Vanadium doped titania

Wu, J.C.S and Chen, C.H. (2004) A visible-light response vanadium-doped titania nanocatalyst by sol-gel method. 

Xu, J., Y. Ao, M. Chen, D. Fu, and C. Yuan, Photocatalytic activity of vanadium-doped titania-activated carbon composite film under visible light. 

Preparation, physicochemical characterization and catalytic properties of vanadium-doped alumina- and titania-pillared montmorillonites... 

Procedures leading to preparation of vanadium-doped alumina- and/or titania-pillared montmorillonites are described and physicochemical characterization (chemical analysis, XRD, BET, ESR) of the products is provided. Results show that introduction of vanadium into the pillared montmorillonites leads to a rigid association of the dopant with pillars, irrespective of the method of preparation. The mode of vanadyl attachment in alumina-pillared samples does not depend on the mode of preparation, while in titania-pillared montmorillonite it does. Certain degree of delocalization of the unpaired electron into ligands and increased in-plane 7t-covalent bonding is observed for vanadyl ions present in the co-pillared (V-Ti)-PILC samples which also show particularly high activity in catalytic ammoxidation of m-xylene to nitrile product, as monitored by IR. A hypothesis is advanced that this effect is due to the unique character of vanadyl species present in these catalysts. 

This paper describes preparation, physicochemical characterization and catalytic properties of a series of vanadium-doped alumina- and titania-pillared montmorillonites obtained by various methods The aim of this work was to investigate the influence of the preparation procedure and pretreatment on location of vanadium dopant within the PILC structure and to correlate the physicochemical characteristics of tiie samples with their catalytic activity in ammoxidation of m-xylene. 

ESR data presented in detail elsewhere [7] show that all vanadium-doped alumina-and/or titania-pillared montmorillonite samples contain immobilized vanadyl ions bound to the pillars. 

Figure 1. ESR spectra at 77 K of vanadium-doped (a) alumina- and (b) titania-pillared samples. Vertical lines are drawn to facilitate comparison of parallel features of the spectra.

Vanadium oxide and cerium oxide have also been used to dope titania-zirconia mixed oxides. Their results will be discussed in the next section. 

Performance improvement in 1102 is achieved by doping the titania with platinum or vanadium oxide and copper. In order to improve the adsorption characteristics of Ti02, attempts have been made to support fine Ti02 on the porous adsorbent materials such as silica, alumina, activated carbon, clay, and zeolites. Ti02-supported adsorbent provides higher specific surface area and introduces more effective adsorption sites than bare Ti02. Decomposition rates of the substrates are found to increase due to one or... 

In the case of titania-pillared samples containing vanadium deposited onto calcined pillars (V-(Ti-PILC)-IA, V-(Ti-PILC)-IB, V-(Ti-PILC)-IC) the activity of nitrile formation increases with V content (Fig. 3) Comparison with the behaviour of the V-(Ti)-PILC sample containing vanadium introduced on uncalcined pillars shows that CN bands of similar intensity are formed for similar levels of doping, in agreement with the ESR data showing the same type of spectra... 

Titania-zirconia mixed oxides doped with vanadium and cerium oxides were also explored. The Ti02-Zr02 mixed oxide support, synthesized by a co-precipitation... 

In general, the ammoxidation reactions are carried out in the presence of a heterogeneous catalysts at elevated temperatures, slightly increased pressure and in the gas phase. Multicomponent oxidic catalysts, mainly containing transition metal oxides are in use. Most catalysts for olefin conversions consist of bismuth and molybdenum oxides. They can be doped by a wide variety of further transition metals. In addition, oxide components like silica, alumina and titania are incorporated as inert diluents or active constituents. The catalysts for the reactions of aromatics and hetero-aromatics mainly contain vanadium, molybdenum and other transition metals. In addition, the reaction can also be carried out in liquid phase. The reported literature on this subject is rather scanty. 

From the results above, it can be concluded that the surface properties of sodium-doped, vanadia-containing alumina and titania depend on the parameters here studied, i.e., the precursor salt of vanadium (although its effect is cancelled upon calcination at 973K), the calcination temperature and the presence of sodium. Formation of ternary V-Al-O compounds in the Na-rich samples leads to removal of pores with an average diameter of 8 nm, probably because of the soldering of the alumina primary particles. 

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