| Hydrogen,as a clean efficient and renewable energy,has received more attention for decades.In the current work,auto-thermal reforming?ATR?of acetic acid?HAc?was chosen as a feasible method for hydrogen production.Cobalt-based catalysts have been considered as a promising candidate for ATR of HAc and exhibited activity and selectivity in ATR.However,deactivation by cobalt metal oxidation,sintering and coking are still concerns for application.Therefore,to develop and design catalysts with high efficiency and stability,it is necessary to explore the reaction mechanism concerning structure of catalysts,the interaction between metal-support and Co particles size.Hydrotalcite-derived Co/Sr-Alx-O catalysts with different Sr/Al molar ratios?x=0,1/12,1/6,1/2,2?were prepared by coprecipitation,and tested in ATR of HAc for hydrogen production.Characterizations of XRD,H2-TPR,BET,XPS,TG-DSC and TEM were carried out.The characterization results indicated that the hydrotalcites[?CoSr?1-xAlx 3+?OH-?2]x+[(CO32-)x/n·yH2O]was obtained over the Co/Sr-Al1/6-O catalyst,in which the cobalt species were incorporated into the hydrotalcites and were stabilized in the layered-structured support during catalyst preparation.After thermal treatment?e.g.,calcination and reduction?,the Co metal was highly dispersed over the Sr?Al?O mixed oxide with strong interaction.Thus,the Co/Sr-Al1/6-O catalyst produced a high activity and enhanced stability:the conversion of HAc reached 100%and the H2 yield remained stable near 2.6 mol-H2/mol-HAc with turnover frequency?TOF?at 0.80 s-1.Meanwhile,no obvious coking was found over the Co/Sr-Al1/6-O catalyst,which was due to the highly dispersed cobalt particles over the Sr?Al?O support with strong interaction.Perovskite-like catalysts of Ti1-xSrxCoO3?x=0,0.2,0.33,0.5,0.67,0.8?were prepared by sol-gel method,and then tested in ATR of HAc for hydrogen production;Active species,structure of carriers and the relationship between structure and properties were studied as well.The results showed that the fine Co particles interacted with the perovskite-type oxides and partially incorporated into the perovskite structure,leading to formation of Ti1-x-x SrxCoO3.The perovskite structure favored to small Co particles and effectively prevented the agglomeration of Co particles,improving the stability of the catalyst.Meanwhile,the partial substitution of Ti by Sr resulted in more crystal defects in the perovskite oxides.Therefore,the perovskite-like catalyst of Sr-doped TSC0.5 showed optimized activity and enhanced stability:the conversion of HAc reached 100%and the H2 yield remained stable near 2.86 mol-H2/mol-HAc.Additionally,no obvious coking was found over the TSC0.5 catalyst,suggesting small Co particle size and its strong metal-support interaction could suppress formation of coking,and thus improve hydrogen selectivity. |
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