Biogas reforming over La-NiMgAl catalysts derived from hydrotalcite-like structure: Influence of calcination temperature

Abstract

Hydrotalcite-like compound with general formula [M(II)1 − xM(III)x(OH)2]x+(An−x/n) · mH2O, where An− is the compensation anion, has been used as precursor of active catalysts for biogas reforming. This precursor was calcined at six different temperatures between 250 and 750 °C and the resulting catalysts were tested in order to evaluate the influence of the calcination temperature on the catalytic activity and stability. XRD characterization showed that from 250 °C the hydrotalcite structure is no longer detected, leading to Mg(Ni,Al)O solid solutions, where no peaks related to lanthanum appear. An increase on the calcination temperature increased the grain size and cell parameter value. 50 h-catalytic tests were carried out at 700 °C, CH4:CO2 molar ratio of 1:1 and a mass/feed alimentation ratio (W/F) of 0.4 mg min cm− 3. Used catalysts were characterized by temperature programmed oxidation (TPO), scanning electron microscopy (SEM) and Raman spectroscopy in order to obtain information about coke deposition. Catalytic tests highlighted the great influence of calcination temperature over catalytic activity and stability, having found that, as a general trend, calcination temperatures below 750 °C decrease both the stability and catalytic activity, with the exception of the catalyst calcined at 550 °C, where a higher activity was achieved but with a comparatively low stability.