Influence Of The Cu-based Catalyst Precursor Phase Transition For Slurry Methanol Synthesis

The liquid phase methanol synthesis process is one of the key technologies at poly-generation on the basis of coal and natural gas, but Cu-based catalyst is easy to heat inactivation and shorter life expectancy, has been plagued by industrial applications. Recent studies show that microwave radiation on the CuO/ZnO/Al2O3catalyst precursors has a greater influence on the formation and micro-structure of catalysts, in particular, the introduction of the microwave radiation in the aging process of preparing precursors, it is possible to promote the isomorphous substitution, in favor of (Zn,Cu)5(CO3)2(OH)6crystalline phase is formed in the precursors, after calcining the precursors, are conducive to the formation of a solid solution of CuO-ZnO, and increase the degree of dispersion of the active metal Cu, after reducing of the Cu-based catalysts are not easily inactivation and Cu-grains difficult to reunite, significantly improve the stability of the catalyst.Firstly, the copper and zinc hydroxycarbonates precursors with different Cu/Zn atomic ratios were prepared by the co-precipitation method in this article, the ratio of Cu to Zn affected the catalyst precursor phase transition was systematically studied, the results showed that:(1) No Addition of Zn2+into raw materials, the single phase Cu2CO3(OH)2was to exist on precursors, when the zinc atomic was added to the raw materials, isomorphous substitution process occured on phase composition of precursor, there has been the one new phase (Cu,Zn)2(CO3)(OH)2; When the ratio of Zn to Cu at33/67or less, the mainly phase composition of precursors were (Cu1-x,Znx)2(CO3)(OH)2(x=0.1,0.2,0.25,0.3).(2) No Addition of Cu2+into raw materials, the single phase Zn5(CO3)2(OH)6was to exist on precursors, when the copper atomic was added to the raw materials, the substitution of Zn2+in Zn5(CO3)2(OH)6compound by Cu2+and increased the content of (Zn,Cu)5(CO3)2(OH)6phase in the precursor, when the ratio of Cu to Zn at40/60or less, the mainly phase composition of precursors were (Zn1-x,Cux)5(CO3)2(OH)6(x=0.2,0.25,0.3,0.4).(3) When the ratio of Cu to Zn was greater than40/60, was less than67/33, the phase composition of precursors were (Cu1-x,Znx)2(CO3)(OH)2and (Zn1-x,Cux)5(CO3)2(OH)6at the same time.On a combination of the previous section, microwave radiation was introduced into the preparation processes in this section, Constant microwave power and aging temperature were160W and80℃, respectively, the effect of aging time including in5,10,15,30and60min on the catalyst precursor phase transition was studied; as well as Constant microwave time and aging temperature were15min and80℃, respectively, the effect of microwave power including in80,160and240W on the catalyst precursor phase transition was studied; XRD, FT-IR, DTG, H2-TPR and XPS were used to examine the influences of microwave radiation power and microwave radiation time on the crystal phase composition and transition of precursors were further investigated. The results as follow:(1) Compared with the precursor aged for5min under microwave radiation possesses the phase structure of the catalyst precursor was basically the same as the precursor aged for1h without microwave radiation, the phase composition of precursors were rosasite (Cu,Zn)2(CO3)(OH)2and aurichalcite (Zn,Cu)5(CO3)2(OH)6at the same time, it was illustrated that the introduction of microwave radiation was able to accelerate the speed of the precursor isomorphous substitution.(2) The experimental results showed that the crystalline degree and crystal structure of (Zn,Cu)5(CO3)2(OH)6became higher and perfect, the substitution of Zn2+in Zn5(CO3)2(OH)6compound by Cu2+has been basically completed and the formation of (Zn,Cu)5(CO3)2(OH)6within microwave power and aging time were160W and15min, respectively.(3) The calcined catalyst had strong interaction between CuO and ZnO and the formation of a solid solution of CuO-ZnO, well dispersed CuO crystal particles, and high surface CuO content. In the aging process the precursor aged for15min under microwave radiation exhibited the highest methanol space-time yield (STY) and the lowest deactivation rate were305.07g/(kg-h) and0.12%/d, respectively; Compared with the catalyst prepared without microwave radiation, the STY and deactivation rate of the catalyst under microwave irradiation were increased and decreased by8.3%and42.86%, respectively.CO2was added to the mother liquor in the aging processes by conventional heating at the same time, it could help to keep pH close to neutral, and generated CO32-ions, thus facilitating Zn2+precipitate and promoting Cu2+into Zn5(CO3)2(OH)6lattice substitution of Zn2+formation the aurichalcite(Zn,Cu)5(CO3)2(OH)6, leading to the improvement of content in precursors. the best catalytic performance including the methanol space-time yield (STY) and the stability. While the volume flow of CO2was40ml/min, the methanol space-time yield (STY) and deactivation rate of the catalyst were302.45g/(kg·h) and0.15%/d, respectively; Compared with the catalyst prepared without adding CO2in the aging process, there were a certain degree of improved to the aspects of the catalyst activity and the stability.