Ehinger Christian, Pollitt Stephan, De Jesus Silva Jordan, Zhou Xiaoyu, Sakamoto Kazutaka, Nachtegaal Maarten, Safonova Olga, Copéret Christophe
D-CHAB, ETH Zürich Vladimir-Prelog-Weg 2 8093 Zürich Switzerland
Center for Energy and Environmental Sciences, PSI Forschungsstrasse 111 5232 Villigen Switzerland
Chem Sci. 2025 Mar 5;16(14):5887-5896. doi: 10.1039/d4sc08532a. eCollection 2025 Apr 2.
Bimetallic heterogeneous catalysts combining group 9 metals (Rh, Ir) or group 10 metals (Ni, Pd, Pt) with Mo on a silica-based support have been synthesized surface organometallic chemistry and assessed in their catalytic activity for the hydrodeoxygenation (HDO) of alcohols with particular emphasis on the structural evolution of the catalysts and the role of Mo. The investigation was conducted with an air-free approach to isolate any sample alterations exclusively to those caused by the reaction. Structural analysis was performed using a combination of (S)TEM, IR, and XAS. It was found that Ir-Mo/SiO, Rh-Mo/SiO, and Pt-Mo/SiO display high activity for primary, secondary, and tertiary alcohol deoxygenation, while Pd-Mo/SiO selectively catalyses tertiary alcohol deoxygenation. Other combinations as well as the corresponding monometallic materials do not display the same activity. X-ray absorption spectroscopy confirmed metallic states for M (M = Ni, Rh, Pd, Ir, or Pt), while Mo K-edge XANES showed varying amounts of Mo(0), Mo(iv) and Mo(vi) depending on the metal counterpart in fresh materials, and indicated complete conversion of Mo(vi) to lower oxidation states (IV and 0) during the reaction. For Rh, Pd, Ir, and Pt, alloy formation (M-Mo) was identified M-Mo paths in EXAFS and supported by CO-IR spectroscopy. In contrast to Ir, Rh, and Pt, where some Mo(0) is present at the nanoparticle surface, Pd-Mo forms an alloy but likely retains Mo in the nanoparticle core, as suggested by CO-IR spectroscopy and CO-chemisorption. Reactivity studies suggest that tertiary alcohols primarily undergo dehydration-hydrogenation, evidenced by olefin formation with MoO /SiO, as well as Ir/SiO and Ir-Mo/SiO under inert conditions. In contrast, primary and secondary alcohols follow a different mechanism, correlated with the presence of metallic Mo species on the nanoparticle surface, highlighting their role in C-O bond activation. These findings provide new insights into the structure-activity relationships of Mo-based bimetallic catalysts, underscoring the influence of Mo in different oxidation states and strong substrate dependence on mechanistic pathways.
已通过表面有机金属化学合成了在二氧化硅基载体上结合第9族金属（铑、铱）或第10族金属（镍、钯、铂）与钼的双金属多相催化剂，并评估了它们对醇类加氢脱氧（HDO）的催化活性，特别强调了催化剂的结构演变和钼的作用。该研究采用无空气方法进行，以将任何样品变化仅隔离为由反应引起的那些变化。使用（S）TEM、IR和XAS的组合进行结构分析。发现Ir-Mo/SiO、Rh-Mo/SiO和Pt-Mo/SiO对伯醇、仲醇和叔醇脱氧表现出高活性，而Pd-Mo/SiO选择性催化叔醇脱氧。其他组合以及相应的单金属材料没有表现出相同的活性。X射线吸收光谱证实了M（M = 镍、铑、钯、铱或铂）的金属态，而钼K边XANES显示，取决于新鲜材料中的金属对应物，钼（0）、钼（IV）和钼（VI）的含量各不相同，并表明在反应过程中钼（VI）完全转化为较低氧化态（IV和0）。对于铑、钯、铱和铂，在EXAFS中确定了合金形成（M-Mo），并得到了CO-IR光谱的支持。与铱、铑和铂不同，在纳米颗粒表面存在一些钼（0），钯-钼形成合金，但如CO-IR光谱和CO化学吸附所表明的，可能在纳米颗粒核心中保留钼。反应性研究表明，叔醇主要经历脱水-氢化，在惰性条件下与MoO /SiO以及Ir/SiO和Ir-Mo/SiO形成烯烃证明了这一点。相比之下，伯醇和仲醇遵循不同的机制，这与纳米颗粒表面金属钼物种的存在相关，突出了它们在C-O键活化中的作用。这些发现为钼基双金属催化剂的构效关系提供了新的见解，强调了不同氧化态的钼的影响以及底物对机理途径的强烈依赖性。
