Zhang Hong, Wang Xuelong, Liu Ping
Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, USA.
Chemistry Division, Brookhaven National Lab, Upton, NY 11973, USA.
Phys Chem Chem Phys. 2022 Jul 21;24(28):16997-17003. doi: 10.1039/d2cp01971j.
Conversion of CO to useful fuels and chemicals has gained great attention in the past decades; yet the challenge persists due to the inert nature of CO and the wide range of products formed. Pd-based catalysts are extensively studied to facilitate CO hydrogenation to methanol a reverse water gas shift (rWGS) pathway or formate pathway where formic acid may serve as an intermediate species. Here, we report the selective production of formic acid on the stable Pd(111) surface phase under CO hydrogenation conditions, which is fully covered by chemisorbed hydrogen, using combined Density Functional Theory (DFT) and Kinetic Monte Carlo (KMC) simulations. The results show that with the full coverage of hydrogen, instead of producing methanol as reported for Pd(111), the CO activation is highly selective to formic acid a multi-step process involving the carboxyl intermediate. The high formic acid selectivity is associated with surface hydrogen species on Pd(111), which not only acts as a hydrogen reservoir to facilitate the hydrogenation steps, but also enables the formation of confined vacancy sites to facilitate the production and removal of formic acid. Our study highlights the importance of reactive environments, which can transform the surface structures and thus tune the activity/selectivity of catalysts.
在过去几十年里，将一氧化碳转化为有用的燃料和化学品备受关注；然而，由于一氧化碳的惰性以及所形成的产物种类繁多，这一挑战依然存在。人们广泛研究了钯基催化剂，以促进一氧化碳加氢生成甲醇、通过逆水煤气变换（rWGS）途径或甲酸途径（其中甲酸可能作为中间物种）。在此，我们使用密度泛函理论（DFT）和动力学蒙特卡罗（KMC）模拟相结合的方法，报告了在一氧化碳加氢条件下，在稳定的Pd(111)表面相上选择性生产甲酸的情况，该表面相被化学吸附的氢完全覆盖。结果表明，在氢完全覆盖的情况下，与报道的Pd(111)生成甲醇不同，一氧化碳活化对甲酸具有高度选择性，这是一个涉及羧基中间体的多步过程。高甲酸选择性与Pd(111)表面的氢物种有关，它不仅作为氢库促进加氢步骤，还能形成受限空位以促进甲酸的生成和去除。我们的研究强调了反应环境的重要性，它可以改变表面结构，从而调节催化剂的活性/选择性。
