Cu-based And Zn-based Catalysts For DME Steam Reforming To Produce Hydrogen

The increasing consumption of fossil fuels inevitably leads to both of energy shortage and various environmental pollutions.So,the exploration and application of new clean energies are becoming more and more important.H2 is a kind of clean and renewable energy,which is suitable for future energy development.Dimethyl ether steam reforming?DME SR?is an efficient way to produce hydrogen.For DME SR,the development of highly efficient catalyst is crucial.The greatest challenge of the catalysts is to improve the catalytic performance,including low-temperature selectivity,stability and high-temperature activity.In this work,the composite catalysts of solid acid ?-Al₂O₃ combined with the Cu based mental catalyst or Zn based oxide catalyst were studied.The doping on catalytic properties was investigated.The BET,XRD,H2-TPR,XAFS,TPD-MS-CH3 OH,in-situ FTIR of CH3 OH,XPS and other technologies were conducted.The catalyst structure and properties were correlated.A series of CuAl Zn60-xNixO catalysts were prepared by co-precipitation method.The effect of doping amount of Ni was studied.Activity and stability tests showed that the optimum doping amount of Ni is 0.2 %.Meanwhile,the addition of Ni increases the conversion of DME and the yield of H2,and enhances the stability of the catalyst.The characterization results demonstrate that the doping of Ni species enhanced the dispersion of copper,thus decreasing its reduction temperature.Co-precipitation method was applied to prepared the Ga doped ZnO?GDZ?catalyst,and the effect of Ga doping amount on the ZnO catalyst was investigated.The appropriate amount of Ga can be doped into the lattice of ZnO,improving the electrical conductivity of the catalyst.When the Ga:Zn is 1:9,GDZ catalyst has the highest electrical conductivity.The corresponding Zn9Ga1O/?-Al₂O₃ has the highest conversion of DME?95.4 %?and the highest yield of H2?95 %?.On the basis of the results of the electrical conductivity,XPS,TPD-MS-CH3 OH,in-situ FTIR of CH3 OH,we deduced that the DME SR reaction on GDZ catalysts is an n-type reaction,of which the transformation from HCOO-to CO2 is the rate-determining step.Different amount of CuO were loaded on the Zn9Ga1 O support,which was prepared by co-precipitation.The effect of Cu loading amount on the catalysts was investigated.Activity test showed that the optimal loading amount of CuO is 10 %,and the corresponding apparent activation energy is 110 kJ·mol-1.The characterization results showed that the copper dispersion decreased from 12.0 % to 7.0 % with the increase of CuO content from 5 % to 15 %.The catalyst of 10CuO/Zn9Ga1 O has the maximum copper surface area,i.e.5.72 m2·g-1.The existence of large amounts of Cu+ is associated with the low selectivity of CO in DME SR reaction.Cu species in the catalyst promoted the activation of methanol molecules.Then,the adsorbed methanol on x CuO/Zn9Ga1 O is gradually dehydrogenation,and finally desorbed in the form of CO2.The effects of pre-reduction temperature,the loading amount of Zn9Ga1 O and the different CexZr_1-xO carrier were also investigated in DME SR.Activity tests showed that 460 °C is the appropriate pre-reduction temperature,and the activity of xZn9Ga1O/Ce0.8Zr0.2O were superior to the Ce0.8Zr0.2O and Zn9Ga1 O catalysts.The conversion of DME over 20Zn9Ga1O/Ce0.8Zr0.2O was the highest.The conversion of DME over 20Zn9Ga1O/CexZr_1-xO catalysts varied greatly at low temperatures,and the 20Zn9Ga1O/Ce0.8Zr0.2O catalyst performed the best activity.On the other hand,the occurrence of side reactions at high temperature led to the decline of H2 yield and the increase of CO selectivity.The addition of Zr enhanced the reduction ability and the mobility of surface oxygen.Compared with Zn9Ga1 O catalyst,the methanol adsorbed on 20Zn9Ga1O/CexZr_1-xO catalyst is easier to form methoxy,while the H2 and CO2 are desorbed on 20Zn9Ga1O/CexZr_1-xO catalyst.The non-significant differences of the H2 and CO2 desorption temperature lead to the similar activity of all the catalysts at high temperatures.