Application of microemulsion method for development of methanol steam reforming Pd/ZnO catalysts

Abstract

Thermal decomposition of palladium acetylacetonate adsorbed on zinc oxide (ZnO), and the formation of palladium oxide (PdO) and palladium zinc alloy (PdZn) phases were studied. Two types of ZnO supports were prepared by the microemulsion method using different surfactants, i.e. hexadecyltrimethylammonium bromide (CTAB) and (Bis(2-ethylhexyl) sulfosuccinate sodium salt, AOT). The nanoparticles of ZnO synthesized in the presence of CTAB surfactant showed higher specific surface area, smaller crystallite size and more irregular shape. Palladium was loaded on the surface of obtained supports by the impregnation method from the acetone solution of palladium acetylacetonate. Thermogravimetric studies indicated that palladium precursor loaded on CTAB-modified ZnO support was less stable and simultaneously decomposed in broader range of temperatures. Slight differences between the forms of precursors adsorbed on the supports were demonstrated by the diffuse reflectance infrared Fourier transform spectroscopy studies. Thermal decomposition of palladium acetylacetonate precursors in the air led to the formation of PdO species. The influence of ZnO morphology on the metal–oxygen bonds strength in PdO and formation of active phases were observed. Strongly dispersed PdZn crystallites on ZnO supports were formed upon reduction at 350 °C. Smaller crystallites of the size equal to 6.5 nm were detected in the Pd/ZnO-AOT catalysts.