Dramatic Effects of Gallium Promotion on Methanol Steam Reforming Cu–ZnO Catalyst for Hydrogen Production: Formation of 5 Å Copper Clusters from Cu–ZnGaO_x

Abstract

A new class of copper, zinc, and gallium mixed oxides (CuZnGaO x ) with different chemical compositions obtained by a coprecipitation technique is identified as a highly active catalyst for the low-temperature, direct steam reforming of methanol to supply hydrogen gas to portable fuel cell devices. Their catalytic activity and selectivity are found to be critically dependent on the copper surface area, catalyst structure, and metal–support interaction, etc. As a result, temperature-programmed reduction has been used to investigate the copper ion reducibility and resulting copper speciation; N2O chemisorption and advanced microscopies to determine specific copper surface area, dispersion, and particle size; XRD to investigate the catalyst structure; EPR spectroscopy to probe the environment of Cu2+ species; and AC impedance spectroscopy to probe the mobility of trapped ions in solids. It is proposed that Ga incorporation into Cu–Zn oxide leads to the formation of a nonstoichiometric cubic spinel phase containing interstitial Cu+ ions, which can produce in situ a high population of extremely small 5 Å copper clusters at high dispersion on a defective ZnGa2O4 surface for effective catalysis.

Synthesis of stable Cu-MCM-41 nanocatalysts for H2 production with high selectivity via steam reforming of methanol

“…However, with further increase in Cu loading to 20%, the dispersion of Cu dropped to 53.1%. This decrease in dispersion with increase in Cu loading is consistent with the results of Tong et al [59] and Lopez-Saurez et al [37] for Cu/ZnGaO x and Cu/ Al 2 O 3 catalysts, respectively. While in Cu/ZnGaO x an increase in Cu loading from 15% to 60% catalyst decreased %Cu dispersion by about 72% [59], for Cu/Al 2 O 3 catalyst it continuously decreased from 76% to 14% when Cu loading was increased from 1% to 15% [37].…”

“…This decrease in dispersion with increase in Cu loading is consistent with the results of Tong et al [59] and Lopez-Saurez et al [37] for Cu/ZnGaO x and Cu/ Al 2 O 3 catalysts, respectively. While in Cu/ZnGaO x an increase in Cu loading from 15% to 60% catalyst decreased %Cu dispersion by about 72% [59], for Cu/Al 2 O 3 catalyst it continuously decreased from 76% to 14% when Cu loading was increased from 1% to 15% [37]. The initial trend of increased %Cu dispersion with increased loading up to 15% can be attributed to our one pot synthesis method where Cu particles could be embedded in the silica walls decreasing the available surface Cu atoms.…”

Hydrogenation of biomass-derived compounds containing a carbonyl group over a copper-based nanocatalyst: Insight into the origin and influence of surface oxygen vacancies

“…2), an intensive signal at 345 mT is associated with Cu 2+ ions in a tetrahedral environment within the CuO-Al 2 O 3 solid solution [53]. As for MMO-1.5, there is only a large and broad signal around 567.8 mT, which is assigned to Cu 2+ ions in an octahedral environment within the cubic spinel structure [54]. MMO-0.5 and MMO-1 samples display a broad signal between 345 and 567.8 mT, suggestive of the coexistence of CuMnAl 2 O 4 and CuO in calcined samples.…”

An Application of Microemulsion Method for Synthesis of Copper-Zinc Materials

“…According to Fierro and coworkers the reduction temperature of copperzinc mixed oxides containing 30% CuO ranges from 150 to 200°C [10]. However pure copper oxide, as well as copper-zinc oxide systems of much lower reducibility were also widely described in the literature [11][12][13]. Agrell and coworkers prepared copper supported zinc oxide catalysts using microemulsion method, which have similar composition.…”