Modifications induced by pretreatments on Au/SBA-15 and their influence on the catalytic activity for low temperature CO oxidation

Abstract

SBA-15 functionalization with mercaptopropyltrimethoxysilane has been used to prepare supported gold catalysts for the low temperature CO oxidation reaction. Supports and catalysts have been characterized by chemical analysis, CHS analysis, XRD, TGA, nitrogen adsorption-desorption at 77 K, TEM, CPMAS NMR, XPS and EPR. Catalytic runs have been carried out at atmospheric pressure and 313-623 K and the influence of diverse thermal treatments of the samples prior to reaction has been investigated. The presence of organic residues and the size of the gold nanoparticles strongly affect catalytic activity. Only high-temperature calcination in air followed by treatment under H2 atmosphere leads to active catalysts. After complete elimination of the functionalizing agent, caused by the calcination step, a gold-mediated "activation" process of the silica support takes place during the hydrogen treatment. As a consequence, active catalysts for the low temperature CO oxidation are obtained, even though the size of the Au particles is too large for establishing direct Au-oxygen interactions, usually assumed to be essential for the reaction over silica-supported gold catalysts.

Mesostructured Au/C materials obtained by replication of functionalized SBA-15 silica containing highly dispersed gold nanoparticles

“…2a). Results of the literature have shown that the BET surface area and pore volume slightly decreased upon grafting but that the pore diameter remained almost unchanged [30,31].…”

“…SBA-15 was then functionalized with two different types of molecules: N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TPTAC, ABCR 50 wt.% in MeOH) or mercaptopropyltrimethoxysilane (MPTMS, Aldrich). These two molecules have been successfully used to obtain gold nanoparticles within the pores of SBA-15, with excellent dispersion and average diameter below 5 nm [30,31].…”

Catalysis by gold: New insights into the support effect

“…It has been reported that the hydroxyls on the surfaces of silica can be activated by Ag [149] or Pt [150,151]. Electron paramagnetic resonance (EPR) results also showed that there were defects that can help to activate the reactants after the Au/SBA-15 catalysts were reduced under hydrogen atmosphere at high temperatures [121,152]. Thus, irreducible silica might be more than a spectator for the reaction after proper pretreatment (e.g., reduced by H 2 , treated by water, etc.)…”

Synthesis of Gold Catalysts Supported on Mesoporous Silica Materials: Recent Developments

“…Rombi et al [61] functionalized SBA-15 with MPS by co-condensation using a TEOS:MPS molar ratio of 10, and after surfactant removal by Soxhlet extraction with a mixture of ethanol and HCl, gold (3%wt) was loaded using HAuCl 4 as precursor. Once the solution became colorless, indicating the deposition of gold on the SBA-15 surface, sodium citrate was poured into the mixture to reduce the Au 3+ to Au + species.…”