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Selectivity tuning over monometallic and bimetallic dehydrogenation catalysts: effects of support and particle size

机译:选择性优化单本位制的和双金属:脱氢催化剂的影响支持和粒度

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摘要

The efficacy of tandem dehydrogenation-condensation catalysts for the upgrade of bio-derived intermediates is largely determined by their relative (de-)hydrogenation and decarbonylation activity. Here, the effects of support and particle size of heterogeneous PdCu alloy catalysts on (de-) hydrogenation and decarbonlylation reactions were investigated using kinetic measurements, X-ray absorption spectroscopy and density functional theory (DFT). The chemical mismatch of Cu2+ with Ti4+ and Ca2+ prevents the substitution of Cu into the lattice of TiO2 or hydroxyapatite supports, and facilitates its alloying with Pd, resulting in improved selectivity for hydrogenation-dehydrogenation reactions compared to decarbonylation reactions. Based on kinetic measurements of butyraldehyde reactions over Pd and PdCu/SiO2 model catalysts, decarbonylation activity is attributed to the presence of Pd surface ensembles, while (de-)hydrogenation reactions are catalyzed by PdCu sites on the surface. This is consistent with selectivity and CO coverage trends with increasing conversion, and DFT-based microkinetic modeling. Selectivity control can also be achieved using the PdCu nanocluster size. Smaller nanoparticles favor the C-CO bond scission step of the decarbonylation reaction, due to the stronger binding of CO and alkyl species to sites of lower coordination. CO-induced segregation of reactive Pd atoms to under-coordinated step/edge sites also amplifies the geometric effect on the catalytic behavior.
机译:串联的功效dehydrogenation-condensation催化剂的bio-derived中间体主要的升级由它们的相对(de)加氢和脱羰作用活动。异构的支持和颗粒大小PdCu合金催化剂(de)加氢和decarbonlylation反应研究使用动态测量、x射线吸收光谱和密度泛函理论(DFT)。的化学不匹配Cu2 +四价和Ca2 +防止替代铜的晶格二氧化钛或羟磷灰石的支持促进其与Pd的合金化,导致改进的选择性hydrogenation-dehydrogenation反应相比脱羰作用反应。测量在Pd的丁醛反应PdCu /二氧化硅模型催化剂、脱羰作用活动是归因于Pd的存在表面集合体,而(de)加氢反应是催化PdCu网站表面。公司报道趋势随着转换,和DFT-based microkinetic建模。也可以通过使用PdCu的控制纳米大小。C-CO债券脱羰作用的分离步骤反应,由于CO和更强的约束力烷基物种网站更低的协调。CO-induced隔离活性Pd的原子在协调步骤/边缘网站也放大几何影响催化行为。

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