Effect of preparation parameters on the gold particle size of Au/HZSM-5

A serial of Au/HZSM-5 samples were prepared by vacuum deposition precipitation, cation exchange and vacuum sulfhydryl protection method. The effect of different preparation method, calcination temperature, calcination atmosphere and addition of potassium on the particle size and distribution of gold was invetigated. Based on the characterization of X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy and transmission electron microscope, it was found that the gold particle size of Au/HZSM-5 was changed greatly with different preparation methods. Gold particle size (about 2-5nm) of Au/HZSM-5 prepared by vacuum sulfhydryl protection was obviously smaller than that of the other preparation methods. Taken Au/HZSM-5 catalyst prepared by vacuum deposition precipitation as an example, low calcination temperature and inert atmosphere (nitrogen and argon) were favorable to the good dispersion of gold particles. The activities and carbonylation selectivities of syngas on Au/HZSM-5 catalysts were evaluated by a micro-fixed pulse reactor. 48% of syngas conversion and 52% of methyl acetate selectivity were obtained at reaction temperature of 350℃ over Au/HZSM-5 catalysts with 1.86% Au loading, calcined in air, while 59% and 70% were obtained over catalyst calcined in argon. By contrast, 67% of syngas conversion and 78% of methyl acetate selectivity were obtained over the catalyst calcined in nitrogen plasma.