Abstract
Nickel iron oxide (NiFe2O4) catalyst was prepared by the combustion reaction method and characterized by XRD, N2 adsorption/desorption, thermogravimetric analysis (TG), and temperature programmed reduction (TPR). The catalyst presented a mixture of oxides, including the NiFe2O4 spinel and specific surface area of 32.4 m2 g−1. The effect of NiFe2O4 catalyst on the supercritical water gasification (SCWG) of eucalyptus wood chips was studied in a batch reactor at 450 and 500 °C without catalyst and with 1.0 g and 2.0 g of catalyst and 2.0 g of biomass for 60 min. In addition, the recyclability of the catalyst under the operating conditions was also tested using recovered and recalcined catalysts over three reaction cycles. The highest amount of H2 was 25 mol% obtained at 450 °C, using 2 g of NiFe2O4 catalyst. The H2 mol% was enhanced by 45% when compared to the non-catalytic test, showing the catalytic activity of NiFe2O4 catalyst in the WGS and the steam reforming reactions. After the third reaction cycle, the results of XRD demonstrated formation of coke which caused the deactivation of the NiFe2O4 and consequently, a 13.6% reduction in H2 mol% and a 5.6% reduction in biomass conversion.
Highlights
Hydrogen gas is an excellent energy-carrier, which can be combusted directly or used in fuel cells without any direct carbon emissions
It is known that the temperature and fuel effects have strong influence on purity, size, structural, and magnetic properties of materials prepared by combustion route [35,36]
The presence of small agglomerates with porous aspects can be seen on the surface of a larger agglomerate and this is characteristic of de-agglomerated materials. This is due to the high temperatures attained by the combustion reaction during the synthesis of the catalyst, leading to agglomerated nanometric particles [22]
Summary
Hydrogen gas is an excellent energy-carrier, which can be combusted directly or used in fuel cells without any direct carbon emissions. The choice of catalyst to gasify lignocellulosic biomass in supercritical water depends on its ability to lower the activation energies involved in the breaking of C-C and C-O bonds in biomass, accelerate the rate of water–gas shift reaction [1,2,4] and maintain its catalytic and structural stability under hydrothermal conditions. Both homogeneous [5,6,7] and heterogenous catalysts [8,9,10]. Such sets of data will be important for further optimisation of the catalyst and the catalytic process in future
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