Enhanced Photocatalytic Performance of Anatase TiO_(2) by Deposition-Precipitation Treatment

Deposition-precipitation(DP)method is commonly used to prepare the supported metal catalysts.In this study,the modification effect of the mild DP method on the photocatalytic performance of TiO_(2)was investigated.The TiO_(2)samples with DP treatment,as well as Au/TiO_(2)prepared under the same conditions,showed enhanced photocatalytic performance of the degradation of methylene blue(MB).·OH generated by photoexcited holes is identified as the main intermediate reactive species during the degradation reaction.X-ray photoelectron spectroscopy(XPS)and Fourier transform infrared spectroscopy(FTIR)show that TiO_(2)(A)-17 after DP treatment has the most amount of surface OH^(-)_(ad)species.The presence of surface OH^(-)_(ad)species not only changes the surface zeta potential,favoring the attraction of cationic MB;but also depresses the electron-hole recombination,favoring photodegradation of MB by hole-produced·OH.An implication of these findings is that the modification of support properties should be taken into account while preparing supported metal catalysts using DP methods.

Enhanced catalytic activities and selectivities in preferential oxidation of CO over ceria-promoted Au/Al_2O_3 catalysts

The preferential oxidation of CO （CO‐PROX） is a hot topic because of its importance in pro‐ton‐exchange membrane fuel cells （PEMFCs）. Au catalysts are highly active in CO oxidation. Howev‐er, their activities still need to be improved at the PEMFC operating temperatures of 80–120 ＆#176;C. In the present study, Au nanoparticles of average size 2.6 nm supported on ceria‐modified Al2O3 were synthesized and characterized using powder X‐ray diffraction, nitrogen physisorption, transmission electron and scanning transmission electron microscopies, temperature‐programmed hydrogen reduction （H2‐TPR）, Raman spectroscopy, and in situ diffuse‐reflectance infrared Fourier‐transform spectroscopy. Highly dispersed Au nanoparticles and strong structures formed by Au–support in‐teractions were the main active species on the ceria surface. The Raman and H2‐TPR results show that the improved catalytic performance of the Au catalysts can be attributed to enhanced strong metal–support interactions and the reducibility caused by ceria doping. The formation of oxygen vacancies on the catalysts increased their activities in CO‐PROX. The synthesized Au catalysts gave excellent catalytic performances with high CO conversions （＆gt;97%） and CO2 selectivities （＆gt;50%） in the temperature range 80–150 ＆#176;C.

Dispersion of Active Au Nanoparticles on Mesoporous SBA-15 Materials

Chemical modification(CM)and deposition-precipitation(DP)methods were used for the dispersion of active Au nanoparticles on mesoporous silica materials in this work.XRD,TEM,N2 adsorption isotherms and UV-Vis absorption spectra were used to characterize in detail Au-SBA-15 materials prepared by the two methods. The analysis results showed that high loading(1.7%,by mass)and uniform Au nanoparticles(approximately 3 nm) were dispersed in the channels of mesoporous SBA-15 by the CM method.While for the DP method,most of Au nanoparticles with the size of 10—15nm were aggregated outside of the channels of SBA-15 and the actual loading of Au was only 0.38%(by mass).

Liquid Phase Hydrogenolysis of Biomass-derived Lactate to 1,2-Propanediol over Silica Supported Cobalt Nanocatalyst

Liquid phase hydrogenolysis of ethyl lactate to 1,2-propanediol was performed over silica supporting cobalt catalysts prepared by two different methods： precipitation-gel （PG） technique and deposition-precipitation （DP） procedure. The cobalt species （Co3O4/cobalt phyllosilicate） present in the corresponding calcined PG and DP catalysts were different as a consequence of the preparation methods, and Co--OH---Co olation and Si--O--Co oxolation molecular mechanisms were employed to elucidate the chemical phenomena during the different preparation procedures. In addition, the texture （BET）, reduction behavior （TPR and in-situ XRD）, surface dispersion and state of cobalt species （XPS）, and catalytic performance differ greatly between the samples. Because of small particle size, high dispersion of cobalt species and facile reducibility, the Co/SiO2 catalyst prepared by precipitation-gel method presented a much higher activity than the catalyst prepared by deposition-precipitation method. Metallic cobalt is assumed to be the catalytically active site for the hydrogenolysis reaction according to the catalytic results of both cobalt samples reduced at different temperatures and the structure changes after reaction.