(328h) Stabilized CuO for Methanol Steam Reforming to Produce Hydrogen

Methanol steam reforming (MSR) to produce hydrogen is a promising technology for onboard fuel cell applications. Among all catalysts for MSR, copper-based catalysts effectively convert methanol into hydrogen with low selectivity toward CO. However, thermal sintering of Cu occurs at temperatures above 227°C. Epitaxial anchoring of metal nanoparticles (NPs) provides a feasible route to alleviate sintering of metal NPs. Deposition of carbonaceous species over surfaces of Cu NPs is another deactivation process. Oxidative MSR, accomplished by introducing a small amount of O₂ into the feed gas mixture, reduces the deposition of surface species and thus increases the catalyst stability. Copper-containing precursor species were uniformly deposited onto ZnO nanowires (NWs) via an electrostatic-adsorption-assisted deposition process. A rapid calcination treatment provided the final catalyst. Atomic-resolution HAADF-STEM images of the as-prepared CuO/ZnO NW catalyst reveals an epitaxial relationship between the CuO NPs and the ZnO NWs: ZnO [11-20] (0002)∥CuO [1-10] (111). The methanol conversion rate and hydrogen yield were dropped about 30% after 20 hours at a reaction temperature of 260°C. The catalyst activity, however, was fully recovered after an oxidative treatment, suggesting that sintering of Cu NPs was not likely the reason for deactivation. Since reduction treatment may not fully reduce CuO to Cu, we speculate that the epitaxial relationship between CuO and ZnO may retained during MSR. Raman spectroscopy confirmed deposition of carbon after 12h of MSR reaction, leading to catalyst deactivation. When ~ 2 vol% of O₂ was added to the reaction gas mixture, coke formation was avoided. Oxidative MSR reaction seems provide a reaction condition that alleviate coke deposition and Cu sintering on CuO/ZnO NW catalyst.