CoMn-Based Catalyst Design And Study On The Transfer Hydrogenation Of Levulinic Acid To γ-Valerolactone

Aqueous-phase hydrodeoxygenation of biomass derived feedstocks to renewable chemicals and fuels is important for sustainable development of chemical industry.It is well known that,traditional hydrogenation processes using molecular H₂ are usually conducted under harsh temperatures（>150℃）or pressures（>3 MPa）,which are usually not friendly to catalysts and cause huge emission of greenhouse gases such as CO₂ and methane.It can not be ignored that the use of H₂,still derived from fossil fuels,makes biomass conversion costly and unsustainable.In contrast,catalytic transfer hydrogenation（CTH）in the absence of externally added H₂ display both technological and economic advantages,since the reaction is conducted under milder conditions with inexpensive liquid donors（alcohols,acids and hydrazine）which result in safe reaction environment,efficient atomic economy and low-cost capital investment.Levulinic acid（LA）is a promising biomass platform molecule produced from the hydrolysis of cellulose under acidic conditions.It exhibits great potential as an excellent platform molecule for the production of various downstream chemicals,which involves hydrogenation of LA toγ-valerolactone（GVL）as the key conversion step.CTH of LA using H-donors represents one of the most promising routes compared to conventional hydrogenation processes using fossil-derived H₂.It is known that the effect of metal composition and metal-support interaction on tandem H₂ generation and hydrogenation have been extensively studied on catalyst design.However,the influence of lattice distortion on catalytic C-H and C=O bond cleavage have not yet been reported in the literature.In this work,we proposed unique CoMn oxide catalysts for conversion of LA to GVL using formic acid（FA）as H-donor.The key finding is that,lattice distortion of CoMn oxides induces electronically coupled CoMn O₃ phase at Co Ox-Mn Ox interface leading to catalytic performance enhancement.Catalyst characterization by BET,XRD,XPS,and TEM techniques further demonstrate the synergism at Co Ox-Mn Ox interface for tandem hydrogenation reactions.Kinetic analysis confirms an induction period of LA conversion.There exists competitive reactions between LA activation and FA decomposition on catalyst surface.H species accumulated on CoMn catalyst surface are activated first and then react with LA to generate GVL without external H₂ in aqueous medium.We proposed two plausible reaction mechanisms as follows.（Ⅰ）In the early stage of the reaction（e.g.,before 4 h）,H₂ is released from the decomposition of FA and adsorbed on the surface of catalyst to undergo activation stage.Subsequently,the H₂species generated in-situ activate ketone group in LA molecules.Thus conversion of LA to GVL can be facilitated after 4 h.（Ⅱ）As another possible pathway,FA competitively occupy the adsorption site of LA on catalyst surface and decompose to release H₂.LA have access to active sites only when decomposition of FA is completed.Therefore,induction period is observed for LA conversion.In summary,we first proposed CoMn oxide catalysts for CTH of LA to GVL using FA as H-donor,which show enhanced stability and activity（80%LA conversion and 80%GVL selectivity,reused at least 5 times）due to lattice distortion caused by strong Mn-Co interaction in CoMn O₃ phase.And kinetic analysis indicated the present of induction period on catalyst surface.