Study On The Structural Regulation Of Ni-CaO-based Bifunctional Catalysts And Their Enhanced Hydrogen Production Performance By Biogas Adsorptio

Biogas is a renewable carbon neutral energy with a wide range of sources and extremely rich production.Biogas contains a large amount of methane,which is very suitable for use as biofuel.Bio-methane with high calorific value obtained through the biogas upgrading process is widely used in CHP（Combined Heat and Power）and gas fields,but this process is complicated.The decarbonization process is costly and also faces the problem of the separation and treatment for the large amount of CO₂.Hydrogen production from biogas can reduce the emission of two greenhouse gases,CH₄ and CO₂,and alleviate the dependence of hydrogen production on fossil fuels.On the other hand,the cost of biogas reforming for hydrogen production is relatively low,which giving it obvious economic advantages in many hydrogen production technologies using renewable energy.Biogas Sorption Enhanced Reforming（SESRB）reaction is an ideal method to produce hydrogen from biogas.It can obtain high-purity hydrogen from biogas in one step,thus avoiding excessive separation operations.At the same time,the in-situ capture of CO₂ effectively solves the key problem facing biogas hydrogen production-high CO₂ content,and has good adaptability to biogas from different sources.In the SESRB process,there are issues with low efficiency and uneven mixing when using physical mixing of catalysts and adsorbents.Bi-functional catalysts that integrate catalytic and sorption properties into one particle provide a better choice.However,bi-functional catalysts have a low specific surface area and are often non-porous or poorly porous,leading to sintering issues.This paper first achieved long-term stability in the SESRB reaction by reasonably designing and regulating the structure of the Ni-Ca O based bi-functional catalysts.A Ni-Ca O-Mg O bi-functional catalyst with a hollow porous microsphere structure and uniform distribution of components was synthesized using an alkali-modified carbon sphere template method.The alkali-modified carbon sphere method increased the yield of the bi-functional catalyst by 14 times,effectively solving the problem of low yield when preparing catalysts using the traditional template method.This was related to the increase in surface alkalinity and oxygen containing functional groups of carbon spheres by alkali modification treatment,thereby improving their adsorption ability for metal ions.In the evaluation of CO₂ sorption-desorption performance and SESRB performance,the rich porous structure and uniformly dispersed particles in the 1Ni-Ca Mg6-M bi-functional catalyst played a key role in inhibiting the sintering of Ca species,ensuring the high stability of cyclic operation.After 15 cycles of repeated CO₂ sorption-desorption,1Ni-Ca Mg6-M still maintained 62%of its initial sorption capacity.The purity of H₂ remained above 92.3 vol%during the pre-breakthrough stage for the entire 10 cycles of SESRB reaction.The porous Ni-Pb O-Ca O bi-functional catalyst was prepared by combining the template and inert component.It utilized the adsorption between Ca CO₃ and Pb²⁺to uniformly introduce a layer of high-temperature inert material（Ca Pb O₃）on the Ca O surface of the bi-functional catalyst.It could achieve a balance between the preservation of the porous structure and the uniform introduction of a small amount of inert components.The prepared 2Ni-8Pb O-Ca O bi-functional catalyst had a fluffy and porous structure,and the inert component（Ca Pb O₃）was uniformly distributed in the 2Ni-Ca O bi-functional catalyst.The bi-functional catalysts containing Ca Pb O₃ all showed high stability in the performance of CO₂ sorption-desorption test.When the pore structure properties of the bi-functional catalysts were similar,the higher the Ca Pb O₃ content,the more obvious the improvement effect on the stability of bi-functional catalysts.This was related to the effective separation of Ca O and Ni particles by Ca Pb O₃,which inhibited the sintering of Ca species and thus ensured the cycle stability.As an optimized bi-functional catalyst,2Ni-8Pb O-Ca O showed only a 40%decrease in sorption enhancement effect throughout the entire 20 cycles of SESRB reaction,and the H₂ purity remained at 94.1vol%in the pre-breakthrough stage.This work has guiding significance for the production of high-purity hydrogen from biogas without emitting CO₂,and also provides a new idea on how to improve the stability of Ni-Ca O based bi-functional catalysts.