Catalytic performance of niobium species in crystalline and amorphous solids—Gas and liquid phase oxidation

This paper is devoted to the role of niobium, located in crystalline and amorphous catalysts, in catalytic oxidation reactions. Bulk niobium(V) oxides (crystalline and amorphous), NbMCM-41, NbSBA-3, NbSBA-15 and NbY materials were used as catalysts in gas phase oxidation of methanol with oxygen, liquid phase oxidation of glycerol with oxygen and liquid phase oxidation of cyclohexene with hydrogen peroxide. When H2O2 was applied as an oxidation agent the amorphous materials containing niobium species were the most effective catalysts because Nb in such catalysts strongly interacts with H2O2 resulting in the formation of active ONb(V)O2 radicals. It was not the case for crystalline catalysts containing niobium. The results obtained for Nb-containing materials used as supports for copper, gold and binary Sb–V–Ox oxides indicated that niobium species promotes stabilization of the active species loaded. Moreover, it was shown that gold loaded on crystalline niobia increases the catalytic activity in dehydrogenation of methanol and glycerol, which is the first step of their oxidation with oxygen.

Nb-containing molecular sieves and Nb2O5 (crystalline and amorphous) were used as catalysts in gas phase oxidation of methanol with oxygen, liquid phase oxidation of glycerol with oxygen and cyclohexene with hydrogen peroxide. H2O2 interacts with the amorphous catalysts towards ONb(V)O2 radicals very active in epoxidation of cyclohexene. It is not the case for Nb in crystalline catalysts, which are active in chemisorption of alcohols.Figure optionsDownload high-quality image (64 K)Download as PowerPoint slideResearch highlights▶ Difference in oxidation activity if Nb located in amorphous or crystalline catalyst. ▶ H2O2 as oxidant – formation of active ONb(V)O2 radicals if amorphous catalyst. ▶ Nb in amorphous oxide – active but not selective in MeOH oxidation. ▶ Nb dispersed in amorphous mesoporous silica active and selective in oxidation. ▶ Nb in supports promotes stabilization of active species loaded (Cu, Au, Sb–V–Ox).