Study On The Effects Of Activated Carbon Functional Groups On HI Catalytic Decomposition

With the depletion of traditional energy and the serious environmental problems caused by it,it is urgent to develop new energy.As a kind of clean energy with zero pollution,hydrogen energy has rich sources,high energy density and wide application,and has become the best choice to replace traditional energy sources such as fossil fuels.Among many hydrogen production methods,the thermochemical sulfur-iodine(SI or IS)cycle has been widely concerned because of its advantages of low cost,environmental protection and large-scale application.The decomposition of hydrogen iodide(HI)is the step of hydrogen generation in the whole cycle,and its related catalyst research is a hot topic to improve the rate of hydrogen production.Research shows that activated carbon materials such as activated carbon are cheap,easily available and efficient.It can make the HI conversion close to its equilibrium conversion(23%)at 500?,and is suitable for large-scale industrial application.In the activated carbon study,researchers have pointed out the influence of the ash content,specific surface area and pore volume on HI decomposition including preparation and treatment process.However,as an important chemical property of activated carbon,the effect of functional groups on the catalytic decomposition of HI by activated carbon has not been unanimously determined.In this paper,the contents of nitrogen and oxygen in activated carbon were controlled through N-doping and reduction modification,exploring the influence of functional groups of O-containing and N-containing on catalytic decomposition of HI.In addition,we combined with quantum chemistry calculation methods to verify the experimental results and reveal the experimental mechanism-This paper can provide underlying guidance for preparing highly efficient activated carbon for HI decomposition.In this paper,a series of N-doped activated carbon were prepared from coconut shells by adding urea during hydrothermal carbonization and the subsequent CO2 activation.The characterization experiment and the activity evaluation of HI decomposition were conducted to study the effect of N-containing functional groups on the catalytic decomposition of activated carbon HI.The results showed that the addition of urea during the hydrothermal carbonization aided in the successful doping of N-containing functional groups contained pyridinic N(N-6),pyrrolic N(N-5),and quaternary N(N-Q)into the carbon structure.And pyrrole N(N-5)accounted for the largest proportion.After doping,the N contents of the sample increased from 0.19%to 6.27%,and the HI conversion increased from 12.38%to 22.84%,indicating the two parameters were positively closely related to a large extent.Meanwhile,N-doping lead to decreases in oxygen content,specific surface and pore capacity.However,the deoxygenation experiment and related literatures excluded the influence of factors of oxygen and pore structure on HI decomposition in the paper.Therefore,N-containing functional groups are beneficial to the catalytic decomposition of HI over activated carbon materials.In this paper,quantum chemistry method is used to calculate HI chemisorption and H2 chemical desorption after N-doping.Results showed that N-containing functional groups are not active sites for HI decomposition over activated carbon,but can change their physical adsorption.N-containing functional groups have opposite effects on HI chemisorption and H2 chemical desorption on unsaturated carbon atoms.On the whole,N-5 is to promote HI decomposition over activated carbon;N-6 and N-Q showed inhibition of it.Above experimental results were derived from the promotion of N-5.Relative contents of N-5 should be increased in the directional regulation of N-doped activated carbon for HI decomposition.In this paper,KGE activated carbon was reduced by hydrogen at different temperatures.The characterization experiment and the activity evaluation of HI decomposition were conducted to study the effect of O-containing functional groups on HI decomposition over activated carbon.The O contents were controlled between 4.35%and 10.68%,the specific surface area was about 1000m2/g,and the pore volume was about 0.45cm3/g.After the reduction of O-containing functional groups,HI conversion was increased from 12.38%to 22.84%.It can be independently determined that O-containing functional groups can inhibit HI decomposition over activated carbon.In this paper,HI chemisorption and H2 chemical desorption before and after the reduction were calculated by quantum chemistry method.Results showed that O-containing functional groups are not active sites for the HI decomposition over activated carbon,but can change their physical adsorption,O-containing functional groups can promote or inhibit HI chemisorption and H2 chemical desorption to varying degrees.On the whole,O-containing functional groups not conducive to HI decomposition over activated carbon,which is consistent with the experimental results.Therefore,the relative contents of O-containing functional groups should be reduced in the directional regulation of activated carbon for HI decomposition.