Partial oxidation of toluene to benzaldehyde and benzoic acid over model vanadia/titania catalysts: role of vanadia species

Abstract

Pure and K-doped vanadia/titania prepared by different methods have been studied in order to elucidate the role of vanadia species (monomeric, polymeric, bulk) in catalytic toluene partial oxidation. The ratio of different vanadia species was controlled by treating the catalysts in diluted HNO 3 , which removes bulk vanadia and polymeric vanadia species, but not the monomeric ones, as was shown by FTRaman spectroscopy and TPR in H 2 . Monolayer vanadia species (monomeric and polymeric) are responsible for the catalytic activity and selectivity to benzaldehyde and benzoic acid independently on the catalyst preparation method. Bulk V 2 O 5 and TiO 2 are considerably less active. Therefore, an increase of the vanadium concentration in the samples above the monolayer coverage results in a decrease of the specific rate in toluene oxidation due to the partial blockage of active monolayer species by bulk crystalline V 2 O 5 . Potassium diminishes the catalyst acidity resulting in a decrease of the total rate of toluene oxidation and suppression of deactivation. Deactivation due to coking is probably related to the Brønsted acid sites associated with the bridging oxygen in the polymeric species and bulk V 2 O 5 . Doping by K diminishes the amount of active monolayer vanadia leading to the formation of non-active K-doped monomeric vanadia species and KVO 3 . # 2004 Elsevier B.V. All rights reserved.

Engineering Cobalt Oxide with Coexisting Cobalt Defects and Oxygen Vacancies for Enhanced Catalytic Oxidation of Toluene

“…The adsorption band at 2342 cm −1 is attributed to CO 2 , and the broad band at 3375 cm −1 is assigned to H 2 O. 58,60 Besides, the vibrational band between 3565 and 3670 cm −1 is attributed to the coordinated hydroxyl groups, 61 while the band at 3070 cm −1 is characteristic of υ(CH−) stretching vibration of the methyl (−CH 3 ) group on the toluene aromatic ring. 62−64 Additionally, the adsorption band around 1602−1798 cm −1 is attributed to benzoquinone, 65 and the one at 1757 cm −1 is assigned to phenol.…”

Interaction between Monomeric Vanadium Oxide Clusters Supported on Titania and Its Influence on Their Reactivity

“…Submonolayers of vanadium oxide supported on another oxide are good catalysts for several partial oxidation reactions and their properties have been examined in several recent review articles. − There is strong evidence that catalytic chemistry of vanadium oxide supported on an oxide is most useful when the VO x coverage is less than or equal to a monolayer. − The chemistry of such supported VO x clusters has been examined in a large number of computational studies. − In this paper we are concerned with monomeric VO x supported on rutile TiO 2 (110). We have chosen to study a TiO 2 support because VO x /TiO 2 is an industrially important catalyst, its structure can be imaged by STM, − and experiments with mass selected clusters have been performed. , The quality and the quantity of the information we have for this system is better than for any other support.…”

Supported vanadium oxide in heterogeneous catalysis: elucidating the structure–activity relationship with spectroscopy

“…In modern heterogeneous catalysis, supported vanadium oxide catalysts constitute a very important class of catalytic materials. They have become the model for catalytic systems for fundamental studies of supported metal oxides and they are widely used as selective oxidation catalysts in the industrial production of economically attractive redox reactions, like the oxidation of methane, [1][2][3][4][5][6][7] propane, 8,9 butane, [10][11][12] toluene, [13][14][15][16][17] benzene, 18,19 propene, 20 o-xylene, 21 methanol, [22][23][24][25][26][27][28] ethanol, 29,30 formaldehyde, 31 several oxidative dehydrogenations, [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]…”