Crystalline CrV_1-xP_xO_4 catalysts for the vapor-phase oxidation of 3-picoline

摘要

The heterogeneously catalyzed vapor-phase oxidation of 3-picoline to nicotinic acid over a series of mixed oxides C_rV1-xP_xO_4 was investigated at 300-400 deg C Characterizations of th catalysts were carried out using X-ray diffraction FT-IR TG-DTA BET,NH_3-TPD TPR and pyridine adsorption diffuse reflectance infrared Fourier-transform spectra (DRIFTS)The mized oxides C_rV_1-x P_xO_4 (x=0-1.0) were precipitated by addjusting the pH from an aqueous solution of th mixture of the raw materials The precipitates were calcined at 550-700 deg C and employed as the catalyst for the selective oxidatin of 3-picoline During the calcinatin a crystallization of monoclinic CrVO_4-I phase of alpha-MnMoO_4 structure was clearly observed by TG-DTA FT-IR and XRD analyses of the CrV_1-xP_XO_4 in the range of x<0.1 In these CrV_1-xP_xO_4 p atoms replace V atoms in the VO_4 tetrahedra still keeping a monoclinic CrVO_4-I structured This structure changed to amorphous by further addition of P(x>0.25) or to orthorhombic CrVO_4-III by further calcination at thigh temperature (>700 deg C) resulting in the catalyst deactivatin It was found that CrVO_4-I was originally active and the additio of a small amount of Presulted in a high enhancement in te catalytic activity CrV_0.95P-0.05O_4 showed the highest activity among the catalysts tested NH_3-TPD showed an increase in the acid site by replacing V with a small amount of P in CrVO_4-I was originally active and the addition of a small amount of P resulted in a highe enhancedment in the catalytic activity C_rV_0.95P_0.05O_4 A favorable effect of water additio suggests that Gronsted adid assists the selective oxidatin and this was confirmed by infrared study of pyridine adsorption on the cztlaysts The active catalysts C_rV_1-xP_xO_4(O