Investigation of the effect of metal sites in Me–Al-MCM-41 (Me = Fe, Cu or Zn) on the catalytic behavior during the pyrolysis of wooden based biomass

The mesoporous material Al-MCM-41 has previously been reported to exhibit interesting catalytic properties during the pyrolysis of wooden based biomass. In this work, four materials with Si:Al ratio of 20, have been investigated, a parent Al-MCM-41 and Me–Al-MCM-41 (Me being Fe, Cu and Zn). The materials have been fully characterized in order to obtain structural information about the local metal surroundings, by XRD, nitrogen absorption isotherms, 27Al-MAS-NMR and XAS. Results have shown that the metal sitings are different in these materials, in that iron is tetrahedrally coordinated, substituting for aluminium in the walls of the mesoporous material, while copper is present as an extra phase, forming CuO upon calcination. The EXAFS-spectra for Zn–Al-MCM-41 have shown that the material remains unchanged upon calcination, with no sintering of zinc, indicating a framework siting. However, two Zn…Si distances show a higher degree of disorder than in the iron-containing sample. The catalysts are all shown to improve the product distribution and the quality of the bio-oil with respect to the yield of phenols. The presence of Zn–Al-MCM-41 as the catalyst leads to the lowest yield of phenols, but this catalyst gives the best results with respect to reduction of coke produced. The investigations have shown that these mesoporous materials are promising catalysts for the pyrolysis of biomass, and that the type of metal is of more importance than the metal siting.