Effects Of Rare-earth Doping On The Textural And Catalytic Properties Of Copper-manganese Catalysts For Water-gas Shift Reaction

The effects of Rare species, lanthanum (La) doping amount and anion types onstructure, thermal stability and catalytic performance of Cu-Mn catalysts prepared byco-precipitation were characterized by X-ray diffraction, low temperature N2adsorption/desoption, temperature-programmed reduction, temperature-programmedreduction of oxidized surfaces, temperatue-programmed desorption and tested forwater-gas shift (WGS) reaction.Doped with rare earth elements had a certain impact on the low-temperaturecatalytic performance from200℃to300℃, the La, Ce and Er doping significantlyimproved the catalyst activity. Rare-earth-doped samples did not change the maincrystalline phase Cu1.5Mn1.5O4, but minor peaks of CuO were also found. After the shiftreactions, the spinel structure of all samples was destroyed, and Cu and Mn+2O wereformed in all samples, except Y-doped sample in which CuO are also detected. Inaddition undoped samples and Y-doped samples exhibited obvious characteristic peaksof MnCO3. TPR showed that more amorphous CuO were dispersed on surface ofun-doped、Pr and Y samples, moreover, doped La, Ce and Er samples had higher surfacephase reduction and bulk phase reduction closely combinated with oxygen vacancy ofCu-Mn solid solution. Doped rare earth elements had a different degree of influence onCO2adsorption capacity, doped La, Ce and Er samples have similar CO2adsorptionstrength, among them the La sample showed the highest desorption amount.Lanthanum (La) doping amount had a greater impact on the structure and propertiesof copper (Cu)-manganese (Mn) catalysts for the water-gas shift reaction. The mainphase of all calcined samples is the spinel phase Cu1.5Mn1.5O4, the samples with morethan or equal to3.0%La-doped content also found CuO phase, after the shift reactions,the spinel structure was decomposed into Cu and Mn+2O, moreover, the CuMn/La-m(0.0,0.2,0.5) samples of less La doping exhibited characteristic peaks of MnCO3. Thesamples doped with0.2%and0.5%La significantly improved the catalyst reductionproperty, uniformly distributed Cu and Mn components, and has a great synergistic effectthat increased surface Cu dispersion, and the CO2adsorption capacity is moderate,consequently, the catalytic property in the WGSR, especially the CuMn/La-0.5samples exhibited the most obvious effect. When the La content exceeds3%, the basic sitesincreased with the increase in La content, whereas CuMn/La-10samples displayed strongCO2adsorption, some active sites were covered, resulting in low catalytic activity.The structure and catalytic properties of Cu-Mn catalysts are closely related to theanionic species present in the systems. The main phase of CH3COO, Cl, NO3, and SO4samples was spinel Cu1.5Mn1.5O4metal solid solution, which was reduced to Cu andMnO after shift reactions, among them CH3COO, NO3and SO4samples showed a clearMnCO3characteristic diffraction due to CO2was adsorbed and activated. The CH3COOand NO3sample contained a consistent dispersion of Cu and Mn, which showedhomogeneous surface chemical properties, good metal synergistic effects, gooddispersion of surface Cu, and good thermal stability and reactivity at low-temperatureWGS reactions. Although the SO4sample had a specific surface Cu dispersion, itschemical properties were heterogeneous. The synergistic effect of Cu and Mn in the SO4sample was poor, leading to poor catalytic activity. The Cl sample due to the reduction ofCu which was tightly coupled with oxygen vacancies in the surface and bulk phases ofthe Cu-Mn solid solution was difficult, the synergistic effect of Cu and Mn was poor, anddisplayed weak CO adsorption, resulting in poor activity.