Preliminary results on the role of the deposition of small amounts of ZrO2 on Al2O3 support on the partial oxidation of methane and ethane over Rh and Ni supported catalysts

Abstract

Alumina supported samples have been prepared by impregnation of the support with a solution of zirconium isopropoxide in n-propanol to obtain after calcination a theoretical monolayer of zirconia (1ZrAl). The formation of a layer of tetragonal zirconia crystals over alumina was observed. Catalysts were evaluated in the partial oxidation of methane (CPOM) and ethane(CPOE) and characterized by elemental chemical analysis, BET specific surface area, X-ray diffraction, X-ray photoelectron spectroscopy and hydrogen chemisorption.The impregnation with Ni and Rh maintains this layer of tetragonal ZrO2, although microcrystals with a local distorted tetragonal environment around the Zr have probably been formed as inferred by the broadness of the XRD zirconia peaks.Different Zr environments and different charge densities on the Zr sites are detected after the test in CPOM and CPOE in Ni/1ZrAl and Rh/1ZrAl catalysts. After the tests in CPOM and CPOE, no ZrO2 peaks are detected in Ni/1ZrAl, which indicates that the ZrO2 layer is either amorphous or formed by ZrO2 nanocrystals. On the other hand, a slight interaction between zirconia and alumina is observed, which leads to an increase in the positive charge density on the Zr. In the case of Rh/1ZrAl after both tests, a layer of distorted tetragonal zirconia microcrystals and no interaction between zirconia and alumina are detected. Catalytic tests in CPOM and CPOE make it possible to determine that the modified support improves significantly the performances of the catalysts. The variation in the local environment of the Zr sites and in its charge density favor the adsorption of intermediates/reaction products at high temperatures on the Zr sites, particularly in the amorphous state, which leads to an enhancement in hydrogen production through STRM and Dry reforming of methane.