Water-assisted oxidative redispersion of Cu particles through formation of Cu hydroxide at room temperature.

Sintering of active metal species often happens during catalytic reactions, which requires redispersion in a reactive atmosphere at elevated temperatures to recover the activity. Herein, we report a simple method to redisperse sintered Cu catalysts via O2-H2O treatment at room temperature. In-situ spectroscopic characterizations reveal that H2O induces the formation of hydroxylated Cu species in humid O2, pushing surface diffusion of Cu atoms at room temperature. Further, surface OH groups formed on most hydroxylable support surfaces such as γ-Al2O3, SiO2, and CeO2 in the humid atmosphere help to pull the mobile Cu species and enhance Cu redispersion. Both pushing and pulling effects of gaseous H2O promote the structural transformation of Cu aggregates into highly dispersed Cu species at room temperature, which exhibit enhanced activity in reverse water gas shift and preferential oxidation of carbon monoxide reactions. These findings highlight the important role of H2O in the dynamic structure evolution of supported metal nanocatalysts and lay the foundation for the regeneration of sintered catalysts under mild conditions.

Synthetic Fuels from Biomass: Photocatalytic Hydrodecarboxylation of Octanoic Acid by Ni Nanoparticles Deposited on TiO2.

Decarboxylation of low-value fatty acids from biomass is a simple process to produce synthetic fuels suitable to be blended with gasoline or diesel. The present study reports the photocatalytic decarboxylation of octanoic acid in the presence of H2 by a series of modified TiO2 to form mixtures of n-heptane and tetradecane as major products in variable proportions, depending on the photocatalyst and the reaction conditions. It was found that the photocatalytic activity increases upon an optimal reductive NaBH4 treatment, presumably by generation of surface oxygen vacancies and by the deposition of Ni nanoparticles in the appropriate loading. Under the optimized conditions, an almost complete octanoic acid conversion and a combined selectivity to n-heptane and tetradecane over 80 % were reached at 10 h of UV/Vis light irradiation with a 300 W Xe lamp. No changes in the photocatalytic performance were observed for six consecutive runs. The present results illustrate the possibility that photocatalytic decarboxylation offers for the transformation of biomass into synthetic fuels under mild conditions.

Synergistic effect of Cu and Fe small nanoparticles supported on porous N-doped graphitic framework for selective electrochemical CO2 reduction at low overpotential.

Electrochemical CO2 reduction is an appealing approach to diminish CO2 emissions, while obtaining valuable chemicals and fuels from renewable electricity. However, efficient electrocatalysts exhibiting high selectivity and low operating potentials are still needed. Herein it is reported that Cu and Fe nanoparticles supported on porous N-doped graphitic carbon matrix are efficient and selective electrocatalysts for CO2 reduction to CO at low overpotentials. XRD and Raman spectroscopy confirmed independent Cu and Fe metals as the main phases. HRSEM and HRTEM images show the coral-like morphology of the porous N-doped graphitic carbon matrix supporting Cu and Fe metal nanoparticles (about 10 wt%) homogeneously distributed with an average size of 1.5 nm and narrow size distribution. At the optimum Fe/Cu ratio of 2, this material present high activity for CO2 reduction to CO at -0.3 V vs. RHE with a faradaic efficiency of 96%. Moreover, at -0.5 V vs. RHE this electrocatalyst produces 27.8 mmol of CO gcat-1 h-1, the production rate being stable for 17 h. A synergy between Cu and Fe nanoparticles due to their close proximity in comparison with independent Cu or Fe electrocatalysts was observed.

Transformation of Jatropha Oil into High-Quality Biofuel over Ni-W Bimetallic Catalysts.

The production of fuel from the hydrodeoxygenation of vegetable oils has been extensively investigated on account of the decline of petroleum-based fuels and increase of ecological problems. The conversion of jatropha oil over Al-MCM-41-supported Ni, W, and Ni-W catalysts was studied at 3 MPa and 360 °C. Over the monometallic Ni and W catalysts, the biofuel yield was low, about 19.3 and 12.5 wt %, respectively, whereas the highest biofuel yield reached 63.5 wt % over the Ni-W bimetallic catalysts. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-resolution TEM results suggested that the proper amount of Ni and W would form a Ni17W3 active phase, the particle size of which varied with the content of Ni and W or preparation methods. The crystalline Ni17W3 phase formed when the content of both Ni and W reached 10%. With further increase of the content of W or Ni to 15%, the crystal size of Ni17W3 grew from 7 to 14 nm or to 20 nm, whereas the biofuel yield decreased with the increase of the Ni17W3 crystal size. The 10Ni-10W/Al-MCM-41 catalyst with the Ni17W3 crystal size of 7 nm showed the best performance for the transformation of jatropha oil into high-grade biofuel.

Pore Size Expansion Accelerates Ammonium Bisulfate Decomposition for Improved Sulfur Resistance in Low-Temperature NH3-SCR.

Sulfur poisoning has long been recognized as a bottleneck for the development of long-lived NH3-selective catalytic reduction (SCR) catalysts. Ammonium bisulfate (ABS) deposition on active sites is the major cause of sulfur poisoning at low temperatures, and activating ABS decomposition is regarded as the ultimate way to alleviate sulfur poisoning. In the present study, we reported an interesting finding that ABS decomposition can be simply tailored via adjusting the pore size of the material it deposited. We initiated this study from the preparation of mesoporous silica SBA-15 with uniform one-dimensional pore structure but different pore sizes, followed by ABS loading to investigate the effect. The results showed that ABS decomposition proceeded more easily on SBA-15 with larger pores, and the decomposition temperature declined as large as 40 °C with increasing pore size of SBA-15 from 4.8 to 11.8 nm. To further ascertain the real effect in NH3-SCR reaction, the Fe2O3/SBA-15 probe catalyst was prepared. It was found that the catalyst with larger mesopores exhibited much improved sulfur resistance, and quantitative analysis results obtained from Fourier transform infrared and ion chromatograph further proved that the deposited sulfates were greatly alleviated. The result of the present study demonstrates for the first time the vital role of pore size engineering in ABS decomposition and may open up new opportunities for designing NH3-SCR catalysts with excellent sulfur resistance.