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Abstract: Transition metal substituted polyoxometalate (TMSP) compounds were used as catalysts for the liquid-phase oxidation of benzene to phenol by molecular oxygen with ascorbic acid as a reducing agent in an acetone/sulfolane/water mixed solvent. [(C4H9)4N]5[PW11CuO39(H2O)] is the best catalyst tested in this study. It showed 9.2% benzene conversion (TON=25.8) and 91.8% selectivity to phenol for the oxidation of benzene at 323K for 12h. The effect of the substituted transition metal in the TMSP compounds on the benzene conversion is in the order: Cu>V>Fe≫Mn>Ti>Cr>Co>Ni>Zn. The effect of the central atom in the TMSP compounds on the benzene conversion is in the order: P≈Si>Ge>B. [SiW11O39]8− is a good polyoxometalate ligand for transition metal ions as [PW11O39]7− for the oxidation of benzene. The selectivity to phenol was dramatically improved by adding the sulfolane solvent, but the benzene conversion decreased when a large amount of sulfolane was used in the mixed solvent. Ascorbic acid is indispensable for forming phenol from benzene oxidation by O2 over TMSP compounds. Higher O2 pressure in the catalytic system ensured more oxygen molecules solving in the solvent, and promoted the benzene conversion. [Copyright &y& Elsevier]

Ti- and Al-containing MCM-41 (Al-c-MCM-41 and Al–Ti-c-MCM-41) have been synthesized and tested for direct oxidation of propylene with molecular oxygen. The reaction occurred over Al- and Ti-containing MCM-41 like materials. Al–Ti-c-MCM-41 was found to be more effective than Al-c-MCM-41, while no product was formed for MCM-41 alone. The catalyst performances of Al–Ti-c-MCM-41 at 523 K were dependent on the Si/Al2 and Si/Ti ratios and the highest PO yield was 3% when Si/Al2 of 150 and Si/Ti ratios of 100 were used. A postulated scheme containing Al and Ti species is proposed. [Copyright &y& Elsevier]

The Pd(OAc)2/Ti—Al-HMS/CH3OH catalyst system showed 61.2% selectivity for PO at 42.8% propylene conversion for the oxidation of propylene with molecular oxygen in an autoclave reactor at 373 K for 4 h. The catalyst is reusable using the filtration method or the vacuum distillation method after reaction. It is likely that a Ti cyclic peracid-like intermediate was formed in the system made up of a Ti site, an oxygen molecule and a methanol molecule. The Pd species activates the oxygen molecule and the Al site plays a role for stabilizing the Ti cyclic peracid-like intermediate to improve the yield of propylene oxide from the oxidation of propylene with molecular oxygen. [ABSTRACT FROM AUTHOR]

Ti and Al containing MCM-41 (Al-c-MCM-41 and Al-Ti-c-MCM-41) have been synthesized and tested for direct oxidation of propylene with molecular oxygen. Al-Ti-c-MCM-41 is more effective than Al-c-MCM-41, while no product was formed for MCM-41 alone. It is also found that MCM-22 with Si/Al2 ratio of 30 and Na/SiO2 ratio of 0.18 is active for the reaction and a highest PO yield of 11.3% was obtained at 573 K. [Copyright &y& Elsevier]

The transition metal salts (Cu2+, Co2+ and Ni2+) of 10-molybdo-2-vanadophosphoric acid (H5[PMo10V2O40]) were supported on hexagonal mesoporous silica (HMS), and the resultant materials were used as catalysts for the selective oxidation of propylene to acetone by molecular oxygen. CuH3[PMo10V2O40]/HMS showed a high selectivity for acetone of 84.2% at 17.8% propylene conversion in a tubular fixed-bed reactor system under atmospheric pressure at 423 K. The high yield of acetone over CuH3[PMo10V2O40]/HMS at 423 K resulted from the proper acidity and oxidation ability of the heteropoly compound, the nature (acid property, redox property, etc.) of the Cu2+ counter-ion, the high surface area of the HMS support and the proper reaction temperature for the propylene oxidation. [Copyright &y& Elsevier]