The alkaline earth metal stannates MSnO3 (M = Ca, Sr, and Ba) photocatalysts with different morphologies are successfully prepared by hydrothermal method and their photocatalytic activities are evaluated by photocatalytic reforming of ethanol/water solution to hydrogen.

As a class of natural clay minerals, the special surface characteristic of the negatively charged outer surface and the positively charged inner lumen enables halloysite to be of potential interest for catalytic applications. In this work, thermal treatment and modification with cetyltrimethylammonium bromide made the outer surface of halloysite hydrophobic, which resulted in the selective loading of palladium on the hydrophilic inner surface of halloysite. The designed site-oriented loading endowed catalysts with the desired structure and favorable properties for methane combustion. Because of the uniformly dispersed palladium particles (ca. 2 nm), a suitable ratio of Pd2+/Pd4+, better reducibility, and appropriate surface acidity, the tailored catalyst exhibited a remarkably higher activity with the T 99 decreasing from 620 °C (unmodified catalysts) to 425 °C. More importantly, the stabilized palladium species could resist sintering and the diminishing of hydroxyl groups on the surface weakened the interaction with water, invoking an excellent long-term/cyclic stability and water resistance for methane combustion.

Making use of synergy between urea and citric acid, a core–shell Pd@CeO 2 catalyst with spherical morphology was facilely synthesized by a hydrothermal method. The formation mechanism of the core–shell structure in the presence of citric acid and hydrogen peroxide was studied. Results showed that the Pd@CeO 2 catalyst exhibited high catalytic activity in methane oxidation. Pd nanoparticles were well stabilized by CeO 2 shell encapsulation, resulting in high stability of the catalyst. A high CH 4 conversion of 99% was retained after 50 h on-stream reaction at 500 °C. Additionally, many tiny pores on the CeO 2 shell surface were beneficial for the full contact between reactants and active components. Pd nanoparticles were highly dispersed inside the shell, improving the utilization efficiency of active components. The results also demonstrated that the Pd species in the catalyst existed in the form of oxidation state, mainly in PdO (ca. 66.6%), which played an essential part in methane combustion.

Composite oxide nanoparticles are promising candidates for catalytic applications to reduce the usage of expensive noble metals. However, the associated inferior low-temperature activity imposes major challenges on the rational design and modulation of compositions. Herein, we reported for the first time the successful synthesis of Co 3 O 4 −In 2 O 3 composite oxides with the nanoparticle size of 10−20 nm for methane combustion via a modified precipitation method adopting the organic base N-butylamine as a precipitator to eliminate the negative effects resulting from conventional inorganic base precipitators. The doped In 3+ would first occupy octahedral sites of the spinel Co 3 O 4 and then tetrahedral sites, resulting in the increase of Co 2+ ratio on the surface when the doped molar ratio (n In ) was 0−0.2 and decrease with excessive doping (n In of 0.2−0.4). The increment of Co 2+ ratio was essential for the formation of abundant reactive oxygen species, improvement of reducibility, and optimization of surface acidity, which synergistically contributed to superior catalytic activity with a T 99 of 395 °C. The catalytic activity of the tailored Co−In-0.2 nanocatalyst is among the best of the state-of-the-art Co-based catalysts; meanwhile, it also exhibits excellent stability and water resistance.

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