Microfibrous Structured Pd-ZnO Catalysts For Methanol Steam Reforming To Produce Hydrogen

Polymer electrolyte membrane fuel cells (PEMFCs) as a high-efficient and clean power-generation technology have a wide application prospect in car power systems and power station. Hydrogen generation through steam reforming of methanol at a low temperature with simple following purification steps is an ideal portable hydrogen fuel cell reaction process. The integration design of catalyst and reactor in portable hydrogen production system not only can solve the heat/mass transfer problems encountered in the traditional fixed-bed reactor but can also overcome channel flow caused by the aggregation of particle catalysts. Thus, the goal of the present work is to develop the micro-structured catalyst and reactor technology with enhanced heat/mass transfer property in portable hydrogen production. To accomplish this goal, Pd-ZnO composite supported on the thin-sheet three-dimensional (3D) network of metal fibers have been developed for H2 production from methanol steam reforming (MSR) reaction.The monothic Pd-ZnO/brass-fiber catalysts were prepared for the MSR reaction, by the galvanic deposition of Pd onto brass fibers followed by ZnO-doping through impregnation method. The optimized composition of this microfibrous-structured catalyst is Pd loading of 2 wt% with Pd/Zn mole ratio of 1/3, while the optimal calcination temperature and reduction temperature is 350 ℃ and 450 ℃, respectively. This catalyst is not so active at low temperature but a high selectivity of CO2 is obtainable even at a high temperature, when using a feed of CH3OH/H2O=1/1.2 (mol/mol) at WHSV of 5.4 h’1. With the increased reaction temperature from 350 ℃ to 600 ℃, the conversion of methanol increases from 60% to 99% with the selectivity of CO2 higher than 90%.The monothic Pd-ZnO/Al-fiber catalysts were prepared by the galvanic deposition of Pd onto Al-fibers followed by by ZnO-doping through impregnationmethod. The optimized composition of this microfibrous-structured catalyst for the MSR reaction is Pd loading of 3 wt% with Pd/Zn mole ratio of 1/15. The optimal calcination temperature and the reduction temperature is 300 ℃ and 450 ℃, respectively. A methanol conversion of >80% can be obtainable while the volume content of CO in the H2-rich tail gas is only 0.45 vol% at reaction temperature of 350 ℃, using a feed of CH3OH/H2O=1/1.2 (mol/mol) at WHSV of 5.4 h-1.A high-performance structured Al-fiber@meso-Al2O3@3Pd-11.5ZnO catalyst is developed by impregnating a thin-sheet Al-fiber@meso-Al2O3 with a mixture aqueous solution containing appointed amount of Pd and ZnO. For this catalyst, the optimal calcination and reduction temperatures are confirmed to be 300 ℃ and 450 ℃, respectively. In comparison with aforementioned structured Pd-ZnO catalysts, the Al-fiber@meso-Al2O3@3Pd-11.5ZnO catalyst exhibits good low-temperature activity. At 300 ℃ with WHSV of 2.7 h-1, a high methanol conversion of 96.9% is achievable and the volume content of CO in the H2-rich tail gas is only 0.45 vol%. The catalyst is stable for at least 300 h, showing good conversion (> 95%) and CO2 selectivity (> 85%) maintenance through the entire testing. Moreover, interaction of PdZn alloy and ZnO is discussed and correlated with the catalyst performance.