Structure–activity relationships over Ru/NiAl2O4 catalysts in anisole demethoxylation: spectroscopic and kinetic studies
Lingxiao Li, Zhiruo Guo, Xiaohui Liu, Mohsen Shakouri, Yongfeng Hu, Yong Guo, Yanqin Wang
Abstract
Abstract Demethoxylation was kinetically and spectroscopically studied over three catalysts with different Ru 0 /Ru δ+ ratios. In-situ spectroscopic tests demonstrated that the synergy between Ru 0 and Ru δ+ was crucial, and Ru 0 was in charge of H 2 activation and adsorption of aromatic ring while Ru δ+ adsorbed with O in methoxyl. A Langmuir–Hinshelwood kinetic model was proposed, and ratio of Ru 0 /Ru δ+ was the key in deciding the rate-determining step (RDS): i) desorption of toluene was RDS over catalyst with high Ru 0 ratio; ii) dissociation of H 2 was RDS over Ru δ+ enriched catalyst; iii) demethoxylation was rate-determined by CO water–gas shift (WGS) when Ru 0 /Ru δ+ approached ~ 1. The best performance was obtained over Ru/NiAl 2 O 4 -200, which effectively enabled both C-O bond activation and rapid recovery of adsorption sites for aromatic rings. Finally, in-situ DRIFT studies on methoxy decomposition and CO-WGS unraveled that the electronic composition of Ru was more stable in Ru/NiAl 2 O 4 -200 which contributes to its excellence.