Preparation And Catalytic Activity Of Heteropoly Compound Catalysts

A series of heteropoly compound (HPC) catalysts, including 12-phosphotungstic acid (PW) and its cesium salt and potassium salt, immobilized on various supports such as amorphous silica (SiO₂), mesoporous molecule sieve (SBA-15), ultra stable Y zeolite (USY) and dealuminated ultra stable Y zeolite (DUSY), were prepared by impregnation. Their physicochemical properties were characterized by X-ray diffraction (XRD), N2 adsorption, temperature programmed desorption of ammonia (NH3-TPD), Hammett indicator, infrared-ray spectrum (IR), 31P MAS NMR and scanning electrical microscope (SEM). The catalytic behavior was investigated in acidic catalyzed reactions, such as esterification of n-butanol with acetic acid to synthesize n-butyl acetate and acetalization of ethyl acetoacetate with ethylene glycol or 1,2-propanediol to synthesize fructone or fructone-B. The catalytic stability was also evaluated by water treatment test. In addition, Keggin-type heteropoly acids H3+nPMo12-nVnO40?xH2O (abbreviated as PMoVn, n=1-3) were developed by an environmentally benign method. The catalysts were characterized by ICP, XRD, thermal gravimetric analysis (TG), UV-Vis, IR and MAS NMR, and their catalytic activities were investigated in hydroxylation of benzene to phenol carried out in a mixed solvent of acetonitrile and acetic acid with aqueous hydrogen peroxide as oxidant.It is found that the catalytic activity relates closely with the catalyst surface area, acid amount and the dispersion of PW on the surface of the support SiO₂. For the catalyst with a PW loading of 40 %, the optimal reaction conditions are as follows: reaction temperature is 395 K, reaction time is 120 min, and the catalyst mass fraction is 3.5 % in the reaction medium. In this case, n-butanol conversion of 89.8% with the selectivity of n-butyl acetate being 100% would be achieved. In the synthesis of fructone, the catalytic activity increased with the increase of PW loading; the conversion of ethyl acetoacetate reached stable value when the loading reached 30% with the conversion for PW/SiO₂ being 69.8%, Cs2.5PW/SiO₂ being 68.6% and K2.5PW/SiO₂ being 68.4%, respectively. The water treatment test also showed that deactivity of catalyst was correlated with leaching of HPC, and the sequence of catalytic stability was 30%Cs2.5PW/SiO₂≈30%K2.5PW/SiO₂>30%PW/SiO₂.