Hydrogen production from natural gas on new alumina-based catalysts

Abstract

Rising global energy demand together with accelerated concerns of global warming have urged ongoing-research in finding efficient alternative energy resources and carriers. Methane conversion into hydrogen or synthesis gas offers promising potential for generation of alternative clean energy carriers. In this work, methane conversion via chemical looping partial oxidation (CLPO) or via catalytic methane decomposition (CDM) was investigated over a series of novel mesoporous systems composed mainly of iron species deposited inside alumina matrices. Different approaches were investigated for the preparation of stable and efficient catalysts. The first route consisted of synthesis and evaluation of MIL-53 (Fe, Al) materials, as sacrificial structuring agents, for subsequent production of mesoporous Fe-Al-catalysts. A series of complementary characterizations of MIL-53(Fe, Al), with various Fe loadings, were conducted for a better understanding of their physico-chemical properties. Notably, Powder X-ray diffraction (PXRD), diffuse-reflectance infrared spectroscopy (DRIFTS), Raman spectroscopy, thermogravimetry (TGA), N2 physisorption and, scanning electron microscopy (SEM). Combined data from all characterizations reveal the successful synthesis of isomorphic MIL-53(Fe, Al) analogues, thus making them eligible and highly promising candidates for CDM catalysis; a robust tactic never considered previously in the available literature. The second approach entailed the synthesis of Fe-Al mesoporous materials via a "one-pot" inspired evaporation-induced self-assembly strategy. For the sake of comparison, catalysts with various transition metals (i.e. Ni, Cu, Co and Mn) were synthesized. Catalysts reveal selective conversion of methane into syngas under chemical looping partial oxidation conditions. Moreover, the screening of the various metals for COx-free hydrogen and carbon productions via CDM reveals that iron stands out as an economically and environmentally attractive active site for this reaction. The activity increases with increase in Fe loading (passing from 20 to 50 wt%), while preserving the mesoporous arrangement of the catalyst. Fe50%Al2O3 shows an outstanding hydrogen yield of 96% and a selective generation of (non-deactivating) carbon nanotubes making it a highly efficient and a promising catalyst for industrially-oriented methane decomposition operations.