A novel robust hybrid metaheuristic optimization approach, which can be considered as an improvement of the recently developed bat algorithm, is proposed to solve global numerical optimization problems. The improvement includes the addition of pitch adjustment operation in HS serving as a mutation operator during the process of the bat updating with the aim of speeding up convergence, thus making the approach more feasible for a wider range of real-world applications. The detailed implementation procedure for this improved metaheuristic method is also described. Fourteen standard benchmark functions are applied to verify the effects of these improvements, and it is demonstrated that, in most situations, the performance of this hybrid metaheuristic method (HS/BA) is superior to, or at least highly competitive with, the standard BA and other population-based optimization methods, such as ACO, BA, BBO, DE, ES, GA, HS, PSO, and SGA. The effect of the HS/BA parameters is also analyzed.
Nanostructured Co 3 O 4 -CeO 2 and CuO-CeO 2 catalysts with the specific surface areas exceeding 100 m 2 g -1 were synthesized by a surfactant-templated method. The catalytic performance of these catalysts was investigated using the total oxidation of CO and C 3 H 8 as model reactions. The results show that the Co 3 O 4 -CeO 2 catalysts are less active for CO oxidation but are more active for C 3 H 8 oxidation as compared with the CuO-CeO 2 catalysts. Moreover, the Co 3 O 4 -CeO 2 catalysts exhibit a volcano-type performance for CO oxidation with the cobalt content increasing. The in situ diffuse reflectance infrared spectroscopy (DRIFTS) study shows that CO is adsorbed mainly as carbonyl (2106 cm -1 ) and bidentate carbonate (1568 and 1281 cm -1 ) on CuO-CeO 2 , and only as bidentate carbonate (1591 and 1268 cm -1 ) on Co 3 O 4 -CeO 2 . On the basis of the results of structural characterization, redox properties, and in situ DRIFTS study, the active sites for CO and C 3 H 8 oxidation are identified, respectively. Carbon monoxide oxidation preferentially occurs at the interface between CeO 2 and CuO or Co 3 O 4 , whereas propane oxidation takes place on the neighboring surface lattice oxygen sites in CuO or Co 3 O 4 crystallites. The different requirements of the active sites are determined by the different reaction mechanisms and the rate-determining steps. It is also found that the introduction of a small amount of Pd to Co 3 O 4 -CeO 2 can remarkably promote the CO oxidation activity, but it hardly enhanced the C 3 H 8 oxidation activity of the catalyst. The different reaction mechanisms, on molecular level, are identified and discussed in detail.
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