Barberis Laura, Hakimioun Amir H, Plessow Philipp N, Visser Nienke L, Stewart Joseph A, Vandegehuchte Bart D, Studt Felix, de Jongh Petra E
Materials Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands.
Institute of Catalysis Research and Technology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen 76344, Germany.
Nanoscale. 2022 Sep 29;14(37):13551-13560. doi: 10.1039/d2nr02612k.
Converting CO into value-added chemicals and fuels, such as methanol, is a promising approach to limit the environmental impact of human activities. Conventional methanol synthesis catalysts have shown limited efficiency and poor stability in a CO/H mixture. To design improved catalysts, crucial for the effective utilization of CO, an in-depth understanding of the active sites and reaction mechanism is desired. The catalytic performance of a series of carbon-supported Cu catalysts, with Cu particle sizes in the range of 5 to 20 nm, was evaluated under industrially relevant temperature and pressure, 260 °C and 40 bar(g). The CO hydrogenation reaction exhibited clear particle size effects up to 13 nm particles, with small nanoparticles having the lower activity, but higher methanol selectivity. MeOH and CO formation showed a different size-dependence. The TOF increased from 1.9 × 10 s to 9.4 × 10 s with Cu size increasing from 5 nm to 20 nm, while the TOF was size-independent (8.4 × 10 s on average). The apparent activation energies for MeOH and CO formation were size-independent with values of 63 ± 7 kJ mol and 118 ± 6 kJ mol, respectively. Hence the size dependence was ascribed to a decrease in the fraction of active sites suitable for CO formation with decreasing particle size. Theoretical models and DFT calculations showed that the origin of the particle size effect is most likely related to the differences in formate coverage for different Cu facets whose abundancy depends on particle size. Hence, the CO hydrogenation reaction is intrinsically sensitive to the Cu particle size.
将一氧化碳转化为增值化学品和燃料，如甲醇，是一种有望减少人类活动对环境影响的方法。传统的甲醇合成催化剂在一氧化碳/氢气混合物中效率有限且稳定性差。为了设计出对一氧化碳有效利用至关重要的改进型催化剂，需要深入了解活性位点和反应机理。在工业相关的温度和压力（260℃和40巴（表压））下，对一系列铜粒径在5至20纳米范围内的碳负载铜催化剂的催化性能进行了评估。一氧化碳加氢反应在粒径达到13纳米之前表现出明显的粒径效应，小纳米颗粒活性较低，但甲醇选择性较高。甲醇和一氧化碳的生成表现出不同的粒径依赖性。随着铜粒径从5纳米增加到20纳米，甲醇生成的转化频率从1.9×10⁻³ s⁻¹增加到9.4×10⁻³ s⁻¹，而一氧化碳生成的转化频率与粒径无关（平均为8.4×10⁻³ s⁻¹）。甲醇和一氧化碳生成的表观活化能与粒径无关，分别为63±7千焦/摩尔和118±6千焦/摩尔。因此，粒径依赖性归因于随着粒径减小，适合一氧化碳生成的活性位点比例降低。理论模型和密度泛函理论计算表明，粒径效应的起源很可能与不同铜晶面的甲酸盐覆盖度差异有关，而这些晶面的丰度取决于粒径。因此，一氧化碳加氢反应本质上对铜粒径敏感。
