Abstract
In this study, NiO/SBA-15 was prepared by both direct and post synthesis methods. TEM images revealed that NiO particles aggregated in NiO/SBA-15 obtained with post synthesis method, regardless of NiO loading. However, NiO particles were monodispersed in NiO/SBA-15 with a NiO loading of less than 15 wt% by using the direct synthesis method. In this case, NiO particles aggregated when NiO loading was over 20 wt%. TPR analysis verified that with direct synthesis method the location boundary of NiO particles on outer and pore surface could be observed clearly, whereas that could not observed in the case of post synthesis method. This indicates that the type of synthesis method displays significant effect on the location of NiO particles dispersed into the SBA-15. Producer gas conversion was carried out using NiO/SBA-15 as catalysts, which were synthesized with different synthesis methods. The gas conversion including methanation occurred at low temperature (i.e., 300–400 °C) and the reverse water gas shift (RWGS) reaction at high temperature (i.e., 400–900 °C). High temperatures facilitated CO2 conversion to CO with CO selectivity close to 100 %, regardless of the synthesis method of the used catalyst. At low temperatures the dispersion type of NiO particles affected the CO2 conversion reaction, i.e., monodispersed NiO particles gave a CO selectivity of close to 100 %, similar to that obtained at high temperature. The aggregated NiO particles resulted in a CO selectivity of less than 100 % owing to CH4 formation, regardless of synthesis method of catalyst. Therefore, NiO/SBA-15 obtained with direct synthesis method favored RWGS reaction because of high CO selectivity. NiO/SBA-15 obtained with post synthesis method is suited for methanation because of high CH4 selectivity, and the conversion of CO2 to CH4 through methanation increased with increasing NiO loading.
Highlights
As an important energy resource for replacing petroleum, coal and biomass have attracted great interest
NiO/SBA-15 obtained with post synthesis method is suited for methanation because of high CH4 selectivity, and the conversion of CO2 to CH4 through methanation increased with increasing NiO loading
The wide-angle XRD peaks could be indexed to a face-centered cubic crystalline NiO structure, irrespective of synthesis method (Fig. 1b), indicating that NiO particles were dispersed on the outer surface besides on pore surface of SBA-15
Summary
As an important energy resource for replacing petroleum, coal and biomass have attracted great interest. Gasification is an important process as regards to the utilization of them in energy recycling, namely, converting into a producer gas mixture consisting of carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2) and other trace species (Huber et al 2006; Zhu et al 2008; Yung et al 2009). Nickel(Ni)-based catalysts remain the most extensively studied well-dispersed materials, and Ni-based catalysts have been investigated for the RWGS reaction and methanation (Vance and Bartholomew 1983; Wang et al 2008). We synthesized NiO/SBA-15 with 10 wt% NiO using direct and post synthesis methods, respectively Their TEM observations were carried out to investigate the dispersion of NiO particles in SBA-15. The RWGS reaction and methanation were carried out using NiO/SBA-15 obtained with different synthesis methods and NiO loadings
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