Poor catalytic activity and stability are primary defects of traditional Pd/Al 2 O 3 catalysts for the low-temperature methane combustion. Herein, we developed a facile way to synthesize a MgAl-LDHs derived MgAl 2 O 4 spinel with good crystalline lattice and high surface area, which was used as support of Pd-based catalysts. Catalysts with Mg/Al ratio of 1/3 presented the highest methane combustion activity. It was found the well-crystallized MgAl 2 O 4 spinel promoted the dispersion and crystallization of PdO due to the strong interaction between PdO and support, and the electrophilicity and basicity originated from Mg doping suppressed the sintering of PdO particles, leading to the excellent performance of Pd/MgAl3. Moreover, these factors also inhibited the formation of surface OH- species, therefore, improved the water resistance. Such a synthesis strategy of the Pd/Mg x Al y derived from LDHs and the roles of MgAl 2 O 4 spinel could pose some meaningful directions for developing high-efficient Pd-based catalysts for the low-temperature methane combustion.
Zijian Yuan,Anuj Kumar,Daojin Zhou,Junting Feng,Bin Liu,Xiaoming Sun
Even though Ni catalysts have shown promising performance in the semi-hydrogenation of ethylene, the selectivity and stability remain to be improved so that they may be used to replace expensive noble metal catalysts. Herein, an aluminate-intercalated NiMgAl-layered double hydroxide (LDH) was prepared through a facile co-precipitation approach, and then a topotactic transformation strategy was employed to convert the tailored LDH precursor to the spinel catalyst. More than 99% of the Ni/MgAl 2 O 4 catalyst's conversion was achieved toward the semi-hydrogenation of acetylene at 140 °C, with a selectivity of more than 80%. Additionally, due to high specific surface area (309 m 2 /g) with tuned acidity, this catalyst showed outstanding resistance to the deposition of carbonaceous compounds and satisfactory long-term stability during a 28 hr test. It is hoped that this study will inspire the design of supported non-noble metal materials with high activity and efficiency towards organic or organo-thermal reactions, as well as provide a basic understanding of the role and impacts of intercalated aluminates in LDH.
Petal-like MgAl 2 O 4 spinel was successfully prepared using a novel inorganic salt-assisted nonhydrolytic sol-gel method without a template and was employed as absorbent in the removal of the Congo red (CR). The effects of the inorganic salt type, heat-treatment temperature, and dwelling time on the morphology and phase composition of the petal-like MgAl 2 O 4 spinel were investigated systematically. Results indicated that when Na 2 MoO 4 was employed as the salt and the heat-treatment temperature and dwelling time were 600 °C and 5 h, respectively, the as-obtained petal-like MgAl 2 O 4 spinel exhibited a highly uniform morphology with a thickness of 19–23 nm and a length of 240–280 nm. The N 2 adsorption-desorption results revealed that the petal-like MgAl 2 O 4 exhibited a large BET specific surface area of 161 m 2 g -1 with a pore volume of 0.24 cm 3 g -1 . The growth mechanism of the petal-like MgAl 2 O 4 is believed to be the formation of a two-dimensional layered network structure by the coordination between the condensation product of the magnesium aluminium bimetallic alkoxides and the ions in the salt. The as-prepared MgAl 2 O 4 petal exhibited an effective adsorption capacity toward anionic dyes CR. The maximum adsorption capacity of CR onto the mesoporous MgAl 2 O 4 petal was found to be 572.01 mg/g, it is showed the petal-like MgAl 2 O 4 exhibit huge potential of application in the field of environmental remediation.
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