Copper mesoporous materials as highly efficient recyclable catalysts for the reduction of 4-nitrophenol in aqueous media

Abstract

Two mesoporous-based catalysts with different nominal copper loads (10 and 24% w/w) were prepared from impregnation of the MCM-41 support with copper acetylacetonate: Cu/MCM-41-10 and Cu/MCM-41-24, respectively. Samples with a metallic charge similar to the nominal content were obtained and the mesoporous structure was retained after the impregnation. X-ray diffractograms evidenced the presence of CuO in the catalyst with the higher metal loading. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in aqueous medium, with an excess of NaBH4, was chosen as a model reaction to evaluate the catalytic activity of the Cu/MCM-41-10 and Cu/MCM-41-24 catalysts. The 4-NP concentrations at prefixed intervals were monitored using UV–Vis spectroscopy. The Cu-based catalysts led to almost 100% reduction of 4-NP to 4-AP, with the reaction time of 30 and 50 s, for Cu/MCM-41-10 and Cu/MCM-41-24 respectively. The reaction follows a pseudo-first order law, with a rate constant of 0.374 and 0.109 s−1 for Cu/MCM-41-10 and Cu/MCM-41-24, respectively. Both catalysts were stable and could be reused up to ten times in consecutive runs without any treatment between the cycles. The catalytic activity was retained without loss of efficiency, indicating the high stability of the MCM-41 based catalysts under the reaction conditions.