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Synthesis Gas Conversion Over Molybdenum-Based Catalysts Promoted by Transition Metals

机译：通过过渡金属促进基于钼的催化剂的合成气转化

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摘要

Catalysts consisting of transition metals (Ni, Co, Cu, and Ru) supported on molybdenum oxide synthesized by atomic layer deposition (ALD) on silica were studied for synthesis gas conversion at 523 K and a pressure of 580 psi. Transition-metal-promoted Mo-based catalysts (M/MoO3/SiO2) showed different selectivity patterns from the transition metal supported on silica (M/SiO2). All molybdenum-based catalysts displayed a similar selectivity pattern, consisting of 15-20% of CH4, 30-40% of C2+ hydrocarbons, and 35-40% of oxygenates. The addition of transition metals to molybdenum oxide promoted the catalytic activity by an order of magnitude. Temperature program reduction indicated hydrogen spillover from the transition metals to molybdenum species. H-2-D-2 exchange rate measurements showed that the addition of the transition metal enhanced the rate of H-2 dissociation on the catalyst. CO chemisorption measurements indicated that transition-metal-promoted molybdenum catalysts consist of a similar amount of strong adsorption sites, which may originate from the reduced transition metal, and weak adsorption sites, which may originate from reduced molybdenum oxides. A dual-site mechanism is suggested in which low-valent molybdenum species dissociate CO and generate CHx groups that are hydrogenated to hydrocarbons or react with adsorbed CO on higher-valent Mo sites to form higher alcohols. Ni, Co, and Ru are able to generate CHx groups and enhance the production of C2+ oxygenates, whereas all of the transition metals studied are able to provide sites for H-2 dissociation and H spillover to molybdenum oxide, leading to further enhancement in catalytic activity compared to MoOx/SiO2.
机译：研究由二氧化硅上由原子层沉积（ALD）合成的氧化钼的过渡金属（Ni，Co，Cu和Ru）组成的催化剂，用于在523k和580psi的压力下进行合成气转化。过渡金属促进的基于MO的催化剂（M / MOO3 / SiO 2）显示了来自二氧化硅（M / SiO 2）上负载的过渡金属的不同选择性模式。所有钼的催化剂显示出类似的选择性模式，由15-20％的CH 4，30-40％的C 2 +烃和35-40％的含氧化合物组成。将过渡金属加入氧化钼的过渡金属通过幅度促进催化活性。温度减少将氢溢出从过渡金属向钼物种。 H-2-D-2汇率测量显示，加入过渡金属增强了催化剂上的H-2离解的速率。 CO化学吸附测量表明，过渡金属促进的钼催化剂由类似量的强吸附位点组成，其可以源于还原的过渡金属和弱的吸附位点，其可能来自氧化钼的还原物。提出了一种双位点机制，其中低价钼物种解离CO并产生氢化烃的CHX基团，或者在高价莫位点上与吸附的CO反应以形成高级醇。 Ni，Co和Ru能够产生CHX基团并增强C2 +含氧化合物的产生，而研究的所有过渡金属都能够为H-2解离和H溢出到氧化钼的所有过渡金属提供，导致催化剂进一步增强与Moox / SiO2相比的活动。

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