Qihao Yang

Polydimethylsiloxane Coating for a Palladium/MOF Composite: Highly Improved Catalytic Performance by Surface Hydrophobization

Surface wettability of active sites plays a crucial role in the activity and selectivity of catalysts. This report describes modification of surface hydrophobicity of Pd/UiO-66, a composite comprising a metal-organic framework (MOF) and stabilized palladium nanoparticles (NPs), using a simple polydimethylsiloxane (PDMS) coating. The modified catalyst demonstrated significantly improved catalytic efficiency. The approach can be extended to various Pd nanoparticulate catalysts for enhanced activity in reactions involving hydrophobic reactants, as the hydrophobic surface facilitates the enrichment of hydrophobic substrates around the catalytic site. PDMS encapsulation of Pd NPs prevents aggregation of NPs and thus results in superior catalytic recyclability. Additionally, PDMS coating is applicable to a diverse range of catalysts, endowing them with additional selectivity in sieving reactants with different wettability.

Hollow Metal–Organic Framework Nanospheres via Emulsion-Based Interfacial Synthesis and Their Application in Size-Selective Catalysis

Metal-organic frameworks (MOFs) represent an emerging class of crystalline materials with well-defined pore structures and hold great potentials in a wide range of important applications. The functionality of MOFs can be further extended by integration with other functional materials, e.g., encapsulating metal nanoparticles, to form hybrid materials with novel properties. In spite of various synthetic approaches that have been developed recently, a facile method to prepare hierarchical hollow MOF nanostructures still remains a challenge. Here we describe a facile emulsion-based interfacial reaction method for the large-scale synthesis of hollow zeolitic imidazolate framework 8 (ZIF-8) nanospheres with controllable shell thickness. We further demonstrate that functional metal nanoparticles such as Pd nanocubes can be encapsulated during the emulsification process and used for heterogeneous catalysis. The inherently porous structure of ZIF-8 shells enables encapsulated catalysts to show size-selective hydrogenation reactions.

A seed-mediated approach to the general and mild synthesis of non-noble metal nanoparticles stabilized by a metal–organic framework for highly efficient catalysis

A novel and facile in situ seed-mediated synthetic approach has been developed to reduce non-noble metal precursors (Ni2+, Co2+, Fe2+, etc.) at room temperature, by taking advantage of a trace amount of noble metal cations (Ag+, Pd2+, Pt2+, Au3+, etc.) as a seed/initiator and NH3BH3 as a moderate reducing agent. The obtained noble metal-seed-mediated (NMSM) non-noble metal nanoparticles (NPs), stabilized by a metal–organic framework, are low-cost and display superior catalytic activity in the hydrolytic dehydrogenation of NH3BH3 under ambient conditions. As a representative catalyst, Ag-doped Ni/MIL-101 (with a Ag/Ni molar ratio as low as 1/200), exhibited a much higher activity than any of the other corresponding counterparts.

Encapsulating surface-clean metal nanoparticles inside metal–organic frameworks for enhanced catalysis using a novel γ-ray radiation approach

A facile and efficient γ-radiation strategy has been developed to incorporate surface-clean metal nanoparticles (NPs) into UiO-66-NH2 in the absence of stabilizing agents and additional reductants. This approach is enabled by metal ion reduction with active e−aq and H˙ species derived from water radiolysis. As a result, highly dispersed Pd NPs with narrow size distribution were generated and evenly dispersed in UiO-66-NH2. More importantly, the radiation-reduced Pd NPs exhibit significantly enhanced catalytic activity and stability in olefin hydrogenation. Meanwhile, they are also highly active in the catalytic reduction of 4-nitrophenol to 4-aminophenol. Furthermore, the proposed radiation methodology could be successfully extended to prepare other metal NPs such as Au and Pt. Considering that γ-ray radiation is widely used in industry, this study provides a potentially scalable approach to incorporate metallic nanomaterials into metal–organic frameworks with improved catalytic performance.