Search

Cu-Al spinel oxide, which contains a small portion of the CuO phase, has been successfully used in methanol steam reforming (MSR) without prereduction. The omission of prereduction not only avoids the copper sintering prior to the catalytic reaction, but also slows down the copper-sintering rate in MSR. During this process, the CuO phase can initiate MSR at a lower temperature, and CuAl2O4 releases active copper gradually. The catalyst CA2.5-900, calcined at 900 °C with n(Al)/ n(Cu)=2.5, has a higher CuAl2O4 content, higher BET surface area, and smaller CuAl2O4 crystal size. Its activity first increases and then decreases during MSR. Furthermore, both fresh and regenerated CA2.5-900 showed better catalytic performance than the commercial Cu-Zn-Al catalyst. [ABSTRACT FROM AUTHOR]

Cu–Al spinel oxide (CA) as a sustained release catalyst has been successfully used in methanol steam reforming and it is highly required to improve its catalytic performance. Here, surface modification of the CA with various MgO loadings was performed. Characterization results showed that MgO dopant had strong interaction with the CA, resulting in a substantial change of the surface microstructure. Importantly, a small portion of lattice Cu2+ was phased out while partial Mg2+ cations incorporated into the spinel structure, giving rise to a variation of the cation distribution. Consequently, the change of the Cu2+ surrounding environment made it become hard to be reducible, thus the doped catalysts showed a lower copper releasing rate and smaller copper particles. Then, the activity and stability were enhanced when a suitable amount of MgO was highly dispersed. Excess amount of crystalline MgO gave rise to easy coking that resulted in an inferior catalytic performance. Image 1 • Cu–Al spinel sustained release catalyst was modified by MgO. • Variation of surface microstructure favored formation of small Cu nanoparticles. • MgO modification retarded copper releasing rate, enhancing catalytic stability. • A suitable amount of MgO promoted the catalytic performance. • Excess amount of MgO doping resulted in poor catalytic performance due to coking. [ABSTRACT FROM AUTHOR]

• Hydrogenolysis of HMF to DMF was catalyzed by reduced NiZn catalyst. • The highest 99% DMF yield was obtained at 180 °C for 4 h under 2 MPa H 2. • The formation of NiZn alloy in reduced NiZn-450 catalyst exhibited high C-O hydrogenolysis ability. • An outstanding stability was achieved for reusing 9 times. The transformation of biomass to liquid fuels and chemicals is of great interests. Herein, a series of reduced NiZn-CT (CT represents calcination temperature) catalysts with flower-like morphology and uniform particle sizes were prepared by co-precipitation method and used for hydrogenolysis of 5-hydroxymethylfural (HMF) to 2,5-dimethyfuran (DMF). The characterizations evidenced the formation of NiZn alloy phase in the catalysts through the strong metal-support interaction (SMSI), which had high C-O hydrogenolysis ability. The synergy of hydrogenation and C-O hydrogenolysis is essential for HMF to DMF, and we surprisingly found that this synergistic effect can be achieved just by controlling calcination temperature to regulated SMSI between Ni and ZnO. By this way, 99% DMF yield was gained at 180 °C for 4 h under 2 MPa H 2 over reduced NiZn-450 catalyst. More importantly, the active centers of this Ni/ZnO catalyst exhibited outstanding stability. There was no significant decrease in activity after reusing 9 times. The current research provided an easy-made catalytic system for HMF hydrogenolysis. [Display omitted] [ABSTRACT FROM AUTHOR]

In order to find a method to synthesize spinel solid solution at low temperature, in this paper, pseudo-boehmite and copper nitrate were used as raw materials, and citric acid was used as accelerator for the first time, the Cu 1−x Al 2.5 spinel solid solutions were synthesized by ball milling treatment of the solid mixture and then calcined at elevated temperatures. The obtained materials were characterized by X-ray diffraction (XRD), Brunner−Emmett−Teller (BET) measurements, H 2 -temperature programmed reduction (H 2 -TPR), infrared (IR) and thermogravimetric methods (TG), and the mechanism of citric acid promoting the synthesis of the spinel solid solution was suggested. The results show that an optimal amount of citric acid can significantly promote the formation of the spinel structure, thus substantially decreasing the synthetic temperature from the above 900 °C–700 °C. At 700 °C, the preparation without the accelerator resulted in small amount of the spinel solid solution, while the use of accelerator gave rise to 82.96% spinel solid solution. Importantly, the Cu 1−x Al 2.5 spinel solid solution prepared at 700 °C demonstrates the best sustained release catalytic performance, and the catalytic activity reached more than 90% and remained stable within 50 h. The findings of this report might be provide guidance for the solid phase preparation of catalysts at relatively lower temperatures, thus facilitating the commercialization of the sustained release catalyst system. For the preparation of Cu–Al spinel by ball milling, citric acid was used as an accelerator for the first time, effectively decreasing the synthetic temperature. [Display omitted] • Citric acid was used as an accelerator for the first time. • The synthetic temperature of Cu–Al spinel by was decreased. • Possible mechanism for such an acceleration has been suggested. • The obtained solid solution can be used as a sustained release catalyst. [ABSTRACT FROM AUTHOR]

• Green synthesis of Cu 1−x Mg x Al 3 spinel is achieved by solid-phase reaction method. • Replacing partial Cu by Mg induces a substantial redistribution of the cations. • The ternary spinel tends to produce small nano copper during catalytic process. • Cu 0.9 Mg 0.1 Al 3 catalyst achieves the best catalytic performance. • The copper releasing behavior can be regulated by changing the Mg content. A versatile and green method for the synthesis of an efficient catalyst applied in methanol steam reforming is promising in view of clean energy production. Cu 1−x Mg x Al 3 ternary spinel oxide catalysts have been prepared by a one-pot solid-phase reaction method using Cu(OH) 2 , Al 2 O 3 ·xH 2 O and MgCO 3 as the raw materials. The structure, reducibility, surface chemical state, and the aluminum ion distribution are comprehensively characterized by XRD, UV–vis, XPS, H 2 -TPR, N 2 O chemisorption, and 27Al MAS NMR techniques. The performances of the catalysts in methanol steam reforming are evaluated. Compared with binary Cu-Al spinel, the incorporation of Mg into the spinel lattice results in the change of Al3+ cation distribution between tetrahedral and octahedral sites, and thus the variation of copper surrounding environment can be inferred. Consequently, the copper releasing rate from the Mg containing spinel structure declines substantially, which is believed to be in favor of maintaining a stable catalytic performance longer. Besides, the ternary spinel oxide might facilitate the in-situ formation of smaller nano copper metals compared to CuAl 3 binary spinel catalyst. Among all the catalysts, Cu 0.9 Mg 0.1 Al 3 presents the highest activity as well as the best catalytic stability. The findings of this report suggest that introducing a foreign cation into the Cu-Al spinel structure might be a promising way to regulate the copper releasing property for achieving a better sustained release catalyst system. [ABSTRACT FROM AUTHOR]