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Synthesis Gas Conversion over Rh-Mn-WxC/SiO2 Catalysts Prepared by Atomic Layer Deposition
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-10-11 00:00:00 , DOI: 10.1021/acscatal.8b02461 Yifei Liu 1 , Lifeng Zhang 1 , Florian Göltl 1 , Madelyn R. Ball 1 , Ive Hermans 1, 2 , Thomas F. Kuech 1 , Manos Mavrikakis 1 , James A. Dumesic 1
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-10-11 00:00:00 , DOI: 10.1021/acscatal.8b02461 Yifei Liu 1 , Lifeng Zhang 1 , Florian Göltl 1 , Madelyn R. Ball 1 , Ive Hermans 1, 2 , Thomas F. Kuech 1 , Manos Mavrikakis 1 , James A. Dumesic 1
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The catalytic conversion of synthesis gas to value-added oxygenates and light hydrocarbons was studied on Rh and Rh–Mn clusters on tungsten carbide-overcoated silica (WxC/SiO2) at 523 K, 580 psi, and CO/H2 = 1/1. The WxC-modified SiO2 support was prepared by the overcoating of WOx on SiO2 using atomic layer deposition (ALD) followed by carburization. The reactivities of Rh/WxC/SiO2 catalysts with varying number of ALD cycles (number of cycles = 2, 5, 10, 20, and 30) were measured and showed that 5 ALD cycles of WxC suppressed the formation of methane. All WxC-modified catalysts showed enhancement in selectivity toward methanol and ethanol through CO hydrogenation and acetaldehyde hydrogenation, respectively. These catalysts also improved the overall turnover frequency (TOF). The addition of Mn species further promoted the activity and the selectivity toward ethanol and C2+ hydrocarbons, especially light alkenes. The best performing Rh-2Mn/5cycle-WxC/SiO2 catalyst (Rh:Mn molar ratio = 1:2) achieved 84.7% selectivity toward valuable oxygenates and C2+ hydrocarbons with a ratio of alkenes to alkanes equal to 1.7, compared to Rh/SiO2 which exhibited 80.4% selectivity toward the products aforementioned with a ratio of 0.5. The overall TOF was 20 times higher than that over Rh/SiO2 (i.e., 5.6 × 10–2 s–1 vs 2.9 × 10–3 s–1). X-ray diffraction revealed that the existence of W2C, which was the dominant phase in Rh/5cycle-WxC/SiO2, favored the suppression of methane and enhanced the production of alcohols and C2+ hydrocarbons compared to the WC support. Density functional theory calculations for Rh19, Rh31, and Rh37 clusters on various WC surfaces suggested that the shape of Rh clusters is condition dependent and subject to H2 pressure. The C- and O- binding energies on various sites for the clusters were used with scaling relations to probe their catalytic activity. With the use of this approach, the increase in the O binding energy when moving from the SiO2-supported Rh37 cluster to the WC-supported cluster leads to an increase in the activity of Rh/WxC/SiO2 at the expense of the reduction in the number of sites that are selective toward C2 oxygenates.
中文翻译：
原子层沉积制备的Rh-Mn-W x C / SiO 2催化剂上的合成气转化
合成气的增值含氧化合物和轻质烃类的催化转化研究在Rh和Rh-Mn系簇上碳化钨-外涂二氧化硅（W X C /的SiO 2在523 K，580磅，和CO）/ H 2 = 1/1。W x C改性的SiO 2载体是通过使用原子层沉积（ALD）在SiO 2上覆盖WO x并随后进行渗碳制备的。铑的反应性/ W X C /的SiO 2层的催化剂与不同数量的ALD循环的测定，并表明，W的5个ALD循环（= 2，5，10，20，和30个循环的数目）X C禁止的形成甲烷。全部W xC改性的催化剂分别通过CO加氢和乙醛加氢显示出对甲醇和乙醇的选择性增强。这些催化剂还改善了总周转频率（TOF）。Mn物种的添加进一步提高了对乙醇和C 2+烃，特别是轻质烯烃的活性和选择性。性能最佳的Rh-2Mn / 5cycle-W x C / SiO 2催化剂（Rh：Mn摩尔比= 1：2）对有价值的含氧化合物和C 2+烃的选择性为84.7％，且烯烃与烷烃之比等于1.7，与Rh / SiO 2相比其对上述产物的选择性为80.4％，比率为0.5。总体TOF是Rh / SiO 2的20倍（即5.6×10 –2 s –1与2.9×10 –3 s –1）。X射线衍射表明，与WC相比，存在于Rh / 5cycle-W x C / SiO 2中的主导相W 2 C有利于抑制甲烷并提高了醇和C 2+碳氢化合物的产量。支持。Rh 19，Rh 31和Rh 37的密度泛函理论计算不同的WC表面上的团簇表明Rh团簇的形状取决于条件并受H 2压力的影响。在簇的各个位置上的C-和O-结合能与比例关系被用来探测它们的催化活性。通过使用该方法的，在将O的增加从在SiO移动时结合能2 -支持的Rh 37中的Rh的活性/ W簇的WC-支持的群集导致增加X C /的SiO 2牺牲对C 2含氧化合物有选择性的位点数量减少的原因。
更新日期：2018-10-11
中文翻译：
原子层沉积制备的Rh-Mn-W x C / SiO 2催化剂上的合成气转化
合成气的增值含氧化合物和轻质烃类的催化转化研究在Rh和Rh-Mn系簇上碳化钨-外涂二氧化硅（W X C /的SiO 2在523 K，580磅，和CO）/ H 2 = 1/1。W x C改性的SiO 2载体是通过使用原子层沉积（ALD）在SiO 2上覆盖WO x并随后进行渗碳制备的。铑的反应性/ W X C /的SiO 2层的催化剂与不同数量的ALD循环的测定，并表明，W的5个ALD循环（= 2，5，10，20，和30个循环的数目）X C禁止的形成甲烷。全部W xC改性的催化剂分别通过CO加氢和乙醛加氢显示出对甲醇和乙醇的选择性增强。这些催化剂还改善了总周转频率（TOF）。Mn物种的添加进一步提高了对乙醇和C 2+烃，特别是轻质烯烃的活性和选择性。性能最佳的Rh-2Mn / 5cycle-W x C / SiO 2催化剂（Rh：Mn摩尔比= 1：2）对有价值的含氧化合物和C 2+烃的选择性为84.7％，且烯烃与烷烃之比等于1.7，与Rh / SiO 2相比其对上述产物的选择性为80.4％，比率为0.5。总体TOF是Rh / SiO 2的20倍（即5.6×10 –2 s –1与2.9×10 –3 s –1）。X射线衍射表明，与WC相比，存在于Rh / 5cycle-W x C / SiO 2中的主导相W 2 C有利于抑制甲烷并提高了醇和C 2+碳氢化合物的产量。支持。Rh 19，Rh 31和Rh 37的密度泛函理论计算不同的WC表面上的团簇表明Rh团簇的形状取决于条件并受H 2压力的影响。在簇的各个位置上的C-和O-结合能与比例关系被用来探测它们的催化活性。通过使用该方法的，在将O的增加从在SiO移动时结合能2 -支持的Rh 37中的Rh的活性/ W簇的WC-支持的群集导致增加X C /的SiO 2牺牲对C 2含氧化合物有选择性的位点数量减少的原因。
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