Design And Preparation Of Inverse ZrO₂/Cu Catalyst And Its Performance For Hydrogen Production From Methanol Steam Reforming

As an ideal clean energy,hydrogen has become a promising candidate to replace traditional fossil fuels and realize a low-carbon economy.Theoretically,methanol steam reforming reaction can produce high-purity hydrogen with low（no）CO,which is appropriate for vehicle-mounted or mobile hydrogen fuel cells.The copper-based catalysts are widely used in methanol steam reforming,remarkable for its inexpensiveness and attractive low-temperature MSR activity.However,it is prone to sinter and deactivate at high temperature and/or in stop-go traffic.At the same time,the developed copper-based catalyst cannot meet the requirement that the CO concentration in the product mixture gas must be lower than 20 ppm.In this paper,based on the top-down design of"Interfacial site-Interface amount-Catalytic performance",a highly-dispersed inverse ZrO₂/Cu catalytic system was obtained by oxalate sol-gel co-precipitation method.The catalysts realize the target of hydrogen production from methanol under the condition of low temperature,atmospheric pressure and free-CO.The main contents and conclusions of this paper are as follows:（1）The catalytic performance of the inverse ZrO2/Cu catalyst for methanol steam reformingHigh-perfomance ZrO₂-x/Cu catalysts were prepared by oxalate sol-gel coprecipitation method and H₂-reduction pretreatment.The optimum catalyst was prepared with the Zr/Cu molar ratio of 0.1,followed by the calcination under 450 ℃ for 3 h and reduction under 300 ℃ for 2 h.The results of catalyst evaluation show that the hydrogen production rate of ZrO₂-0.1/Cu is as high as 190 mmol g_cat^-1 h^-1,and CO₂selectivity is 100%,with CO and CH₄ concentrations below the detection limit of GC-TCD(200 ℃,weight hourly space velocity（WHSV）of 10 h^-1,steam-methaol molar ratio（S/M）of 1.0).In addition,the catalyst remians active in the stability test up to 200-h,showing excellent MSR activity and stability.（2）The catalytic mechanism of the inverse ZrO₂/Cu catalyst for methanol steam reformingA series of structural and surface characterizations were carried out on the inverse ZrO₂-x/Cu catalysts.The reduced ZrO₂-0.1/Cu shows inverse structure of t-ZrO₂/Cu,in which highly-dispersed t-ZrO₂ nanoparticles contact with the Cu substrate to form a large number of ZrO₂-Cu interfaces.During the reaction process,ZrO（OH）-Cu⁺/Cu structure is in-situ formed on the interface of ZrO₂-Cu and plays a key role in MSR reaction.Specifically,CH₃OH dehydrogenates at Cu⁺/Cu sites to form HCHO^*;while H₂O dissociates and adsorbs at t-ZrO₂ sites to form Zr-OH.HCHO^*reacts with interfacial Zr-OH to transform into HCOOH^*,and finally decomposes to produce CO₂and H₂.Through the comparison of ZrO₂-0.1/Cu catalyst and the comparative catalysts in terms of catalyst evaluation,the apparent activation energy determination,and the TPD/TPSR-tests,it is further proved that the synergistic catalysis of ZrO₂-Cu interface is the key to achieve high activity and selectivity in MSR reaction.