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Effects of dopants on the properties of Cu/ZrO2 catalysts for methanol synthesis and steam reforming.

机译：掺杂剂对用于甲醇合成和蒸汽重整的Cu / ZrO2催化剂性能的影响。

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The influences of dopants (Ce, Mn, Pr) on the surface properties and catalytic performance of Cu/ZrO2 catalysts for CO hydrogenation to methanol have been investigated to determine the key parameters in designing active methanol synthesis catalysts. Selected methanol synthesis catalysts have been also screened for their activity in steam reforming of methanol. Steady-state activity tests were supplemented with XRD, infrared (IR) and Raman spectroscopies, temperature-programmed reduction (TPR) and desorption (TPD) catalysts characterization studies. The nature and relative dynamics of formation and consumption of surface species were examined using in-situ infrared spectroscopy. The mechanism for methanol synthesis from CO on Cu/CexZr1-xO2 catalysts has been proposed based on the results of dynamics studies.; Surface properties, activity and selectivity for methanol synthesis from CO/H2 on Cu/MxZr1-xO2 (M = Ce, Mn, Pr) were found to be highly dependent on the catalyst composition. The direct correlation between H2 adsorption capacity and methanol synthesis activity has been established. The results of IR-spectroscopy studies indicated that H2 is stored in the form of hydroxyl groups formed upon reduction of the catalyst in H2. Infrared spectroscopy results indicated that CO adsorption on each material leads to the formation of bidentate formate species through interaction with a hydroxyl group on the surface of MxZr1-xO2. The formate species are hydrogenated to methoxide species by hydrogen provided by Cu via spillover. The elimination of methoxide species by reaction with acidic OH groups is the rate-limiting step for methanol synthesis on each catalyst. The relative rates of elimination of methoxide species are faster for catalysts with higher concentration of more highly acidic bridging hydroxyl groups. The methanol synthesis activity per unit of surface area was highest for 3wt% Cu/Ce0.5Zr0.5 O2 catalyst which exhibits highest H2 storage capacity and relative concentration of more highly Bronsted acidic bridging hydroxyl groups.; The steam reforming of methanol to H2 was investigated for a series of Cu/MxZr1-xO2 (M = Ce, Mn, and Pr) catalysts. The most active catalysts were Cu/Ce0.5Zr0.5 O2 and Cu/Mn0.3Zr0.7O2. At 548 K rates of H2 production approaching 400 mmol H2·g-cat -1·h-1 were achieved with 3wt% Cu/Mn0.3 Zr0.7O2 catalyst. CO was observed to form via the reverse-water-gas-shift reaction, particularly at high methanol conversions and reaction temperatures. Formation of this byproduct could be suppressed by increasing the loading of Cu and increasing the H2O:CH 3OH ratio in the feed. Catalyst deactivation appears due to deposition of carbon on the surface of the catalyst. The extent of catalyst deactivation can be decreased significantly by increasing the Cu loading of the catalyst and the H2O:CH3OH ratio in the feed.
机译：研究了掺杂剂（Ce，Mn，Pr）对Cu / ZrO2催化剂进行CO加氢制甲醇的表面性能和催化性能的影响，从而确定了设计活性甲醇合成催化剂的关键参数。还已经筛选了选定的甲醇合成催化剂在甲醇蒸汽重整中的活性。通过XRD，红外（IR）和拉曼光谱，程序升温还原（TPR）和解吸（TPD）催化剂表征研究补充稳态活动测试。使用原位红外光谱技术检查了表面物质形成和消耗的性质和相对动力学。基于动力学研究的结果，提出了在Cu / CexZr1-xO2催化剂上由CO合成甲醇的机理。发现在Cu / MxZr1-xO2（M = Ce，Mn，Pr）上由CO / H2合成甲醇的表面性质，活性和选择性在很大程度上取决于催化剂的组成。已经建立了H 2吸附能力与甲醇合成活性之间的直接关系。红外光谱研究的结果表明，H 2以在H 2中还原催化剂时形成的羟基形式存储。红外光谱结果表明，CO在每种材料上的吸附通过与MxZr1-xO2表面的羟基相互作用而导致形成二齿甲酸盐。铜通过溢出提供的氢将甲酸类氢化为甲醇盐类。通过与酸性OH基反应来消除甲醇盐是在每种催化剂上合成甲醇的限速步骤。对于具有更高浓度的更强酸性桥连羟基的催化剂而言，甲醇盐种类的相对消除速率更快。 3wt％的Cu / Ce0.5Zr0.5O2催化剂的单位表面积的甲醇合成活性最高，该催化剂具有最高的H2储存能力和更高浓度的布朗斯台德酸性桥连羟基的相对浓度。对于一系列Cu / MxZr1-xO2（M = Ce，Mn和Pr）催化剂，研究了将甲醇蒸汽重整为H2的方法。活性最高的催化剂是Cu / Ce0.5Zr0.5 O2和Cu / Mn0.3Zr0.7O2。使用3wt％的Cu / Mn0.3 Zr0.7O2催化剂，在548 K的氢气生成速率下可达到400 mmol H2·g-cat -1·h-1。观察到通过逆水煤气变换反应形成了CO，特别是在高甲醇转化率和反应温度下。副产物的形成可以通过增加进料中Cu的含量和增加H2O：CH 3OH的比例来抑制。由于碳在催化剂表面上的沉积而出现催化剂失活。催化剂失活的程度可以通过增加催化剂的铜载量和进料中H2O：CH3OH的比例来大大降低。

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