The use of mixed γ- and χ-phase Al2O3 as supports for preparation of Pt/Al2O3 catalysts resulted in higher acidity of Al2O3 and higher Pt dispersion compared to the pure phase supports. As a consequence, higher propane oxidation activities were
Authors:Kanda Pattamakomsan, Francisco Jose Cadete Santos Aires, Kongkiate Suriye, and Joongjai Panpranot
Pd/Al2O3 catalysts prepared from Pd nitrate dissolved in water (Pd-water) and toluene (Pd-toluene) were investigated in the gas-phase selective hydrogenation of 1,3-butadiene under various reaction conditions. As revealed by TEM and CO chemisorption results, smaller Pd particle sizes with more uniform particle size distribution were obtained on Pd-toluene catalysts. Reduction at 500 °C resulted in sintering of Pd particles with Pd-water showing higher degree of metal sintering than Pd-toluene. Sintering of Pd particles may result in low-index surfaces which promoted butane formation and lowered 1-butene selectivity. While Pd dispersion and/or Pd particle size strongly affected 1,3-butadiene hydrogenation rate and 1-butene selectivity, the selectivity to 2-butenes was quite similar at 47–55% for all the catalysts under various reaction conditions.
La-modified ZrO2 with 10 mol% La was prepared by three different methods, namely co-precipitation, impregnation, and mechanical mixing and employed as cobalt catalyst supports. The use of La-modified ZrO2 prepared by mechanical mixing resulted in higher cobalt dispersion and higher CO hydrogenation activity than those supported on pure oxide (La2O3 and ZrO2) and La-modified ZrO2 obtained by the other methods. As revealed by XRD and TEM, an intimate contact and/or incorporation of La atoms in ZrO2 may occur on the La-modified ZrO2 prepared by co-precipitation and impregnation, which induced a stronger interaction between cobalt and the support. On the other hand, the presence of amorphous La2O3 in ZrO2 by mechanical mixing facilitated cobalt reducibility as shown by lower reduction temperature in the TPR profile.
The properties of Co/Al2O3 catalysts prepared by the solid-state reaction between gibbsite and various cobalt salts such as cobalt acetate (CoAc), cobalt acetylacetonate, cobalt chloride, and cobalt nitrate (CoNT) were investigated in the hydrogenation of carbon dioxide at 270 °C and atmospheric pressure and characterized by N2 physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, and H2-temperature programmed reduction. Compared to the catalyst prepared by conventional impregnation of aqueous solution of cobalt nitrate on alumina (CoNT-Imp), the solid-state catalysts (CoNT and CoAc) exhibited much higher activity in the CO2 hydrogenation with comparable CH4 and CO selectivity. Unlike the impregnation catalysts, in which most of the Co3O4 particles/clusters were located deep inside the pores of alumina, the solid-state reaction resulted in the dispersion of cobalt oxides mostly on the external surface of alumina. As a consequence, CO2 adsorption and dissociation to adsorbed CO and O (the initial steps in CO2 hydrogenation) were not limited by the slow diffusion of CO2 so high CO2 hydrogenation activity was obtained. As revealed by the XRD and H2-TPR results, the average crystallite size of Co3O4 and the metal-support interaction depended on the cobalt precursor used during the solid-state synthesis. Nevertheless, the solid-state reaction of gibbsite and cobalt chloride at 650 °C resulted in very poor CO2 hydrogenation activity due to the formation of inactive cobalt aluminate.