Product-targeted Hydrogenation Of Dimethyl Oxalate:Ni-foam Structured Ni-based Alloy Catalysts And Alloy Catalysis

As the demand for oil-related derivatives boomed and the shortage of crude oil resources became increasingly severe in the past decades,to pave the way for efficient and eco-friendly utilization of the diverse non-oil resources?such as coal,natural gas,renewable biomass,and even organic wastes?with the aid of effective catalytic processes to produce highly value-added fuels and community chemicals has turned out to be a hot spot in scientific research and modern industries.The persevering researches on syngas conversion can bridge the gap between the non-oil resources and the chemicals-fuels production because syngas can not only be costly produced from the above-mentioned non-oil resources but also be versatilely used as basic blocks to produce fuel and chemicals.For instance,gas-phase hydrogenation of syngas-derived dimethyl oxalate?DMO?is an attractive alternative for the synthesis of methyl glycolate?MG?,ethylene glycol?EG?and ethanol?EtOH?synthesis.Although the industrial demonstration of DMO hydrogenation has been successfully realized in China,the Cu/SiO₂ catalyst still faces some inherent problems,such as the severe agglomeration of Cu nanoparticles,the dissolution erosion of SiO₂ and a narrow temperature window with high selectivity of single target product.Moreover,the local overheating owing to the exothermic DMO hydrogenation process and poor thermal conductivity of SiO₂easily brings hotspots in catalyst bed and further expedites the above problems.Aiming at this situation,a series of promising Ni-foam-structured Ni-based alloy catalysts engineered from nano-to macro-scales with excellent combination of outstanding heat/mass transfer ability,high porosity,and high catalytic performance is developed for the DMO hydrogenation process,according to the“Top-Down”preparation strategy.The main contents of this thesis are summarized as follows.?1?Ni₃P nano-alloy structured on a Ni-foam as superior catalyst for hydrogenation of dimethyl oxalate to methyl glycolateMethyl glycolate is a versatile chemical widely used as drug carrier,medical suture and biodegradable plastics,and it can be massively produced via the DMO hydrogenation,but the qualified catalyst with high MG selectivity is still a grand challenge under complete DMO conversion.Herein,we describe the discovery of a high-performance Ni-foam-structured Ni₃P nano-alloy catalyst?8.0 mm diameter;1.5mm thick;100 pores per inch?for the DMO-to-MG reaction.Initially,the nanoporous Ni₂P was endogenously grown onto the Ni-foam substrate but the as-obtained Ni₂P/Ni-foam catalyst did not yield satisfying activity and selectivity for the titled reaction yet.Interestingly,exclusive transformation of Ni₂P into Ni₃P took place with well-preserved nanoporous structure during the reaction.The as-formed Ni₃P/Ni-foam catalyst delivers an almost full DMO conversion with 95%-97%MG selectivity within 1000 h at 230^oC,and particularly,maintains 92-97%MG selectivity in a wide range of reaction conditions.Obviously,such catalyst achieves the facile control of high MG selectivity in the multistep DMO selective hydrogenation reaction.As revealed by CO-uptake,the number of active sites in the Ni₃P/Ni-foam catalyst is 1.7 time that of the Ni₂P/Ni-foam,which ensures the high DMO conversion.Kinetic experiments and DFT calculations show that,compared with Ni₂P,MG is more inclined to molecular adsorption rather than dissociative adsorption?the starting point for the following hydrogenation?on Ni₃P,and Ni₃P offers quite higher activation energy for MG over-hydrogenation to EG,thereby markedly improving the MG selectivity.?2?Nano-intermetallic InNi₃C_0.5 structured on a Ni-foam as superior catalyst for hydrogenation of dimethyl oxalate to ethylene glycolEthylene glycol is widely used in industry as the key organic compound,and its massive production via gas-phase hydrogenation of DMO is an attractive alternative to oil-based route,but the insufficient catalytic stability of Cu-based catalysts and the narrow temperature window with high EG selectivity are still significant bottlenecks for their industrial applications.Herein,we report the discovery of a Ni-foam structured InNi₃C_0.5 catalyst that is capable of fully converting DMO with 96%under industrial-relative reaction conditions,and particularly is stable for at least 2500 h without any sign of deactivation.More encouragingly,such catalyst shows a wide operating temperature window?200-250 ^oC?for high EG selectivity?above 90%?,which is significantly important in industry due to the local overheating in catalyst bed.As revealed by kinetic experiments and theoretical calculations,the EG formation is easy to occur but its over-hydrogenation to EtOH is hindered by the high reaction barrier thereby achieving the facile control of a high intermediate EG selectivity in the multistep DMO hydrogenation reactions even at high temperature.Moreover,the InNi₃C_0.5/Ni-foam can be extended to a broad scope of carbonyl compounds hydrogenation with high yields of corresponding alcohols.?3?FeNi₃-FeO_x nanocomposite structured on a Ni-foam as superior catalyst for hydrogenation of dimethyl oxalate to ethanolEthanol synthesis from DMO hydrogenation is of crucial significance for environment-and energy-related applications,but the high-performance catalysts represent the grand challenge.Herein,a low-temperature highly active,selective and stable Ni-foam-structured FeNi₃-FeO_x nanocomposites catalyst is developed for this reaction.Such catalyst was tailored as follows:the hydrothermally-synthesized Ni?OH?₂/Ni-foam was initially impregnated with aqueous solution of iron?III?nitrate;the as-obtained sample was then calcined preferably at 550 ^oC?to adequately form NiFe₂O₄-NiO composites?followed by H₂-reduction at 350 ^oC?to transform NiFe₂O₄-NiO into FeNi₃-FeO_x?to obtain the preferred FeNi₃-FeO_x/Ni-foam-?550/350?catalyst that achieves a turnover frequency of 88.8 h^-1 at 180 ^oC.This catalyst delivers a full DMO conversion with 98%EtOH selectivity at 230 ^oC,2.5 MPa,using a H₂/DMO molar ratio of 90 and a WHSV_DMO of 0.44 h^-1,and particularly,being stable for at least700 h.The H₂/DMO molar ratio and reaction temperature are much lower than those?150 and at least 270 ^oC?for the Cu-based catalyst.As revealed by the control experiments,EtOH is formed dominantly through the hydrogenation of EG instead of methyl acetate.In nature,the NiFe₂O₄-NiO derivation strategy endues our catalyst with abundant interface between FeNi₃ nanoalloy and FeO_x fragments?acting as acid sites?,promoting the activation of ester and hydroxyl groups,thereby markedly enhancing the EtOH yield.Moreover,other“alloy-oxide”catalysts are also capable of converting DMO into EtOH.For instance,the MoNi₄-MoO_x/Ni-foam catalyst tailored through a NiMoO₄ derivation strategy,achieves 93%EtOH yield under relatively mild conditions.