Crystal plane effect of ceria on supported copper catalyst for liquidphase hydrogenation of unsaturated aldehyde

Ceria has been widely used as catalyst support displaying a size- or shape-dependent catalytic performance due to the strong metal-support interaction (SMSI) effect with active metal. Almost all the studies on the SMSI effect of ceria-supported metal catalysts are involved generally in gas-phase reaction, but rarely in the liquid-phase reaction system. In this work, Cu/CeO2-P (copper loaded on nano-polyhedral CeO2 with (1 1 1) terminated surface) was investigated its catalytic performance on liquid-phase hydrogenation and studied the SMSI effect by comparing with the catalysts supported on nano-rod and nanocube CeO2. It was found that Cu was highly dispersed on the external surface of ceria in the Cu/CeO2-P catalyst via a moderate SMSI effect. Furthermore, the degree of the interaction showed great inflfluence on the chemical state of Cu species, and the ratio of (Cu+ +Cu0 )/Cu2+ in Cu/CeO2-P was higher than Cu/ CeO2-R (Cu loaded on nano-rod CeO2 with (1 1 0) plane) and Cu/CeO2-C (Cu loaded on nano-cube CeO2 with (1 0 0) facet). As a result, the Cu/CeO2-P catalyst showed the best catalytic performance among three types of catalysts. Based on series of catalytic investigations, the catalytic performance in liquid-phase hydrogenation was intrinsically relevant to the crystal plane effect and reduced Cu proportion induced by an appropriate SMSI effect, which was completely different from gas-phase hydrogenation.

二氧化铈（Ceria）作为催化剂载体被广泛应用，其与活性金属之间存在强金属-载体相互作用（Strong Metal-Support Interaction，SMSI）效应，因此催化性能呈现出尺寸或形貌依赖性。目前针对二氧化铈负载型金属催化剂的强金属-载体相互作用的研究，几乎均集中于气相反应体系，而液相反应体系中的相关研究则较为稀缺。本工作以Cu/CeO₂-P（负载于暴露(111)晶面的纳米多面体CeO₂上的铜基催化剂）为研究对象，考察其在液相加氢反应中的催化性能，并分别与负载于纳米棒状CeO₂与纳米立方状CeO₂的催化剂进行对比，以探究其强金属-载体相互作用效应。研究发现，在适度的强金属-载体相互作用下，Cu在Cu/CeO₂-P催化剂的二氧化铈外表面实现了高度分散。进一步研究表明，该相互作用的强度对铜物种的化学状态具有显著调控作用：Cu/CeO₂-P中(Cu⁺ + Cu⁰)/Cu²⁺的比例高于Cu/CeO₂-R（负载于暴露(110)晶面的纳米棒状CeO₂上的铜基催化剂）与Cu/CeO₂-C（负载于暴露(100)晶面的纳米立方状CeO₂上的铜基催化剂）。最终，Cu/CeO₂-P催化剂在三类催化剂中展现出最优的催化性能。基于一系列催化表征与性能测试结果，该液相加氢反应的催化性能本质上与晶面效应以及适度强金属-载体相互作用诱导的铜物种还原比例密切相关，这一作用机制与气相加氢反应完全不同。