LDH-derived Ni–MgO–Al2O3 catalysts for hydrogen-rich syngas production via steam reforming of biomass tar model: Effect of catalyst synthesis methods

Abstract

Steam reforming of toluene (SRT) as a model tar compound is studied on Ni–MgO–Al2O3 hydrotalcite synthesized by different methods: urea hydrolysis, coprecipitation, and wet impregnation. The two wet-impregnated catalysts were produced by immersing MgO–Al2O3 hydrotalcites synthesized by urea hydrolysis and coprecipitation in Ni2+ solution to produce the corresponding impregnated catalysts. Among all the catalysts, both the samples prepared by urea hydrolysis gave superior toluene conversion of ~85% and also improved the resistance to carbon deposits. The two coprecipitation catalysts had a low toluene conversion of ~63% and also produced more coke. The X-ray photoelectron spectroscopy studies showed that impregnated catalyst produced from urea hydrolysis imparted greater metal-support interaction; whereas the coprecipitation impregnation catalysts only weakly interacted with the support. The CO2 temperature programmed desorption measurement of the reduced catalysts showed that urea hydrolysis catalysts possessed higher surface basicity as compared to coprecipitation catalysts. This high basic character aided in suppressing the coke formation. HRTEM results also revealed that urea hydrolysis produced smaller Ni0 particles (6–7 nm) and coprecipitation produced larger particles (10–20 nm). The excellent reforming properties of urea hydrolysis is due to smaller Ni0 particle size and greater surface basicity which aided in improving the catalytic performance and suppressing coke.