Cu state and behaviour in MCM-41 mesoporous molecular sieves modified with copper during the synthesis––comparison with copper exchanged materials

Abstract

CuAlMCM-41 and CuNbMCM-41 mesoporous molecular sieves with various Si/Cu ratios were synthesised at room temperature (RT) by the method of direct insertion of metal ions during the synthesis. The physicochemical properties of the materials have been investigated by means of XRD, N 2 adsorption/desorption, 27Al MAS NMR and 29Si MAS NMR, ESR, H 2-TPR and FTIR combined with NO or NO + NO 2 adsorption. It has been documented that H 2-TPR measurements and FTIR spectroscopic study combined with the adsorption of NO and NO + NO 2 are useful methods for the estimation of the localisation of transition metal cations (framework or extra-framework positions). The comparison of results obtained for CuMCM-41 catalysts prepared by the direct synthesis with those for copper-exchanged MCM-41 allows the statement that copper in CuMCM-41 exhibits a different state and behaviour than that in Cu-MCM-41. It could suggest that copper in CuMCM-41 materials is partially located in the skeleton. The catalytic activity was tested in the liquid phase hydroxylation of phenol. CuNbMCM-41 material presents the highest yield of hydroquinone, that is why this catalyst can be attractive material for hydroxylation with selectivity to p-product. The role of copper leaching during the liquid phase reaction in water medium is pointed out.