里提出为微观尺度程序升温反应器用于在醋酸脱氧评估碳化钼的催化性能的操作的协议。
Abstract
程序升温反应（TPRxn）是在各种环境条件下筛分固体催化剂性能的一个简单而强大的工具。一个TPRxn系统包括一个反应器，炉，气体和蒸气源，流量控制，仪表量化的反应产物（ 例如 ，气相色谱仪），和仪器，以实时监控（ 例如 ，质谱仪）的反应。这里，我们应用TPRxn方法来研究碳化钼催化剂的乙酸，以及许多在生物质热解蒸气的升级/稳定的重要反应的脱氧。 TPRxn用于评估催化剂的活性和选择性，并测试假想反应途径（ 例如 ，脱羰基，ketonization，和氢化）。乙酸脱氧的TPRxn研究的结果表明，钼碳化物为在温度高于约该反应的活性催化剂300℃，并且反应主张脱氧（ 即 ，CO键破）产品在温度低于约 400°C和脱羰基（ 即 ，CC键破）产品在温度高于约 400℃。
Introduction
程序升温反应（TPRxn）是许多程序升温方法，包括解吸（TPD），氧化（TPO）和还原（TPR），并且进行经由催化剂与反应物的并发的曝光或随后在一个稳定增加1温度。 1，2，3 TPRxn是一个短暂的技术，该技术提供了有关催化剂的活性和选择性反应温度的函数的信息。 4，5，6，也是一个流行的技术：搜索文献亩产量达1000余源援引其使用关键字“程序升温反应'的。
TPRxn实验在微反应器系统典型地执行的，配备有质谱仪（MS），用于将反应器流出物的实时分析和p的相关性erformance温度。反应气体可以通过质量流量控制器和液体可以通过注射泵或通过液体鼓泡惰性气体的蒸气被引入引入。该催化剂通常是在原位预处理以形成用于该反应所需的催化阶段。一些系统配有附加的分析设备，超出了典型质谱仪，以提供有关该催化剂选择性存在于催化剂中，或反应机理的定量或定性的信息，表面的种类。例如，变换原位傅立叶编程的温度红外光谱（FTIR）提供了有关表面物种具有不同反应温度演变信息。 7,8在这项工作中表现出的TPRxn系统配备除更典型的MS的气相色谱（GC）。这GC，配备了四个平行柱，使得更精确的量化反应产物的fication，但在分析频率所花费的产品通过柱以洗脱时间的限制。因此，MS和GC的组合可以是用于与反应物和产物的准确定量耦合实时识别特别有用。
这里，我们应用TPRxn方法来研究乙酸对碳化钼催化剂的脱氧。这是催化剂研究的一个有趣和重要的反应，醋酸是存在于生物质热解蒸气许多羧酸一个有用的模拟。 9在生物质热解蒸气的高氧含量就必须除氧以产生烃燃料，10，11，12和碳化钼催化剂显示有前途的许多生物质热解蒸气模型化合物，包括糠醛，1-丙醇脱氧性能，酚和乙酸。 9，13，14，15，16然而，在脱氧反应的碳化钼催化剂的活性和选择性取决于催化剂的结构和组成，反应物质和反应条件。
从乙酸TPRxn收集的数据表明，碳化钼催化剂活性为上述约脱氧反应300℃，并且当带催化剂的表征信息相结合允许经由乙酸流动率的计算温度的函数的催化剂活性的定量。该TPRxn结果表明，脱氧（ 即 ，CO键破）产品在温度低于约青睐400°C和脱羰基（ 即 ，CC键破）产品FAVO红色在温度高于约 400℃。此外，TPRxn研究示出了使用各种合成方法生产碳化钼催化剂在活动的变化和选择性（ 即 ，生产不同碳化钼催化剂的结构和组合物）。尽管如此，这些信息的值，并且更一般的TPRxn实验数据朝向催化剂设计和工艺优化的成功应用是所得到的数据的质量的函数。在整个过程TPRxn强调了潜在的困难和局限性慎重考虑和知识是至关重要的。
Protocol
Representative Results
Discussion
该TPRxn方法为催化材料的筛选的有力工具，提供关于催化剂作为反应温度的函数的活性和选择性的信息。其他程序升温方法如TPD，TPO和TPR可以提供反应物的吸附力，吸附位点的数量，和适当的催化剂的前处理过程的信息，但不提供直接的催化性能数据。要注意，在这一工作中详述的TPRxn方法不测量稳态的反应速率，因此，反应数据可包括催化剂稳定化，失活和运输限制的影响是重要的。然而，TPRxn?…
Divulgaciones
The authors have nothing to disclose.
Acknowledgements
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.
Materials
| glacial acetic acid | Cole-Parmer | EW-88401-62 | alternate supplier acceptable if ACS purity grade. See caution statement in protocol for safety information |
| UHP H₂ | Airgas | HY R300 | alternate supplier acceptable if >99.99% purity |
| UHP He | Airgas | HE R300SS | alternate supplier acceptable if >99.99% purity |
| UHP Ar | Arigas | AR R200 | alternate supplier acceptable if >99.99% purity |
| acetone | VWR International | BDH1101-4LP | alternate supplier acceptable if >99.5% purity |
| quartz chips | Powder Technology Inc. | Crushed Quartz | sieved 180-300 µm, calcined in air at 500 °C overnight |
| mass spectrometer – turbo vacuum pump | Pfeiffer Vacuum | TSU 071 | mass spectrometer is controlled with LabVIEW 2010 software package (National Instruments) |
| mass spectrometer – turbo vacuum pump | Stanford Research Systems | RGA100 | |
| micro gas chromatograph | Agilent | CP740388 | 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 |
| GC software | Aglient | OpenLAB CDS EZChrom Edition | |
| clean gas filters | Agilent | CP17974 | for use on GC carrier gases (He, Ar) |
| quartz "U-tube" reactor | n/a | hand blown glass, custom built to order | |
| bubbler | n/a | custom built to order | |
| ceramic furnace | Watlow | discontinued | Similar furnace part #: VC401J12A-B000R |
| heat tape controller | n/a | custom built with Watlow EZ-zone parts | |
| heat tape | Omega | FGH051-060 | alternate supplier for extreme temperature heat tape acceptable |
| heat tape insulation | JEGS | 710-80809 | alternate supplier acceptable |
| thermocouple | Omega | e.g., KMQSS-062U-18 | K-type thermocouples; alternate sizes may be required |
| thermocouple o-ring | Swagelok | VT-7-OR-001-1/2 | perfluoroelastomer(fluorocarbon FKM) o-ring |
| 2 µm solids filter, VCR gasket | Swagelok | SS-4-VCR-2-2M | |
| 1 µm orifice, VCR gasket | Lenox Laser | SS-4-VCR-2 | for mass spectrometer orifice |
| 316/316L stainless steel tubing and fittings | Swagelok | Varies | See Swagelok 'VCR Metal Gasket Face Seal Fittings' and 'Stainless Steel Seamless Tubing and Tube Support Systems' catalogs for more information |
| 316/316L stainless steel tubing and fittings | Swagelok | Varies | See Swagelok 'Integral-Bonnet Needle Valves', 'Bellows-Sealed Valves' and 'One-Piece Instrumentation Ball Valves' catalogs for more information |
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