Synthesis, Characterization And Catalytic Performance In Dimethyl1,4-cyclohexane Dicarboxylate Catalytic Hydrogenation Of Highly Dispersed Copper-based Catalyst

1,4-cyclohexane dimethanol （CHDM）, which is one of the mostimportant chemical intermediates, has been preferred over ethylene glycol as astepping stone in the production of polyester fibers having excellent thermalresistance, transparency, and physical strength. To date, on an industrial scale,the only reported feasible route to CHDM is the catalytic hydrogenation ofdimethyl1,4-cyclohexane dicarboxylate （DMCD） by using Cr2O3promotedcopper-based heterogeneous catalysts. The toxicity of such type ofCr-containing catalysts, however, can cause a severe environmental pollution,and thus limits their practical applications, in addition to the high yield ofdesired product. Therefore, it has always been a challenge or a hot issue todevelop Cr-free catalysts with high activity and selectivity in thehydrogenation of DMCD. In addition, the Cu-based catalysts have been ofgreat interest due to their good activities and selectivities in a wide range ofreactions of various organic compounds. The most widely used preparation techniques for supported Cu^-based catalysts are deposition-precipitation andincipient wetness impregnation, which easily lead to the formation of copperparticles with large diameters and low metal loading amounts. In additional,the copper particle is easily sintered to large copper size during long termreaction, which inevitably leads to deactivation of copper-based catalyst.Therefore, different promoters and layered double hydroxides precursorare used to obtain highly dispersed copper-based catalyst, which exhibitexcellent performance in the catalytic hydrogenation of DMCD. Through aseries characterization, the relationship between the structure and catalyticperformance has been disclosed.（1） The gas-phase hydrogenation of DMCD to CHDM was conducted onwell-dispersed supported Cu/ZnO/ZrO₂catalysts. The results indicated that thestructure and catalytic performance of resulting copper-based catalysts wereprofoundly affected by the addition of zirconium. Moreover, theas-synthesized catalyst with35.0wt.%ZrO₂component was found to exhibitsuperior catalytic performance with a high CHDM yield of96.8%to othercatalysts, which should be mainly attributed to the significant dispersion effectof ZrO₂on the copper-containing species resulting in the higher metalliccopper surface area as well as the larger number of Cu⁺species.（2） Copper-based catalysts for gas-phase hydrogenation of DMCD toCHDM were prepared from a single-source Cu-Zn-Al layered doublehydroxide （LDH） precursor. The materials were characterized by powder X-ray diffraction （XRD）, thermogravimetry analysis coupled with massspectrometry （TG-MS）, temperature programmed reduction （TPR）, scanningelectron microscopy （SEM）, transmission electron microscopy （TEM）, andX-ray photoelectron spectroscopy （XPS）. The results revealed that thecomposition, texture, and structure of copper-based catalysts weresignificantly affected by the calcination temperature for LDH precursor.Moreover, the as-synthesized catalyst calcined at600°C was found to exhibitsuperior catalytic hydrogenation performance with the high CHDM yield of95.6%to the catalysts calcined at other temperatures and the traditional one,which should be attributed to the presence of the highly-dispersed activemetallic copper species, as well as reasonable surface chemical state overmetal oxide-based matrix thus facilitating the activation of ester groups ofreactants.（3） Lewis base promoted copper-based catalysts for gas-phasehydrogenation of DMCD to CHDM were prepared from Cu-Mg-Al layereddouble hydroxide （LDH） precursor with different Cu/Mg ratios. The materialswere characterized by XRD, TPR, SEM, TEM and CO^2-TPD. The resultsrevealed that the structure, dispersion and surface base property ofcopper-based catalysts were significantly affected by the addition ofmagnesium. Moreover, the as-synthesized catalyst with Cu^:Mg:Al=6:6:6achieved a lasting100%conversion with99.8%selectivity up to200hours.The unprecedented catalytic performance is ascribed to the synergistic effect between surface active Cu⁰sites and Lewis base sites.