Microporous Molybdenum - Tungsten - Phosphorus Series Catalysts And Their Catalytic Study

Heteropolyoxometalates are included in microporous silica, CsxH3-xPMo12O40/SiO2, CsyH5-yPMo10V2O40/SiO2 and CsxH5-xPW10V2O40-/SiO2 have been synthesized by a sol-gel technique and characterized by IR, UV-V1S, X-ray and N2 adsorption isotherms. IR and UV-VIS data indicate that the identities of CsxH3-xPMo12O40, CsyH5-yPMo10V2O40 and CsxH5-xPW10V2O40 are preserved within these synthesized compounds. TEM image and BET adsorption isotherms confirm the presence of nanometer particles and microporous structures. X-ray powder patterns prove that the cesium salts of the heteropolyoxometalates are uniformly dispersed in the silica network. As insoluble solid bifunctional catalysts, they show high catalytic activity and selectivity for selective oxidation of benzyl alcohol into benzyl aldehyde by H2O2 in liquid-solid systems. The highest activity is observed at x = 1.5 or y = 2.5 in CsxH3-xPMo12O40/SiO2, CsyH5-yPMo10V2O40/SiO2 and CsxH5-xPW10V2O40/SiO2, respectively.A novel class of inorganic materials, [AlO4Al12(OH)24(H2O)12]-[SiW11O39ZCl].11H2O (abbreviated Al13.SiW11Z, Z = Ni or Co), consisting ofKeggin cations and Keggin anions, has been synthesized and characterized by IR, NMR, X-ray and TGA. The infrared spectral and the MAS NMR spectroscopic data for the Al13-SiW11Z indicate that the identities of the clusters are preserved in the monolithic crystal Al13-SiW]]Ni and gel Al13-SiW11Co, and the Al13-SiW11Z is indeed a more symmetric structure. The X-ray powder pattern of the gel Al13-SiW11Co demonstrates its swelling properties.The hydrodenitrogenation (HDN) of o-methylaniline (OMA) and o-propylaniline (OPA) has been studied in a continuous microflow reactor over MoP, NiMoP and CoMoP catalysts supported on SiO2. Diffusion effects in the HDN of OMA and OPA were studied and it was found that the intermediates could not diffuse out of the pores fast enough to be detected. To avoid diffusion limitation, the particle sizes of the catalysts were reduced. The major part of theC-N cleavage of OMA and OPA take place via ring hydrogenation and p-Hofmann elimination. The HDN of 2-methylcyclohexylamine (MCHA) was studied because it is an intermediate in the HDN of OMA, which can be detected in addition to the main products methycyclohexene (MCHE) and methylcyclohexane (MCH) when a high quantity of cyclohexene was added to OMA during its HDN. MCHA is not observed in the HDN of OMA alone, because of its strong adsorption constant and high rate constant for reacting further to MCHE and MCH. Adding cyclohexene decreases the adsorption of MCHA, thus enabling its detection. The selectivity of MCH in the HDN of MCHA was about 20% at low conversion. The detection of 2-methylcyclohexane in the HDN of MCHA explains the C(sp3)-N bond cleavage showing that MCH is formed via nucleophilic substitution of the amine group of MCHA. Moreover, it was proved that the mechanism of the pathway from OMA to MB is different in the pathway from MCHA to MCH [direct C(sp3)-N]. All phosphides can increase reaction activity in the absence of H2S for the HDN of OMA and OPA. Prepared with traditional MoS2 system catalysts, MoP/SiO2 catalyst had the highest activity and simplified the technology process at the high degree.