Intermetallic PdZn/TiO2 catalysts for methanol production from CO2 hydrogenation: The effect of ZnO loading on PdZn-ZnO sites and its influence on activity

In this work, intermetallic PdZn-ZnO catalysts supported on high surface area TiO2 were synthesized using metalorganic precursors and different Zn/Pd molar ratio (2.5, 5 and 7.5). The use of organic Pd and Zn precursors in the impregnation of TiO2 has made it possible to achieve the formation of PdO and ZnO nanoparticles that facilitate the uniform formation of small intermetallic beta-PdZn particles after reduction with hydrogen at 450 degrees C. No significant differences in formation, crystallinity or size of intermetallic PdZn particles with varying the Zn concentration were observed. The differences were in the characteristics of the ZnO particles that lead to enhanced development of the contacts between the PdZn and ZnO particles . The best methanol yield (78.9 mmolMeOH center dot min- 1 center dot molPd- 1) was obtained over the catalyst with highest ZnO content. This was consequence of the higher development of PdZn-ZnO interfaces, where CO2 adsorption and hydrogenation of intermediate species to methanol occurs, as well as of the higher stability of the largest ZnO particles under reaction conditions.