Characterization of Vanadium Oxide–Zirconia Catalyst

Spectroscopic Studies on ZrO2Modified with MoO3and Activity for Acid Catalysis

“…24,25 The catalyst in a glass tube was pretreated at 400 o C for 1 hr and filled with dry nitorgen. For the determination of acid strength of the catalyst the color changes of indicators were observed by spot test.…”

“…For the 5-MoO 3 /ZrO 2 , as shown in Figure 5, X-ray diffraction data indicated tetragonal ZrO 2 form at 400-600 o C, and a two-phase mixture of the tetragonal and monoclinic ZrO 2 forms at 700-900 o C. It is assumed that the interaction between molybdenum oxide and ZrO 2 hinders the transition of ZrO 2 from amorphous to tetragonal phase. 21,24 The presence of molybdenum oxide strongly influences the development of textural properties with temperature. No phase of molybdenum oxide was observed at any calcination temperature, indicating a good dispersion of molybdenum oxide on the surface of ZrO 2 support due to the interaction between them.…”

“…ZrO 2 is a two-phase mixture of the tetragonal and monoclinic forms up to 3 wt%, but for sample containing MoO 3 equal to or above 15 wt%, ZrO 2 was amorphous because the interaction between MoO 3 and ZrO 2 hinders the phase transition of ZrO 2 from amorphous to tetragonal phase. 21,24 It is also of interest to examine the influence of molybdenum oxide on the transition temperature of ZrO 2 from tetragonal to monoclinic phase. In view of X-ray diffraction patterns, the calcination temperatures at which monoclinic phase is observed initially are 500 o C for pure ZrO 2 , 700 o C for 5-MoO 3 /ZrO 2 , 800 o C for 15-MoO 3 /ZrO 2 , respectively.…”

Effect of Al2O3Addition and WO3Modification on Catalytic Activity of NiO/Al2O3-TiO2/WO3for Ethylene Dimerization

“…It is assumed that the interaction between Al 2 O 3 and TiO 2 hinders the phase transition of TiO 2 from amorphous to anatase. 32,44,45 The XRD patterns of 20NiO/5Al 2 O 3 -TiO 2 /WO 3 calcined at 400 °C for 1.5 h as a function of WO 3 content are shown in Figure 4. WO 3 remained amorphous to X-ray diffraction up to 15 wt%, indicating good dispersion on the surface of catalyst.…”

“…The amount of two phases of TiO 2 and WO 3 increased with increasing calcination temperature, indicating that the interaction between NiO or WO 3 and TiO 2 hinders the transition of TiO 2 from amorphous to anatase phase. 44,47 The presence of NiO and WO 3 strongly influences the development of textural properties with temperature in comparison with pure TiO 2 . In fact, it is reported that for pure TiO 2 two phases of anatase and rutile TiO 2 are present at the calcination temperature of 350 °C because of no interaction of titania.…”