Non-noble, efficient catalyst of unsupported α-Cr 2 O 3 nanoparticles for low temperature CO Oxidation (original) (raw)
Herein, we report the synthesis of chromium oxide nanoparticles, α-Cr 2 O 3 NPs, followed by full characterization via XRD, SEM, XPS, and N 2 sorptiometry. The synthesized nanoparticles were tested as catalysts toward the oxidation of CO. The impact of calcination temperature on the catalytic activity was also investigated. CO conversion (%), light-off temperature, T 50 , data were determined. The results revealed that chromia obtained at low calcination temperature (400 °C) is more active than those obtained at high calcination temperatures (600° or 800 °C) and this is ascribed to the smaller particle size and higher surface area of this sample. The results revealed a superior catalytic activity of Cr 2 O 3 NPs at lower temperature as we reached a complete conversion at 200 °C which is high value in the forefront of the published results of other non-noble catalysts. The high activity of Cr 2 O 3 nanoparticles (T 50 as low as 98 °C) where found to be dependent on a careful selection of the calcination temperature. These results may provide effective and economic solutions to overcome one of the major environmental threats. The primary pollutants from vehicles comprised of carbon monoxide (CO), hydrocarbons (HCs) and nitrogen oxides (NOx) 1. These three harmful pollutants are major source of air pollution and it affects humans, vegetation, and atmosphere in number of ways. Among all types of exhaust gases carbon monoxide is most harmful 2. Carbon monoxide is an odourless, colourless and toxic gas. It is also called the silent killer and its known to contributes indirectly to global warming and ozone depletion 3. Thus, CO levels in the ambient air play a role in determining the air quality of a region. Noble metals are known for their high oxidation power and terms as paramount in automobile industry since the seventeenth century. So far, most of effective catalysts for this system have been reported to use the supported noble metals 4-9. These catalysts exhibited high activities for CO oxidation; however, they have some disadvantages with a high cost, a limited availability and low selectivity at high temperatures. Although not as efficient as noble catalysts, some non-noble metal oxides (e.g. CeO 2-based catalyst) show high activity for CO oxidation, and hence, still advantageous due to their lower cost. For example, the light-off temperature, T 50 , for a CoOx/CeO 2 catalyst was reported to be 135 °C (i.e. 50% of CO converted to CO 2 at that temperature) 10. Reported also CuO-CeO x hybrid ceria catalyst for CO oxidation and showed T 50 around 94 °C 11. Also, Fe-Cu/CeO 2 composite catalysts were tested for CO oxidation and showed T 50 around 158 °C 12. Also, Co 3 O 4 @ CeO 2 core shell cubes with optimized CeO 2 shell thickness exhibited 100% conversion of CO at 190 °C in CO oxidation 13. Recently, CO oxidation at low temperature with nonprecious metal based catalysts was an important research goal 14-18. With a special focus to Cr 2 O 3 , very rare reports disclosed its usage for CO oxidation. Ghandhi et al. 19 reported the CO oxidation using Cr 2 O 3 and they obtained T 50 values of 265 °C. Ren et al. 20 reported the T 50 values of 200 °C-pretreated mesoporous Cr 2 O 3 at 151 °C and they found it to be higher than those of the corresponding 400 °C-pretreated Cr 2 O 3 which was 147 °C. The present work aimed to produce a non-noble metal catalyst (other than the extensively studied cerium oxide catalyst) with a high activity for the CO catalytic oxidation at lower temperature. Based on a literature survey, it is the first time to utilize nano chromia as a catalyst, without doping it with other metal oxide or using a support, for CO oxidation with such low-temperature efficiency. In this context, we prepared chromia nanoparticles via simple method at different calcination temperatures. Full characterization to the synthesized nanoparticles was investigated to stand on the most promising characteristics leading to efficient catalytic activity.