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Surface acidic and redox properties of V-Ag-Ni-O catalysts for the selective oxidation of toluene to benzaldehyde

Paper ID Volume ID Publish Year Pages File Format Full-Text
43454 45970 2007 10 PDF Available
Title
Surface acidic and redox properties of V-Ag-Ni-O catalysts for the selective oxidation of toluene to benzaldehyde
Abstract

V-Ag-O and V-Ag-Ni-O complex oxides were found to exhibit good catalytic reactivity for the selective oxidation of toluene to benzaldehyde. In order to understand the effects of each metal in the two catalysts, a series of single and complex oxides were prepared including V2O5, Ag2O, NiO, V-Ni-O, Ag-Ni-O, V-Ag-O and V-Ag-Ni-O with the previously optimized compositions for the binary and tertiary oxides. Data from the X-ray diffraction (XRD), infrared spectroscopy and laser Raman spectroscopy showed the formation of complex oxides with phases of silver and nickel vanadates as well as the broadening and red shift of the band of VO bonds, suggesting the formation of VOAg and VONi bonds and the increased redox ability of vanadium species. The results from temperature programmed reduction (TPR) and the combined technique of TPR-XRD revealed that the addition of Ag and Ni promoted the reduction of vanadium species in the complex catalysts. Microcalorimetric adsorption of ammonia and the probe reaction of isopropanol in air demonstrated that the surface acidity was greatly decreased while the redox cycles of vanadium sites were significantly enhanced upon the addition of Ag and Ni. The reactivity for the selective oxidation of toluene was evaluated by using a fixed-bed microreactor, and was correlated with the surface acidity and redox property of the catalysts. Silver seemed to be a special promoter that not only decreased the surface acidity but also enhanced the redox cycles of vanadium sites, leading to the increased conversion of toluene and the selectivity to benzaldehyde. Such effect was even more pronounced when Ag and Ni were added simultaneously. Accordingly, the V-Ag-Ni-O catalyst studied in this work exhibited excellent performance for the selective oxidation of toluene to benzaldehyde. The conversion of toluene was found to be 8% with 95% selectivity to benzaldehyde on the V-Ag-Ni-O at 613 K.

Graphical abstractThe functions of Ag, Ni and V in the V-Ag-Ni-O complex catalyst for the selective oxidation of toluene to benzaldehyde were studied. The addition of Ag greatly decreased the surface acidity while increased the redox cycles of vanadium sites. Simultaneous addition of Ag and Ni further enhanced such effects, leading to the significantly increased conversion of toluene and selectivity to benzaldehyde.Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Vanadium oxide catalysts; Selective oxidation of toluene to benzaldehyde; Promote effect of Ag and Ni; Surface acidity; Redox cycles
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Surface acidic and redox properties of V-Ag-Ni-O catalysts for the selective oxidation of toluene to benzaldehyde
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 330, 10 October 2007, Pages 117–126
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us