Scaling-Up Microwave-Assisted Synthesis of Highly Defective Pd@UiO-66-NH2 Catalysts for Selective Olefin Hydrogenation under Ambient Conditions

The need to develop green and cost-effective industrial catalytic processes has led to growing interest in preparing more robust, efficient, and selective heterogeneous catalysts at a large scale. In this regard, microwave-assisted synthesis is a fast method for fabricating heterogeneous catalysts (including metal oxides, zeolites, metal-organic frameworks, and supported metal nanoparticles) with enhanced catalytic properties, enabling synthesis scale-up. Herein, the synthesis of nanosized UiO-66-NH2 was optimized via a microwave-assisted hydrothermal method to obtain defective matrices essential for the stabilization of metal nanoparticles, promoting catalytically active sites for hydrogenation reactions (760 kg·m-3·day-1 space time yield, STY). Then, this protocol was scaled up in a multimodal microwave reactor, reaching 86% yield (ca. 1 g, 1450 kg·m-3·day-1 STY) in only 30 min. Afterward, Pd nanoparticles were formed in situ decorating the nanoMOF by an effective and fast microwave-assisted hydrothermal method, resulting in the formation of Pd@UiO-66-NH2 composites. Both the localization and oxidation states of Pd nanoparticles (NPs) in the MOF were achieved using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), respectively. The optimal composite, loaded with 1.7 wt % Pd, exhibited an extraordinary catalytic activity (>95% yield, 100% selectivity) under mild conditions (1 bar H2, 25 °C, 1 h reaction time), not only in the selective hydrogenation of a variety of single alkenes (1-hexene, 1-octene, 1-tridecene, cyclohexene, and tetraphenyl ethylene) but also in the conversion of a complex mixture of alkenes (i.e., 1-hexene, 1-tridecene, and anethole). The results showed a powerful interaction and synergy between the active phase (Pd NPs) and the catalytic porous scaffold (UiO-66-NH2), which are essential for the selectivity and recyclability.

Adsorption and activation of small molecules on boron nitride catalysts

Hexagonal boron nitride possesses a unique layered structure, high specific surface area and similar electronic properties as graphene, which makes it not only a promising catalyst support, but also a highly effective metal-free catalyst in the booming field of green chemistry. Reactions involving small molecules (e.g., oxygen, low carbon alkanes, nitrogen and carbon dioxide) have always been a hot topic in catalytic research, especially associated with the adsorption and activation regime of different forms of small molecules on catalysts. In this review, we have investigated the adsorption of different small molecules and the relevant activation mechanisms of four typical chemical bonds (OO, C-H, NN, CO) on hexagonal boron nitride. Recent progress on approaches adopted to enhance the activation capacity such as doping, defect engineering and heterostructuring are summarized, highlighting the potential applications of nonmetallic hexagonal boron nitride catalysts in various reactions. This comprehensive investigation offers a reference point for the enhanced mechanistic understanding and future design of effective and sustainable catalytic systems based on boron nitride.

Advances and Challenges in Development of Transition Metal Catalysts for Heterogeneous Hydrogenation of Organic Compounds

Actual problems of development of catalysts for hydrogenation of heterocyclic compounds by hydrogen are summarized and discussed. The scope of review covers composites of nanoparticles of platinum group metals and 3d metals for heterogeneous catalytic processes. Such problems include increase of catalyst activity, which is important for reduction of precious metals content; development of new catalytic systems which do not contain metals of platinum group or contain cheaper analogues of Pd; control of factors which make influence on the selectivity of the catalysts; achievement of high reproducibility of the catalyst's performance and quality control of the catalysts. Own results of the authors are also summarized and described. The catalysts were prepared by decomposition of Pd0 and Ni0 complexes, pyrolysis of Ni2+ and Co2+ complexes deposited on aerosil and reduction of Ni2+ in pores of porous support in situ. The developed catalysts were used for hydrogenation of multigram batches of heterocyclic compounds.