Catalytic properties of Cu/SBA-3 in oxidative dehydrogenation of methanol—The effect of the support composition
Silicate, niobosilicate and aluminosilicate mesoporous sieves of SBA-3 type with hexagonal arrangement of pores were synthesised and modified by the wetness impregnation with copper (1 wt% loading). The physicochemical properties of the samples were investigated by XRD, N2 adsorption–desorption, XRF, ICP, H2-TPR, ESR, UV–vis, XPS techniques and in acid-basic test reactions—acetonyloacetone cyclisation, 2-propanol reaction as well as by pyridine adsorption combined with FTIR measurements. The oxidative/dehydrogenation catalytic activity of prepared catalysts was examined in the methanol oxidation reaction. Depending on the chemical composition of the SBA-3 support, various copper species were found to be formed and a range of catalytic activities could be achieved. On SBA-3, AlSBA-3 and NbSBA-3 the following copper species were found dominant: bulk CuO, oligonuclear [Cuδ+⋯Oδ−⋯Cuδ+]n clusters and isolated copper cationic species, respectively. Migration of niobium species from the inert part of walls onto the surface after copper loading was observed. The Si/Nb ratio in the support was established to determine the activity and selectivity of Cu modified samples. By the proper combination of the content of Nb and Cu on the surface of SBA-3 materials it can be possible to obtain the catalysts selective to the desired products in oxidation of methanol. The highest production of formaldehyde from methanol was obtained on Cu/NbSBA-3-64 (Si/Nb = 57 in bulk and 43 on the surface, Nb/Cu = 0.8 on the surface).
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (135 K)Download as PowerPoint slideResearch highlights▶ Chemical composition of SBA-3 supports determines copper species loaded. ▶ NbSBA-3 favours isolated Cu2+ which chemisorb methoxy species from methanol. ▶ Nucleophilic oxygen adsorbs on anionic vacancies and abstract hydrogen from –OCH3. ▶ Cu–Nb interaction decreases strength of LAS and increases formaldehyde selectivity.
Journal: Applied Catalysis A: General - Volume 393, Issues 1–2, 15 February 2011, Pages 215–224