Novel catalyst with high resistance to sulfur for hot gas cleaning at low temperature by partial oxidation of tar derived from biomass
Introduction
Environmentally friendly and more efficient ways to produce energy are very important subject for the reduction of CO2 emission. It is thought that biomass has the highest potential on a worldwide scale among the renewable energy sources [1]. Recently, catalytic hydrogen production from the biomass-derived materials has been reported [2], [3], [4]. Gasification of biomass to produce the gaseous fuels for gas turbines and gas engines has also attracted significant interest. However, the cleaning of produced gas is the bottleneck in the gas utilization [5]. The continual build-up of condensable organic compounds (named as tars) present in the produced gas can cause the blockage and corrosion, and also reduce overall efficiency [6]. Researches on Ni catalysts for hot gas cleaning by tar removal have been carried out at high temperature (1073–1173 K), and it has been reported that the product gas in biomass gasification contains minor impurities like sulfur compounds (H2S, COS) and this can deactivate Ni catalysts during the operation [7], [8], [9], [10]. Recently, we have reported that novel Rh/CeO2/SiO2 catalyst was very effective in the gasification of cellulose used as a model compound of biomass [11], [12], and that Rh/CeO2/SiO2 exhibited much higher and more stable activity in wood biomass (cedar) than the conventional gasification methods such as Ni catalysts, dolomite, and non-catalyst [13], [14], [15], [16]. In this communication, we found that Rh/CeO2/SiO2 exhibited much higher performance in the partial oxidation of tar from the biomass pyrolysis under the presence of H2S at low temperature such as 823 K than a commercial steam reforming Ni catalyst and non-catalyst.
Section snippets
Experimental
The CeO2/SiO2 support was prepared using granule SiO2 (CARiACT G-6, size 0.18–0.50 mm, BET = 535 m2/g) supplied from Fuji Silysia Chemical Ltd. The CeO2/SiO2 was prepared by the incipient wetness method using the aqueous solution of Ce(NH4)2(NO3)6. The loading of CeO2 on SiO2 was in the range of 30 mass%. After loading the Ce salt on SiO2, it was dried at 383 K for 12 h following the calcination at 773 K for 3 h under air atmosphere. Then the Rh was loaded on CeO2/SiO2 by impregnation of the
Results and discussion
Fig. 2 shows the catalytic performance as a function of time on stream in POT derived from the pyrolysis of cedar wood under the presence of 168 ppm H2S. The formation rate of H2 and CO clearly decreased with time on stream over the Ni catalyst. This profile indicates the gradual deactivation due to adsorption of sulfur. In contrast, the formation rate over Rh/CeO2/SiO2 was much higher and more stable than Ni catalyst. This result indicates that Rh/CeO2/SiO2 exhibits very high resistance to the
Conclusions
In the conversion of tar derived from the pyrolysis of biomass using catalysts, the effect of sulfur must be considered since biomasses can contain more or less sulfur component. In the catalytic partial oxidation of tar derived from cedar wood pyrolysis, Rh/CeO2/SiO2 catalyst exhibited much higher activity than the commercial steam reforming Ni catalyst. The Ni catalyst was deactivated drastically by the addition of H2S to the introduced gas and the performance was almost the same as that of
Acknowledgements
This research was supported by the Future Program of Japan Society for the Promotion of Sciences under the Project “Synthesis of Ecological High Quality of Transportation Fuels” (JSPS-RFTF98P01001) and the 21st Century COE program under the Ministry of Education, Culture, Sports, Science and Technology.
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