Due to the complexity of the structure–activity relationship of the CuAl 2 O 4 spinel catalyst, optimization of the catalyst structure is a great challenge. In this paper, three different CuAl 2 O 4 spinel catalysts were prepared by the solid-phase method using copper hydroxide, copper nitrate, and copper oxide as the copper source, respectively, to study the difference in the structure of CuAl 2 O 4 spinel catalysts induced by the raw materials and the catalytic behavior for CO hydrogenation. The structure of CuAl 2 O 4 spinel catalyst was characterized by XRD, BET, SEM, TEM, H 2 -TPR and XPS. The activity of CO hydrogenation over the CuAl 2 O 4 spinel catalyst without pre-reduction was evaluated in the slurry reactor. The results demonstrated that different copper sources had obvious influence on the CuAl 2 O 4 spinel texture properties, surface enrichment degree, as well as decomposition and reduction ability, which further regulated the ratio of Cu + /Cu 0 and thus affected the catalytic performance, especially the alcohol distribution. The CuAl 2 O 4 spinel, employing copper hydroxide as the copper source, showed better selectivity of C 2+ OH, which was assigned to a higher ratio of Cu + /Cu 0 , along with larger pore size and pore volume. Moreover, the synergistic effect between Cu 0 and γ-Al 2 O 3 improved the selectivity of dimethyl ether.
Hydrogen generation via methanol steam reforming is a promising method for producing renewable energy. In this work, a series of Mn 2+ -substituted CuAl 2 O 4 spinels were prepared by solution combustion method, and the crystal structure, micromorphology, chemical constitution, reduction behavior, acidity, specific surface area and surface chemical state of the spinels were comprehensively characterized by various equipments. The obtained spinels were washcoated on Cu foams to prepare monolithic catalysts, and the catalytic performance of the catalysts was evaluated in a methanol steam reforming microreactor. Compared with the binary Cu–Al spinel, the Mn 2+ substitution led to a decrease in the particle size, a change in the chemical composition and reduction behavior, a decline in the acidity, an increase in the specific surface area, and an improvement in the surface chemical state. As a result, the release rate of active Cu from the Mn-containing CuAl 2 O 4 spinel was significantly slowed down and the formed nanoparticles were fine, which was believed to be in favor of maintaining a stable catalytic performance longer. Among the prepared catalysts, the monolithic catalyst loaded with Cu 0.4 Mn 0.6 Al 2 O 4 exhibited the highest activity and stability. The findings of this work suggested that introducing Mn 2+ might be a promising way to regulate the Cu releasing property for obtaining a better sustained release catalyst system.
Herein, macroporous CuAl2O4 spinel monoliths derived from ionic precursors were successfully synthesized via a sol–gel route in the presence of propylene oxide (PO) and poly(ethylene oxide) (PEO). PO and PEO cooperatively control the sol–gel transition and phase separation of the system to form gels with a phase-separated macrostructure. The resultant xerogel exists in the form of a monolith and possesses interconnected macroporous channels and co-continuous dense skeletons composed of amorphous Al(OH)3 and Cu2(OH)3Cl. Heat-treatment allows the formation of the single crystalline phase CuAl2O4 spinel without the destruction of well-defined interconnected channels, and the CuAl2O4 spinel monoliths with a macropore size of 0.5–1 μm and porosity of 55–70% can be obtained after heat-treatment. In this study, three anionic dyes and two cationic dyes were selected as adsorbates to investigate the selective adsorption ability of the resultant monoliths. Results indicate that the as-prepared CuAl2O4 spinel heat-treated at 600 °C shows a high affinity and adsorption rate towards the anionic dyes congo red (∼100%) and methyl blue (∼81.8%) within 10 min except towards methyl orange (∼25.5%); thus, the abovementioned spinel can be used for the efficient and selective adsorption of certain anionic dyes from a binary cationic–anionic dye system or fast separation of methyl orange (MO) from a double anionic dye system.
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