Analysis of thermally induced solid-solid interactions in vanadia-alumina system

Abstract

V2Os/AI203 solids of varying compositions were prepared, dried at 100*C and calcined in air at 400-10000C. The solid-solid interactions between the mixed oxides were investigated by means of DTA, TG and XRD techniques.The results revealed that ammonium metavanadate and aluminium hydroxide decomposed at 260 and 290~ respectively, to yield an ammonium vanadium intermediate compound and AI~O3 as solids. The intermediate compound readily decomposed at 360~ to give V205.Solid V:Os generally catalyses the crystallization of A1203 to an extent proportional to its amount present. The solid-solid interactions between A1203 and V:O3 to produce A1V204 and AIVO4 took place at 750 and 900~ These solids decomposed entirely at 1000oC, producing V205 and alpha-corundum. The pure A1203 samples employed existed as amorphous solids even when heated in air at 750~ but in the presence of V205 (7-18 wt. %) they crystallized to thetaalumina at 600~ The pure solid alumina crystallized at 1000~ to a mixture of theta and kappaalumina. In the presence of V205, alpha-corundum together with kappa and theta phases was obtained on heating at 900~

Surface and Catalytic Properties of the CuO/Al2O3 System as Influenced by Doping with CeO2 or ZrO2 and by γ-Irradiation

“…Similar results have been obtained for ZnO doping of the CuO/Al 2 O 3 system (El-Shobaky et al 2001a) and the Co 3 O 4 /Al 2 O 3 system (Chin and Hercules 1982;El-Shobaky et al 2001b). Such findings indicate that ZrO 2 doping led to an increase in the degree of dispersion of the CuO phase in the CuO/Al 2 O 3 system.…”

“…Similar results for H 2 O 2 decomposition have been reported for g-irradiated CuO-ZnO/Al 2 O 3 solids and were attributed to the progressive removal of -OH groups from the solid surface as a result of g-irradiation (Fagal et al 1998). However, exactly opposite results for the same catalytic system in the oxidation of CO by O 2 have been reported by El-Shobaky et al (1997b). These latter authors explained the increase in the reaction rate induced by g-irradiated CuO-ZnO/Al 2 O 3 solids used as catalysts in the latter reaction as due to the progressive removal of surface -OH groups blocking the catalyst surface and preventing its complete participation in the chemisorption and catalysis of the CO oxidation reaction.…”

“…The catalytic activity and stability of CuO can be greatly improved by loading it on to finely divided support materials, doping the solid with certain foreign oxides and treating the same with ionizing radiation. CeO 2 and g-Al 2 O 3 have been used as convenient supports for precious metals and copper oxide catalysts (Yao and Yao 1984;Lin and Stephanopoulos 1995a,b;Luo et al 1997;El-Shobaky et al 1988, 1990. Use of a support material increases the degree of dispersion of catalytically active constituents and hinders their grain growth, thereby increasing their catalytic activities and stabilities.…”

“…Oxides such as Li 2 O, Na 2 O, K 2 O, ZnO, MoO 3 , Cr 2 O 3 and ZrO 2 have frequently been employed as dopants for supported iron, cobalt, nickel and copper oxide catalysts (El-Shobaky and Al-Noaimi 1987a,b;El-Shobaky et al 1987, 1994a,b, 1995, 1997a,b, 1998aGhozza et al 2000;Gines et al 1997;Severino et al 1986;Luo et al 1997;Xian-Zhou et al 1997;Bolt et al 1994).…”

Thermal solid–solid interactions and catalytic properties of V2O5/Al2O3 system treated with Li2O and Ag2O

“…This means that V 2 O 5 dissolved in the matrix of alumina and enhanced the crystallization process of ␥-Al 2 O 3 into ␣-Al 2 O 3 . This behaviour has been observed in the case of Al 2 O 3 treated with MoO 3[2,15].3.4. XRD investigation of pure solid doped with Li 2 O andAg 2 O fired at 350-1000 • C The XRD patterns of the pure solids treated with different amounts of Li 2 O or Ag 2 O in mol%; only 0.40 and 4.58 ratios were represented here; and calcined in air at 350, 550, 750 and 1000 • C were illustrated in Figs.…”