Preparation,Characterization And Performance Of Metal Fiber-/Foam-Structured Catalysts For Dimethyl Oxalate Hydrogenation And Fischer-tropsch Synthesis To Lower Olefins

Catalytic reaction essentially involves the surface/interface process,which is usually limited by the heat/mass transfer for the industrial scale-up,leading to the decline of catalytic performance.Structured catalyst is a hot intersectional topic between catalysis and chemical engineering due to the enhanced heat/mass transfer and improved hydrodynamics.The development and application of structured catalysts depend on coating technology,and structured ceramic honeycomb catalysts prepared by coating technology have realized large-scale industrial application in purifying automobile exhaust.Compared with structured ceramic supports,metal fiber/foam-based supports with the unique three-dimensional（3D）network structure own more advantages in intensifying heat transfer,eliminating diffusional limitation in radial direction,enhancing eddy-mixing mass transfer,large-scale preparation and so on.However,it is difficult to form a strongly adhesive coating by conventional washcoating technique for the large thermal expansion coefficient of metal,leading to the crack and exfoliation of coatings.Therefore,it is urgent to develop a novel strategy of catalytic functionalization for stuctured metal fiber/foam materials（non coating technology）."Rich coal,deficient oil,lean gas" is the characteristic of our country’s energy structure,and the engineering projects,such as "coal to ethylene glycol（EG）","coal to ehtanol" and"coal to lower olefins",gain supporting vigorously of our government.The key reactions involved in the above projects,such as dimethyl oxalate（DMO）hydrogenation to EG/ethanol and Fischer-Tropsch to lower olefins（FTO）,are all mass-transfer limited and strongly exothermic reactions.Based on the "Top-Down" design philosophy,namely reactor（Top,hydrodynamics and transfer）-catalyst（Down,surface/interface reaction）,we developed metal-fiber/foam-structured catalysts via novel galvanic deposition and in-situ hydrothermal growth method,using metal fiber felt/foam supports with the unique three-dimensional（3D）network structure,enhanced heat/mass transfer and improved hydrodynamics properties.These catalysts exhibited good catalytic activity/selectivity and stability for DMO hydrogenation to EG/ethanol and FTO reactions,which realized the collaborative coupling between reactor（hydrodynamics and transfer）and catalyst（surface/interface reaction）.The content and main results of this dissertation consisted of three parts as following:（1）Cu-fiber structured La₂O₃-PdAu（alloy）-Cu catalysts for dimethyl oxalate selectively hydrogenation to ethylene glycolOur previous work has demonstrated 0.1Pd-0.5Au-CuOx/Cu-fiber prepared by galvanic deposition method could deliver 93%EG yield at 270 ℃ and was stable for 200 h.However,this catalyst showed poor low-temperature activity.In this thesis,0.1Pd-0.5Au-CuOx/Cu-fiber was post-modified by 2 wt%La₂O₃ and consequently showed enhanced low-temperature activity and stability,delivering 93.4%EG yield and stable activity/selectivity for 500 h.H₂-TPR,NH3-TPD and XPS results illuminated the nature for enhanced low-temperature activity and stability associated with the La₂O₃:（1）Lewis acidity of La₂O₃ promoted H-spillover;（2）La₂O₃-assisted enhancement of the electron deficiency of the PdAu alloy facilitated H₂ activation;（3）Partially-reduced surface LaOx species were active for activating the ester groups of DMO;（4）La₂O₃ could stabilize the Cu’ species.（2）Metal-foam stuctured Fe based catalysts for dimethyl oxalate selectively hydrogenation to ethanolCupronickel-foam@Nanoporous Cu composite could be obtained by partially leaching surface Ni from cupronickel-foam pellets（80 wt%Cu-20 wt%Ni,2 mm in diameter）in hydrochloric acid（2 M）.The resulted composite was impregnated（incipient wetness）with ferric nitrate aqueous solution（2 wt%Fe,on the basis of the weight of support）and followed by drying and calcination to obtain 2Fe-CuOx/Cupronickel-foam catalyst.2Fe-CuOx/Cupronickel-foam could provide 90.4%ethanol yield at 270 ℃,WLHSVDMO of 0.44 g gcat^-1 h^-1,2.5 MPa and H₂/DMO mole ratio of 180.The reaction route of DMO to ethanol is that DMO hydrogenation to methyl glycolate（MG）,MG to EG and methyl acetate（MA）,and further to ethanol.Adding 2 wt%Co to 2Fe-CuOx/Cupronickel-foam could further improve the