Selective hydrogenation reactions are essential in the purification of light olefins by removal of polyunsaturated hydrocarbon impurities (alkynes/alkadienes). Pd-based catalysts are typically used because of their high activity at ambient temperatures. Unfortunately, retaining high selectivity at high conversion using a Pd catalyst is challenging, resulting in more undesired alkane formation, which is often ascribed to intrinsic properties of the Pd metal. However, in this work we show that heat and mass transport effects strongly impact the catalytic activity and selectivity of Pd nanoparticles on carbon catalysts (Pd/C) in the selective hydrogenation of butadiene. By systematically varying the Pd loading and catalyst grain size, we show that higher loadings and larger grains strongly decrease the butene selectivity. This is ascribed to an effect of internal diffusion limitations, arising from butadiene depletion in the core of the catalyst grains, and not by intrinsic properties of Pd. The comprehensive assessment of heat and mass transport phenomena is essential to reliably relate experimental observations to catalyst properties such as Pd particle size, support or promoter effects. It contributes to the understanding and rational design of catalysts for selective hydrogenation of butadiene and can be extended to other reactions and/or supported metal catalysts.

中文翻译：

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负载 Pd 上 1,3-丁二烯气相选择性加氢过程中的传质效应

选择性加氢反应对于通过去除多不饱和烃杂质（炔烃/链二烯）来纯化轻质烯烃至关重要。通常使用钯基催化剂，因为它们在环境温度下具有高活性。不幸的是，使用钯催化剂在高转化率下保持高选择性具有挑战性，导致更多不期望的烷烃形成，这通常归因于钯金属的固有性质。然而，在这项工作中，我们表明，在丁二烯选择性加氢中，热和质量传递效应强烈影响碳催化剂（Pd/C）上钯纳米颗粒的催化活性和选择性。通过系统地改变 Pd 负载量和催化剂颗粒尺寸，我们发现较高的负载量和较大的颗粒会强烈降低丁烯的选择性。这是由于催化剂颗粒核心的丁二烯消耗引起的内部扩散限制的影响，而不是 Pd 的固有特性。热和质量传递现象的综合评估对于可靠地将实验观察结果与催化剂特性（例如钯粒径、载体或促进剂效应）联系起来至关重要。它有助于理解和合理设计丁二烯选择性加氢催化剂，并可扩展到其他反应和/或负载型金属催化剂。