Effect Of Activated Carbon Pore Structure On HI Catalytic Decomposition

Thermochemical sulfur-iodine cycle hydrogen production is currently a hot spot in the field of hydrogen energy preparation.The generation of H2 in the sulfur-iodine cycle is dependent on the decomposition of HI,and the decomposition of HI requires the action of a catalyst.Supported metal catalysts are widely studied,but there are problems such as easy deactivation,high cost and complicated process.Activated carbon,as a cheap and readily available catalyst material,has gradually attracted researchers' attention.The performance of activated carbon plays a key role in the catalytic decomposition of HI.Previous studies have screened coconut shell activated carbon with excellent catalytic performance,but the effect of preparation conditions on its physical properties and catalytic performance lacks systematic research.The change of the preparation conditions of activated carbon is the premise of pore structure regulation.This article creatively proposes the use of different preparation methods to directionally regulate the pore structure of activated carbon.The conventional carbonization method is used to prepare activated carbon mainly with micropores;the hydrothermal carbonization method is used to prepare graded pore activated carbon with similar proportions of micropores,mesoporous and macropores;and the CaCl2 impregnated hydrothermal carbonization precursor is used to prepare activated carbon mainly with mesoporous and macropores.At the same time,a small fixed-bed experimental platform was built to study the characteristics of HI decomposition catalyzed by activated carbon prepared under different conditions.The conventional carbonization method is used to produce coconut shell carbon.It is found that after conventional carbonization at 400?,600? and 800?,600?is found to be the optimal carbonization temperature,which is conducive to the further development of pore structure and catalyzes HI decomposition.For conventional carbonized precursors,the physical activation method is conducive to the development of activated carbon pore structure and catalyzes HI decomposition;the steam activation method is the best,followed by the CO2 activation method.The activation of KOH hinders the further expansion of the coconut shell carbon pore structure,and the catalytic effect is the worst.According to BET analysis,the higher the the specific surface area in the microporous coconut shell carbon,the higher the efficiency of its catalytic HI decomposition.For conventional carbonized precursors,within a certain range,increasing the activation time,the efficiency of coconut shell carbon catalyzing the decomposition of HI increases,but the effect of increasing activation time on the catalytic decomposition efficiency of HI is not obvious.The use of hydrothermal carbonization method to produce coconut shell carbon found that:when using hydrothermal carbonization method,increase the carbonization temperature,the proportion of mesoporous and macropores in coconut shell carbon gradually increases,the efficiency of catalytic HI decomposition gradually increases,240? is the optimal carbonization temperature.Activation can increase the content of C in coconut shell carbon.Compared with KOH activation,the closer the proportion of mesoporous and macropores in coconut shell carbon activated by steam and CO2 is to 50%,the better the effect of catalyzing HI decomposition.For hydrothermal carbonization precursors,when the activation temperature gradually increases,the efficiency of catalytic HI decomposition increases first and then decreases.800? is the optimal activation temperature.At this time,the closer the ratio of activated carbon micropores to mesoporous and macropores,and the pore structure is evenly distributed,and its catalytic effect on HI decomposition is the best.While increasing the activation time,the efficiency of coconut shell carbon to catalyze the decomposition of HI gradually increases.Combined with BET characterization,it can be found that in the graded pore activated carbon,when the proportion of mesoporous and macropores exceeds 50%,the effect of activated carbon on HI decomposition is inversely proportional to the ratio of mesoporous and macropores.After impregnating the hydrothermal carbonization precursor with CaCl2 solution,it is found that the proportion of mesopores and macroporous in the coconut shell carbon obtained by impregnation of the CaCl2 solution increases,but it is not conducive to its catalytic HI decomposition.After the proportion of mesopores and macropores exceeds 50%,the higher the proportion of mesopores and macroporous,the lower the efficiency of its catalytic HI decomposition.Therefore,in the catalytic decomposition reaction of HI,the catalytic activity of activated carbon is the result of the synergistic effect of micropores,mesopores and macroporous.The graded pore activated carbon is most beneficial to catalyze the decomposition of HI.As for the coconut shell carbon of the same type of pore structure,the larger the specific surface area,the better the catalytic effect of HI decomposition.