Traditional Incipient Wetness Research Articles

Characterization and evaluation of Ag–Pt/SiO 2 catalysts prepared by electroless deposition

A series of Ag–Pt/SiO 2 catalysts have been prepared by the electroless deposition of Ag onto a Pt/SiO 2 catalyst. Results indicate that Ag deposition does not readily occur on the SiO 2 support, but is essentially restricted to the Pt surface. The Ag–Pt catalysts have been characterized by FTIR of adsorbed 12CO and 13CO, which suggest that Ag is preferentially located on Pt(111) sites rather than the more coordinatively-unsaturated corner and edge sites. Hydrogenation of 3,4-epoxy-1-butene (EpB), a multifunctional olefin, was chosen as a probe reaction. Reaction data indicate that ED-derived catalysts provide a more targeted Ag placement on the Pt surface than traditional incipient wetness catalysts. EpB conversion increased dramatically ( ∼ 3 × ) with the addition of sub-monolayer coverages of Ag on the Pt surface. Conversely, activity for propylene hydrogenation decreased with increasing Ag coverages. The enhanced EpB hydrogenation appears to be due to a Ag-induced decrease in EpB adsorption energy on surface Pt sites.

Thermally Impregnated Ni−Olivine Catalysts for Tar Removal by Steam Reforming in Biomass Gasifiers

A novel and potentially economic preparation technique, thermally impregnation (TI), was developed to incorporate catalytic active materials (i.e., Ni) onto olivine. The approach allows for the synthesis of attrition-resistant Ni−olivine catalysts. Comparative studies were performed over Ni−olivine catalysts prepared by TI and traditional incipient wetness impregnation (IWI), as well as olivine without Ni. Various characterization techniques such as BET surface area analysis, temperature-programmed reaction/oxidation/reduction, XRD, and XPS were performed to examine the catalysts. The Ni−olivine catalyst prepared by TI demonstrated improved activity and “coke selectivity” compared to the olivine support, indicating that Ni is necessary for enhanced activity. Additionally, the Ni−olivine catalyst prepared by TI showed similar high-temperature activity and decreased coke deposition rates compared to similar formulations prepared by IWI. Stronger interactions between Ni and the olivine support for the TI catalyst were responsible for the improved catalytic properties compared to IWI catalysts. Moreover, effects of pretreatment and reaction parameters such as temperature and time-on-stream (TOS) were studied. The reaction network in simulated biomass-derived syngas was also investigated to probe the possible reactions occurring in a biomass gasifier. The Ni−olivine catalyst prepared by TI possessed catalytic activity for several reactions such as the water gas shift (WGS), reverse WGS, methanation, and Boudouard reactions.

Sonochemically Prepared Pt/CeO2 and Its Application as a Catalyst in Ethyl Acetate Combustion

Highly dispersed Pt nanoparticles were incorporated in CeO2 nanopowders by an ultrasound-assisted reduction procedure. The activity of the Pt/CeO2 catalysts was studied in the reaction of the ethyl acetate combustion, and complete conversion was achieved at low temperature. It was demonstrated that the higher dispersion of the CeO2 support, the better the performance of the Pt/CeO2 catalysts. The catalysts were characterized by XRD, TEM, HRTEM, EDX, BET, and XPS. The homogeneous incorporation of 2-4 nm Pt nanoparticles into the interparticle distance of the CeO2 nanopowders was demonstrated. The advantage of the sonochemical method for catalyst preparation, in comparison with the traditional incipient wetness impregnation, was explained as the result of the homogeneity and better dispersion of the active metal phase obtained by ultrasound irradiation.

