Study On Modified Ni/Cr-Mn-O And W-Ni-O Catalysts For Catalytic Activity Via Auto-thermal Reforming Of Acetic Acid

Issues of global warming and fossil fuels depletion have led to innovative technologies for producing clean energy.Hydrogen is widely considered as a clean energy carrier.The renewable resources for hydrogen production includes biomass,which is a renewable and carbon neutral clean resource.Ni-based catalysts showed high initial activity in the catalytic hydrogen production reaction,but deactivation by oxidation,sintering and carbon deposition is still an issue.Acetic acid in aqueous phase of bio-oilwas selected as model compound for the auto-thermal reforming of acetic acid to produce hydrogen.In the current work,Ni-based catalysts with different structures were prepared and tested for hydrogen production.The catalyst structure and acetic acid reaction mechanism were thoroughly explored through a series of characterization methods.Mn?II?Cr?III?O_x composites-supported Ni-based catalysts(Ni/Mn?II?Cr?III?O_x±?)were prepared via co-precipitation method,and tested in auto-thermal reforming?ATR?of acetic acid for hydrogen production in a fixed-bed reactor.Different process parameters,including reaction temperatures,O₂/HAc molar ratios and gas hourly space velocity?GHSV?,were studied in both static and dynamic conditions.The NM3C catalyst(Ni Mn_3.84Cr_1.61O_8.53±?)exhibited excellent catalytic activity and stability in a50-h ATR test:the HAc conversion reached 100%,and the hydrogen yield remained stable near 3.0 mol-H₂/mol-HAc with a rate of 367.4 mmol-H₂/(h·g_cat);meanwhile,the reactivity maintained stable with GHSV up to 45000 ml/?g·h?in both static and stop-restart test,in which neither carbon deposition nor sintering was found,showing potential for hydrogen production in on-board application.This improved reactivity can be due to 1)composites of spinel AB₂O₄phase?A=Mn?II?,B=Mn?III?or Cr?III??after calcination,2)stable Mn?II?Cr?III?O_x composites in which Mn O existed as skeleton with highly dispersed Cr species after reduction,3)high specific surface area with multi-layered structures,4)non-stoichiometric ratio of Mn?II?Cr?III?O_xspecies,which favors the transfer of electrons.Nano-SiO₂ support was prepared by a microemulsion method,and then a series of W-Ni/SiO₂ catalysts were prepared by the impregnation method for ATR of acetic acid for hydrogen production.The characterization results show that the 2W-Ni catalyst formed the Ni WO₄ phase after calcined.The active component of Ni highly dispersed on WO₄ skeleton after hydrogen reduction activation;The strong interaction between Ni and W restricts the migration and sintering of the active metal Ni at high temperature,which could improve the anti-sintering ability of the catalyst.At the same time,the electron transfer between multiple species of W(W⁴⁺-W⁵⁺-W⁶⁺)promotes the electron transfer in the catalytic reaction;In addition,the Nano-SiO₂ support provides a porous structure,which increases the surface area and facilitates the diffusion of the reaction gas in the catalyst,improving the catalytic performance of the catalyst.Therefore,the2W-Ni catalyst showed high catalytic activity and stability in the auto-thermal reforming of acetic acid for hydrogen production:The conversion rate of acetic acid was nearly 100%,and the hydrogen yield was stable at 2.9 mol-H₂/mol-HAc.After the reaction,no obvious sintering and carbon deposit was observed.