Qi Liang, Das Sonali, Zhang Yanfei, Nozik Danna, Gates Bruce C, Bell Alexis T
Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States.
J Am Chem Soc. 2023 Feb 8;145(5):2911-2929. doi: 10.1021/jacs.2c11075. Epub 2023 Jan 30.
Catalysts for hydroformylation of ethene were prepared by grafting Rh into nests of ≡SiOZn-OH or ≡SiOCo-OH species prepared in dealuminated BEA zeolite. X-ray absorption spectra and infrared spectra of adsorbed CO were used to characterize the dispersion of Rh. The Rh dispersion was found to increase markedly with increasing M/Rh (M = Zn or Co) ratio; further increases in Rh dispersion occurred upon use for ethene hydroformylation catalysis. The turnover frequency for ethene hydroformylation measured for a fixed set of reaction conditions increased with the fraction of atomically dispersed Rh. The ethene hydroformylation activity is 15.5-fold higher for M = Co than for M = Zn, whereas the propanal selectivity is slightly greater for the latter catalyst. The activity of the Co-containing catalyst exceeds that of all previously reported Rh-containing bimetallic catalysts. The rates of ethene hydroformylation and ethene hydrogenation exhibit positive reaction orders in ethene and hydrogen but negative orders in carbon monoxide. IR spectroscopy and the kinetics of the catalytic reactions suggest that ethene hydroformylation is mainly catalyzed by atomically dispersed Rh that is influenced by Rh-M interactions, whereas ethene hydrogenation is mainly catalyzed by Rh nanoclusters. IR spectroscopy also indicates that the ethene hydroformylation is rate limited by formation of propionyl groups and by their hydrogenation, a conclusion supported by the measured H/D kinetic isotope effect. This study presents a novel method for creating highly active Rh-containing bimetallic sites for ethene hydroformylation and provides new insights into the mechanism and kinetics of this process.
通过将铑接枝到脱铝BEA沸石中制备的≡SiOZn-OH或≡SiOCo-OH物种的巢状结构中，制备了用于乙烯氢甲酰化的催化剂。利用吸附CO的X射线吸收光谱和红外光谱对铑的分散情况进行了表征。发现铑的分散度随M/Rh（M = Zn或Co）比值的增加而显著提高；用于乙烯氢甲酰化催化时，铑的分散度进一步增加。在固定的一组反应条件下测得的乙烯氢甲酰化的周转频率随原子分散铑的比例增加而增加。对于M = Co，乙烯氢甲酰化活性比M = Zn时高15.5倍，而对于后一种催化剂，丙醛选择性略高。含钴催化剂的活性超过了所有先前报道的含铑双金属催化剂。乙烯氢甲酰化和乙烯加氢的速率对乙烯和氢气呈现正反应级数，而对一氧化碳呈现负反应级数。红外光谱和催化反应动力学表明，乙烯氢甲酰化主要由受Rh-M相互作用影响的原子分散铑催化，而乙烯加氢主要由铑纳米团簇催化。红外光谱还表明，乙烯氢甲酰化的速率受丙酰基的形成及其加氢的限制，这一结论得到了测量的H/D动力学同位素效应的支持。本研究提出了一种创建用于乙烯氢甲酰化的高活性含铑双金属位点的新方法，并为该过程的机理和动力学提供了新的见解。
