Fabrication Of Copper-based Catalysts Based On Hydrotalcite Composites And Study On The Catalytic Reaction Performance Of CO₂ Hydrogenation

The excessive use of fossil fuels not only causes energy crisis,but also a series of environmental problems such as global warming and ozone depletion caused by a large number of CO₂ emissions,which seriously endangers human health and safety.CO₂ hydrogenation and reduction is an important means to alleviate the above problems.It can also generate important chemicals such as methane?CH₄?,carbon monoxide?CO?,methanol?CH₃OH?and formic acid?HCOOH?while consuming CO₂,which is helpful to alleviate the practical problem of fossil energy depletion and is of great significance for resource recycling and environmental protection.However,due to the chemical inertness of CO₂and the limitation of reaction kinetics,the research and development of high-performance catalyst is the premise of CO₂ hydrogenation reduction.At present,Cu-based catalysts have been widely studied because of their advantages such as low price,large specific surface area and good dispersion.However,the active components on the catalyst surface are easy to agglomerate,and the presence of reverse water gas reaction makes the product methanol selectivity low.In order to solve these problems,Cu-based catalyst based on hydrotalcite composite was constructed by nanotechnology in this paper.The main research contents are as follows:1.Hierarchical sheet-like Cu/Zn/Al nanocatalysts derived from layered double hydroxides?LDHs?and metal organic framework?MOF?nanoparticles as two solid precursors for CO₂ hydrogenationreduction.The uniform loading of Zn-BTC nanoparticles on Cu-Al LDH surface was achieved by an insitu growth method at mild conditions.It was found that the pretreatment of the LDH with acetone could effectively exfoliate the sheet-like structure,increase the specific surface area,and facilitate the immobilizationof Zn-BTC nanoparticles.Afteroptimizing the preparation conditions,Cu/Zn/Al nanocatalysts significantly improved the selectivity of methanol.It was found that both the existence of ZnO and the pretreatment of LDH with acetone significantly reduced CO selectivity by increasing the activation energy.Moreover,in-situ DRIFTS study indicates that the promoting effect of ZnO on methanol formation is mainly associated with the formation of a higher amount of ^*CH₃O intermediate rather than^*CO and ^*HCOO species on the catalyst surface.2.A range of molecular metalloporphyrins TCPP?M?were used as carriers to immobilize transition metals ions(e.g.,Zn²⁺,Co²⁺,Ni²⁺,and Fe²⁺)into the interlayer space of laminar Cu-Al layered double hydroxides?LDHs?.The obtained TCPP?M?@Cu-Al LDH were then used as solid precursors for the fabrication of a series of heterogeneous catalysts for CO₂hydrogenation via high-temperature calcination.Importantly,the deprotonated TCPP?M?not only provides nitrogen-based coordination sites to anchor a series of transition metal atoms but also intercalates into the interlayer gallery of LDHs by ion exchange.Both LDH confinement and TCPP complexation contributed to the enhanced dispersion of the active species over the catalyst surface structures.Remarkably,the transition metals positioned within the confined space of LDH significantly affected the catalytic performance of CO₂ hydrogenation,and the selectivities of which were highly dependent on the reaction intermediates as suggested by the in-situ DRIFTS study.Moreover,the designed catalysts fabricated via molecular TCPP?M?intercalation exhibited much better performance than the conventional catalysts derived from surface supported CA-LDH,due to the better metal dispersion and smaller particle size.