Towards biofuel combustion with an easily extruded clay as a natural catalyst

The present work aims to investigate an innovative application of natural clay as a catalyst for biofuel combustion. The mineralogical, chemical, thermal and textural characterizations of the natural clay suggest an intrinsic catalytic potential without any prior treatment. The catalytic performance was studied with respect to the combustion of n-butanol as a representative biofuel using different forms of the natural clay: fine powder, pressed pellets and extruded honeycomb monoliths. No major difference was found among these forms regarding texture, morphology and stability. In terms of performance, this clay proved competitive relative to cobalt oxide spinel, which is one of the most reactive non-noble transition metal oxides. The significant amount of naturally occurring transition metals such as iron and some elements considered as promoters in the clay were proposed to account for the catalytic properties. A systematic investigation of the catalytic performance of the clay as a function of the equivalence ratio and of the total flow rate was performed using gas-phase FTIR spectroscopy. Increase of the equivalence ratio at a fixed flow rate yielded a lower catalytic performance toward n-butanol combustion producing a consequent fraction of carbon monoxide and ethylene. At a constant equivalence ratio of 0.6, the performance of the clay was not affected by increasing the total inlet flow rate up to 30sccm. These findings may initiate the development of a new catalyst for biofuel combustion based on relatively low-cost and abundantly available raw materials such as the natural clay investigated here.