Abstract
A series of titanate nanotube-supported metal catalysts (M/TNTs, M = Rh, Au orAu–Rh) were facilely synthesized. The effects of different Au contents, reduction processes and sequence of loading metals on their catalytic performances in the hydroformylation of vinyl acetate were comparatively investigated. The results showed that some Au and Rh formed bimetallic particles. Furthermore, the presence of Au in catalysts could significantly improve the selectivity of reaction for aldehydes. Compared with the monometallic catalysts (Rh0.33/TNTs-1 and Au0.49/TNTs-2), the resultant bimetallic catalysts exhibited significantly higher selectivity for aldehydes as well as higher TOF values in the hydroformylation of vinyl acetate. Among them, Au0.52/Rh0.32/TNTs-12 displayed the best catalytic performance. The corresponding selectivity for aldehydes was as high as 88.67%and the turnover frequency (TOF) reached up to 3500 h−1. In addition, for the reduction of Rh3+ and Au3+ ions, the photo-reduction and ethanol-reduction were the optimal techniques under the present conditions, respectively.
Highlights
Hydroformylation is a process of producing fatty aldehydes with one more carbon atom compared to the original olefins with carbon monoxide and hydrogen in the presence of catalysts under pressure [1,2,3,4]
In our previous work [41], we found that the Rh-Ru/titanate nanotubes (TNTs) bimetallic catalysts with two types of active sites showed satisfactory catalytic performance in cyclohexene hydroformylation but poor selectivity for aldehydes in hydroformylation of vinyl acetate
The metal contents are measured by Inductively coupled mass spectrometer (ICP) analysis
Summary
Hydroformylation is a process of producing fatty aldehydes with one more carbon atom compared to the original olefins with carbon monoxide and hydrogen in the presence of catalysts under pressure [1,2,3,4]. Since its discovery in 1938, the hydroformylation reaction has become an important one-step synthesis pathway for aldehydes from a wide range of cheap olefins. More than 12 million tons of aldehydes worldwide are produced by the hydroformylation reaction every year. The homogeneous catalysts that are widely used in hydroformylation in the industrial field are usually mononuclear complexes, which display remarkable catalytic performance [5,6,7,8]. It is difficult to separate these homogeneous catalysts from the reaction system. Many strategies have been developed, such as aiming to heterogenize the homogeneous catalysts by anchoring them to various solid supports [9,10,11,12,13]
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