On the mechanism of oxidative degradation of rhodamine B over LaFeO3 catalysts supported on silica materials: Role of support

• Effect of silica supports on the catalytic performances of LaFeO3 for RhB oxidation is investigated.
• The use of porous silica is essential in promoting the activity of LaFeO3 for RhB oxidation.
• The property of pores of silica influences greatly on the activity of LaFeO3 for RhB oxidation.
• The RhB oxidized on LaFeO3 comes not directly from the solution, but from that adsorbed on the support.
• A mechanism for RhB oxidation over LaFeO3/Silica composites is proposed.

This work aims to investigate the role of silica support in the catalytic oxidation of rhodamine B (RhB) over LaFeO3-Silica composites. Four LaFeO3-Silica composites using mesoporous silica (SBA-15, SBA-16, MCF) and nano-sized silica powder (NSP) as supports are prepared. XRD, N2 physisorption isotherms and TEM results show that pure LaFeO3 phase, with particle size of 15–20 nm, is prepared and the texture of supports remains unchanged after the deposition of LaFeO3. Catalytic results show that, besides the function to disperse LaFeO3 on the surface, the support plays two important roles in the reaction: one is to absorb RhB from solution to its pores, and the other is to transport RhB from the pores to the active site, both influence the catalytic efficiency. Thus the non-porous NSP with negligible capacity for RhB adsorption is the worst, and the porous MCF with considerable capacity for RhB adsorption and the strongest ability for RhB transportation is the best support of LaFeO3 for RhB oxidation. SBA-15 and SBA-16, although show considerable or even higher capacity for RhB adsorption relative to MCF, their contribution to the reaction is less due to the low efficiency of transporting RhB from the pores to the active site. On these bases, the role of silica support in RhB oxidation conducted over LaFeO3-Silica composite is proposed.

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