Search

Partial oxidation of ethanol to acetaldehyde was carried out over gold catalysts supported on various oxides and zeolites by deposition precipitation. The special focus of this work was on the influence of H-Y zeolite surface charge on Au cluster size and loading linking it to activity and selectivity in ethanol oxidation and comparing with other studied catalysts. The catalysts were characterized by nitrogen physisorption, transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDXA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and zeta potential measurements. pH of the solution governed the Au NPs size within the range of 5.8–13.2 nm with less negatively charged surfaces leading to formation of smaller clusters. Au loading on H-Y zeolite with silica to alumina ratio of 80 was increased by raising the pH. In fact, H-Y-12 and H-Beta-25 were selective towards diethyl ether while acetaldehyde was the prevalent product on less acidic H-Y-80. The results demonstrated strong dependency of the catalytic activity on the Au cluster size. Namely turn over frequency (TOF) decreased with an increase in metal size from 6.3 to 9.3 nm on H-Y-80. Selectivity towards acetaldehyde and ethyl acetate did not change significantly on H-Y-80 within 6.3–9.3 nm Au particle size range. On Al 2 O 3 support, however, selectivity towards acetaldehyde increased considerably upon diminishing Au average particle size from 3.7 to 2.1 nm. [ABSTRACT FROM AUTHOR]

Sulfur-free Ni supported on H-Y zeolites, γ-Al 2 O 3 and SiO 2 synthesized by the wet impregnation method, and Pd/C were tested in hydrodeoxygenation (HDO) of stearic acid. The catalysts were forming n- heptadecane except Ni/H-Y-80, which was producing n- heptadecane and n- octadecane. Ni/H-Y 80 and Pd/C were tested on HDO of fatty acid methyl esters from chlorella, tall oil fatty acids, and animal fat. The reactions converting the substrates to the final products followed the path from unsaturated esters to acids, with hydrogenation of the latter into alcohols (i.e., stearyl alcohol), and finally formation of hydrocarbons. Ni/H-Y-80 permitted rapid and complete conversion into hydrocarbons, while Pd/C displayed 5–20 times lower turnover frequency, producing saturated intermediates along with hydrocarbons. The catalyst reusability of Ni supported on Y zeolites was studied by recycling and regenerating the spent catalyst from fatty acid HDO. The catalysts demonstrated the possibility of restoring the rates per unit of surface area after regeneration. Catalysts used in HDO of different feedstocks were investigated by thermogravimetric analysis, inductively coupled plasma-optical emission spectroscopy, transmission electron microscopy, surface area measurements, and pore size analysis. [ABSTRACT FROM AUTHOR]

A potentiometric acid–base titration method was developed to characterize the acid–base properties of H-Beta-25, H-Beta-300, H-Ferrierite-20 and Si-MCM-48 zeolites in aqueous solutions. The method is based on linearization of the titration curve. The zeolite powders were dispersed in a sodium nitrate solution which was then titrated with a standard solution of sodium hydroxide. Various acid sites were found in the studied zeolites, and both the protonation constants and the concentrations of these acid sites were determined. The chemical composition (aluminum and silicon), distribution of the aluminum sites, crystallinity as well as the acidic properties of the titrated zeolites were compared with those of the pristine zeolites by using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), X-ray Diffraction (XRD), 27 Al NMR spectroscopy and the commonly used gas phase Fourier Transform Infrared spectroscopy (FTIR) of pyridine adsorption method. [ABSTRACT FROM AUTHOR]