In situ synthesis of supported palladium complexes: Highly stable and selective supported palladium catalysts for hydrodechlorination of CCl 2F 2

Supported palladium phosphine complexes [Pd(PPh 3) 2X 2/MgF 2] (X = Cl or SCN) were prepared as precursor catalysts for hydrodechlorination of CCl 2F 2 by a method of in situ synthesis of palladium complex on support (ISPS) and using environmentally benign solvents. Their performance and activities were compared to those of catalysts prepared via traditional incipient wetness impregnation method by catalytic reaction and characterization results, including FT-IR, XPS, XRD and H 2-chemisorption. After an induction period, during which the Pd(II) precursors are converted to active species by being put in contact with substrate CCl 2F 2 and H 2, stable catalytic activities and improved selectivities to CH 2F 2 (>93% on Pd(PPh 3) 2(SCN) 2/MgF 2) are achieved. The improvement of catalytic performance was ascribed to the more homogenous distributing of catalyst precursor on the surface of the support, where the amounts of the sites that induce side reactions are decreased. The XPS results revealed that there exist two kinds of active Pd sites on the surface of catalysts. One is Pd(0) site for the activation of hydrogen, and the other is the Pd site of high electrovalence, i.e. electron-deficient palladium for the activation of CCl 2F 2. High dispersion (∼90%) of Pd particles results in a strong interaction between Pd and the support, and creates electron-deficient palladium sites being of high selectivity to CH 2F 2.

Dimethyl carbonate production via the oxidative carbonylation of methanol over Cu/SiO 2 catalysts prepared via molecular precursor grafting and chemical vapor deposition approaches

The influence of catalyst synthesis method and Cu source on the activity and selectivity of Cu/SiO 2 catalysts for the gas-phase oxidative carbonylation of methanol to dimethyl carbonate (DMC) is reported. [CuOSi(O t Bu) 3] 4, [CuO t Bu] 4, and CuCl were used as precursors to produce highly dispersed silica-supported copper. XANES and EXAFS characterization prior to reaction (but after thermal treatment under He) showed that Cu in the catalysts prepared with CuCl and [CuOSi(O t Bu) 3] 4 was present primarily as isolated Cu(I) species, whereas [CuO t Bu] 4 produced 1-nm Cu particles. During the catalytic reaction, the Cu in catalysts prepared from CuCl and [CuOSi(O t Bu) 3] 4 formed highly dispersed CuO moieties, whereas the Cu in catalysts prepared from [CuO t Bu] 4 formed a cuprous oxide layer over a Cu(0) core. For comparison, poorly dispersed Cu on silica was prepared via traditional incipient wetness impregnation with Cu(NO 3) 2. It was found that activity for DMC formation increased with increasing Cu dispersion. The selectivity for DMC formation (relative to CO) decreased with decreasing Cu dispersion when the original state of the Cu was Cu(0) directly preceding reaction conditions.

Structure Control of Metal Aluminum Phosphate (MeAlPO-5) Molecular Sieves and Applications in Polyethylene Glycol Amination

The structure and morphology of both pure AlPO-5s and nickel containing AlPO-5s were affected by the preparation conditions such as pH value, nickel incorporated method (hydrothermal method or traditional incipient wetness impregnation). The dense tridymite phase of AlPO-5 can be formed by two controlling factors. One is controlling the pH at lower value to the AlO4 and PO4 moleculars to form AlPO4 with dense phase, and the other is used the excess nickel adding to increase the crystallinity of AlPO-5 to form dense tridymite phase. The reactivity of PEG-400 amination was also affected preparation methods and conditions. At higher nickel loading, the nickel supported on AlPO-5 prepared by traditional incipient wetness impregnation forms the surface nickel species, and both the surface nickel species and nickel incorporated species form by the hydrothermal method. The amination catalysis indicates that the reactivity of PEG-400 prepared by incipient wetness impregnation method was higher than that prepared by hydrothermal method. The formation of the dense tridymite phase of AlPO-5 can be further determined by the X-ray powder diffraction (XRD). The nickel containing AlPO-5s prepared with lower pH value possesses only the tridymite phase and exhibit higher catalytic reactivity. It appears that the trydimite structure can improve the catalytic activity for PEG-400 amination due to the grain size of the formed crystal of NiAlPO-5 is smaller than the catalyst without the formation of the trydimite phase.