Preparation Of Molybdenum Carbide Based Catalyst And Its Catalytic Study On Methanol Steam Reforming For Hydrogen Production

Hydrogen production from methanol steam reforming（MSR）is an effective way to supply hydrogen to hydrogen fuel cells.In recent years,molybdenum carbide（MoC）based catalyst,as a new type of catalytic material,has shown similar catalytic performance to precious metal in the process of MSR catalytic reaction,so it has been widely concerned.In spite of this,the MoC-based catalyst still has a rapid deactivation phenomenon during the catalytic process,and the byproduct CO is too high,resulting in the MSR hydrogen production performance still cannot meet the standard required for proton membrane fuel cells.Therefore,to improve the catalytic activity and stability of MoC MSR hydrogen production and reduce the selectivity of CO byproducts has become one of the core problems to be solved urgently in the development of low temperature and high efficiency MSR hydrogen production catalysts.In this paper,the effect of different metals（Pt,Ru,Ir）doped MoC catalysts on the hydrogen production performance of methanol steam reforming was investigated.The results show that Pt/MoC has the best performance of methanol steam reforming.On this basis,the hydrogen production performance of MSR doped with different contents of Pt/MoC was investigated.The results showed that although the hydrogen production performance of Pt/MoC was enhanced with the increase of Pt content,the catalytic performance of Pt/MoC was significantly deactivated.Furthermore,the Pt/MoC catalyst was modified with different content of activated carbon.The results show that doping activated carbon can not only delay the deactivation behavior of Pt/MoC catalyst,but also significantly improve its hydrogen production activity at low temperature.The main research contents and results are as follows:1.Study on hydrogen production from methanol steam reforming by different metal doped MoCIn this paper,the MSR hydrogen production performance of 0.5Pt/MoC,0.5Ru/MoC and0.5Ir/MoC was studied.In addition,the hydrogen production performance of 0.5Pt/MoC catalyst MSR at different temperatures was investigated,and the stability of MoC catalysts doped with different metals was tested.In addition,XRD,SEM and XPS were also used to characterize and analyze the catalyst.The results show that the structure of Pt-doped MoC catalyst isα-MoC_1-x crystal phase,while Ru and Ir doping,β-Mo₂C andα-MoC_1-x crystal phase coexist.The results showed that the MSR activity of Pt/MoC catalyst was the highest,and the methanol conversion reached 40%.However,under the same conditions,the methanol conversion of Ru and Ir doped MoC-based catalysts was lower than 10%.It is concluded that for MoC-based catalysts,α-MoC_1-x with face-centered cubic（fcc）structure exhibits higher MSR hydrogen production activity thanβ-Mo₂C with hexagonal dense reactor（hcp）structure.This is consistent with the results reported in the literature.2.Study on the hydrogen production performance of methanol steam reforming with different contents of Pt doped MoCSecondly,the MSR hydrogen production performance and catalytic stability of MoC catalysts doped with different Pt content（xPt/MoC,x=0.3,0.5,1,1.5,2）were studied.Meanwhile,the xPt/MoC catalysts were characterized by BET,XRD,SEM and XPS test techniques.The characterization results show that the low content of Pt doping is conducive to the formation of moreα-MoC_1-x crystal phases,while the high content of Pt doping makes the Pt particles more likely to agglomerate.It should be emphasized that although Pt-doped MoC catalysts with different contents have good catalytic performance for methanol steam reforming,the catalyst still has rapid deactivation phenomenon during the catalytic process,and the deactivation results in low methanol conversion and hydrogen production.3.Study on the hydrogen production performance of methanol steam reforming doped with different content of activated carbon 1Pt/α-MoCIn the end,the MSR hydrogen production performance of 1Pt/α-MoC catalysts doped with activated carbon（0%,0.5%,1%,3%,5%,10%）was studied.For comparison,the MSR hydrogen production performance of the reference catalysts,α-MoC,3C/α-MoC,1Pt/C catalysts,was tested experimentally.In addition,the effects of different reaction conditions（different reaction temperature,different feed rate of methanol and water mixture,different molar ratio of methanol to water mixture）on the hydrogen production performance of methanol steam reforming were investigated,and the stability of 1Pt/α-MoC catalyst doped with different activated carbon content was tested.In the same way,BET,XRD,Raman,SEM,XPS,HAADF-STEM and EDX test methods are also used to analyze the catalyst.The characterization results showed that for 1Pt/α-MoC catalyst doped with activated carbon,doping a small amount of activated carbon not only facilitated the formation of moreα-MoC_1-x crystalline phases,but also improved the interaction between the active sites of Pt andα-MoC_1-x.The optimal 3C-1Pt/α-MoC catalyst has a methanol conversion rate of 96%and a hydrogen production rate of 177.6mmol·gcat^-1·h^-1 at the reaction temperature of 160°,and remains relatively stable within 20h.The deactivation rate of 3C-1Pt/α-MoC catalyst decreased significantly compared with 1Pt/α-MoC catalyst,although there was some deactivation behavior.In particular,the average TOF of 3C-1Pt/α-MoC catalyst reached 3465 mmol·g_cat^-1·h^-1,1.5 times that of 1Pt/α-MoC catalyst.In addition,with 3C-1Pt/α-MoC as the catalyst for hydrogen production of MSR,only a small amount of CH₄ byproducts and almost no CO byproducts were produced in the gaseous reaction products.These results indicate that the 3C-1Pt/α-MoC catalyst has excellent catalytic activity and selectivity for methanol steam reforming.