ethanol yield to 93.9%and was stable for 200 h.NH3-TPD,XPS and H₂-TPR results illuminated the synergistic effect nature of Fe-Co-Cu ternary active sites for DMO hydrogenation to ethanol:（1）Increased Cu+ content associated with the La₂O₃ and Lewis acidity of FeOx contributed to activating the ester groups of DMO and MG,thereby leading to more EG formation at lower temperature（190-250 ℃）;（2）Lewis acidity of FeOx promoted hydroxy of EG hydrogenation to ethanol,and also hydroxy of MG hydrogenation to MA and further hydrogenation to ethanol at higher temperature（250-310 ℃）;（3）Co additive increased Cu+ content and improved the activation of ester group of MA,and thereby leading to more ethanol formation.FeNi-LDHs could be in-situ grown onto the Ni-foam via hydrothermal method.Ni-foam@FeNi-LDHs exhibited 97.3%ethanol yield and was stable for 200 h at 290 ℃,WLHSVDMO of 0.44 g gcat^-1 h^-1,2.5 MPa and H₂/DMO mole ratio of 180.The reaction route of DMO to ethanol is that DMO hydrogenation to MG,MG to EG and MA,EG further to ethanol,and MA via acetaldehyde（HAc）to ethanol。NH3-TPD and XPS results illuminated the synergistic effect nature between Lewis acid and Ni0 sites:（1）Hydrogenation of DMO,MG and MA depended on the synergistic effect between medium/strong acid site(FeOx/Ni²⁺)and Ni0 site,in which medium/strong acid site was responsible for the activating easter group and Ni0 site for activating H₂;（2）Hydroxy of MG and EG hydrogenation depended on the synergistic effect between weak/medium/strong acid site(Fe0/FeOX/Ni²⁺)and Ni0 site,in which weak/medium/strong acid site was responsible for the activating hydroxy and Ni0 site for activating H₂.（3）Al-fiber structured Fe-Mn-K catalysts for Fischer-Tropsch to lower olefinsThin shell（-0.5 μm）nanosheet y-Al₂O₃（ns-Al₂O₃）was endogenously grown onto the Al-fiber felt with 3D open network structure and good mass/heat transfer properties via steam-only oxidation followed by calcination process.K,Mg and Zr modified Al-fiber@ns-Al₂O₃@Fe-Mn catalysts were prepared by incipient wetness impregnation（organic solvent assistance）method.K modified catalyst owned better reducibility/carbonization properties and optimum basicity,thereby leading to the best FTO performance.Al-fiber@ns-Al₂O₃@Fe-Mn-K catalyst delivered 90%CO conversion,40.0 wt%lower olefins selectivity,lower parafins/lower olefins（O/P）of 4.6 and 15.7 wt%CH4 selectivity at 350 ℃,4 MPa and GHSV of 10000 mL g^-1 h^-1,moreover this catalyst exhibited a high FTY of 206.9 μmolCO gFe-’1 s^-1,which was evidently higher than most reported catalysts.Al-fiber@ns-Al₂O₃@Fe-Mn-K catalyst possesses a thin shell（0.5 μm）,large void volume（90 vol%）,abundant macropores and mesopores,high surface-to-volume ratio and a low pressure drop,which could intensify the mass transfer and eliminate the diffusion limitation,and thereby delivering a high CO conversion whilst maintaining high lower olefins selectivity and low CH4 selectivity at high GHSV and pressure.Because of the excellent heat conductivity of Al metal,we believe that our microfibrous structured Al-fiber@ns-Al₂O₃@Fe-Mn-K catalyst can provide a significant enhancement of the intrabed heat transfer.Al-fiber@ns-Al₂O₃@Fe-Mn-K catalysts were prepared via surface impregnation combustion method using Al-fiber@ns-Al₂O₃ core-shell composite.The effect of combustion atmospheres,including air,N₂,and N₂ followed by air（N₂-air）,on the catalytic performance was investigated detailedly.Al-fiber@ns-Al₂O₃@Fe-Mn-K（air）catalyst exhibited the highest CO conversion of 89.6%and a high FTY of 206.0 μmolCO gFe^-1 s^-1,and especially the lower olefins selectivity of 41.1 wt%and O/P of 5.4 were higher than those of Al-fiber@ns-Al₂O₃@Fe-Mn-K catalyst prepared by incipient wetness impregnation（organic solvent assistance）method at 350 ℃ and 4 MPa using a high GHSV of 10000 mL g^-1 h^-1.TEM,XRD,H₂-TPR and XPS results indicated that combustion atmospheres played a role in modulating the particle size of Fe-Mn-K oxide particles,thereby resulting in different FTO performances.Al-fiber@ns-Al₂O₃@Fe-Mn-K（N₂）and Al-fiber@ns-Al₂O₃@Fe-Mn-K（N₂-air）showed smaller particle size of 3-4 nm and suffered from deteriorated reducibility and carburization properties due to the strong support-metal interaction,consenquently leading to the poor activity.Al-fiber@ns-Al₂O₃@Fe-Mn-K（air）showed particle size of 6 nm with better reducibility and carburization properties thereby leading to the optimum performance.