Characterization and catalytic performance of Au/Ti-HMS for direct generation of H2O2 and in situ-H2O2-ODS from H2 and O2: An in situ-reduction synthesis and a recycle study of catalyst

Ti-HMS supported gold catalyst (Au/Ti-HMS) has been synthesized by an in situ-reduction method using NaBH4 as reducing agent for Au3+. The samples were characterized by a series of techniques including ICP, powder XRD, UV-vis spectroscopy and TEM. Catalytic performance of this bifunctional catalyst was tested in the direct synthesis of H2O2 from H-2 and O-2 and the oxidative desulfurization using H2O2 generated in situ (in situ-H2O2-ODS). The results show that the optimum catalyst possesses uniform gold nanoparticles (4 nm) embedded between the channels of the support. The average size of gold particles increases as the NaBH4/Au molar ratio increases. Addition of HCl during Au/Ti-HMS synthesis contributes to maintaining the structure of HMS. As NaBH4/Au molar ratio of the catalyst increases from 1.25:1 to 15:1, in the reaction of in situ-H2O2-ODS the final removal rates of BT and DBT decrease from 100% to 56.5% and 75.8%, respectively. The 2 Au wt.% in situ-reduction sample gives high productivity of H2O2 (27 mol H2O2 h(-1) kg Au-1), as well as good durability (over 5 recycles). In contrast, the previous 4 Au wt.% in situ sample only generates 6 mol H2O2 h(-1) kg Au-1, and is seriously inactivated after being used 2 cycles because of the loss of gold. The in situ-reduction sample can be reused for more than 5 cycles in the in situ-H2O2 oxidations of BT and DBT, and almost 100% removal of sulfur can be obtained in each recycle. But the deactivation becomes dominant in oxidation of 4,6-DMDBT. (c) 2010 Elsevier Inc. All rights reserved.