Retrofitting Zr-Oxo Nodes of UiO-66 by Ru Single Atoms to Boost Methane Hydroxylation with Nearly Total Selectivity.

Direct selective oxidation of methane (DSOM) to high value-added oxygenates under mild conditions is attracting considerable interest. Although state-of-the-art supported metal catalysts can improve methane conversion, it is still challenging to avoid the deep oxidation of oxygenates. Here, we develop a highly efficient metal-organic frameworks (MOFs)-supported single-atom Ru catalyst (Ru1/UiO-66) for the DSOM reaction using H2O2 as an oxidant. It endows nearly 100% selectivity and an excellent turnover frequency of 185.4 h-1 for the production of oxygenates. The yield of oxygenates is an order of magnitude higher than that on UiO-66 alone and several times higher than that on supported Ru nanoparticles or other conventional Ru1 catalysts, which show severe CO2 formation. Detailed characterizations and density functional theory calculations reveal a synergistic effect between the electron-deficient Ru1 site and the electron-rich Zr-oxo nodes of UiO-66 on Ru1/UiO-66. The Ru1 site is responsible for the activation of CH4 via the resulting Ru1═O* species, while the Zr-oxo nodes undertake the formation of oxygenic radical species to produce oxygenates. In particular, the Zr-oxo nodes retrofitted by Ru1 can prune the excess H2O2 to inactive O2 more than •OH species, helping to suppress the over-oxidation of oxygenates.

Zirconium-oxo Nodes of MOFs with Tunable Electronic Properties Provide Effective ⋠OH Species for Enhanced Methane Hydroxylation.

Direct conversion of methane to high value-added oxygenates under mild conditions has attracted extensive interest. However, the over-oxidation of target products is usually unavoidable due to the easily excessive activation of C-H bond on the sites of supported metal species. Here, we identified the most efficient Zr-oxo nodes of UiO-66 metal-organic frameworks (MOFs) catalysts for the selective oxidation of methane with H2 O2 . These nodes were modified by three types of benzene 1, 4-dicarboxylates (NH2 -BDC, H2 BDC, and NO2 -BDC). Detailed characterizations and DFT calculations revealed that these ligands can effectively tune the electronic properties of Zr-oxo nodes and the H2 BDC ligand led to optimal electronic density of Zr-oxo nodes in UiO-66. Thus the UiO-66-H catalyst promoted the formation of ⋅OH species that adsorbed on Zr-oxo nodes, and facilitated the activation of methane with a lower energy barrier and subsequent conversion to hydroxylation oxygenates with 100 % selectivity.

In Situ Transformation of ZIF-8 into Porous Overlayer on Ru/ZnO for Enhanced Hydrogenation Catalysis.

Supported metal catalysts play a significant role in heterogeneous catalysis in liquid phase reaction systems, but they usually suffer from a stability problem. Encapsulation of active metal species without the compromise of catalytic performance has been considered as an effective strategy. Here, we report an ultrastable Ru-based catalyst with particle size of around 1.1 nm for selective hydrogenation reaction. The highly dispersed Ru species are covered by the in situ formed porous N-C-ZnO overlayer, which is induced through the transforming of ZIF-8 shell that derives from a ZnO substrate. The resulting Ru/ZnO@N-C-ZnO catalyst can exhibit good stability in the hydrogenation of p-chloronitrobenzene after 20 cyclic runs with 100% selectivity toward p-chloroaniline. Comparatively, the naked Ru/ZnO catalyst with larger Ru particles shows serious metal leaching issue with inferior stability and poor selectivity. It is revealed that the excellent performance of Ru/ZnO@N-C-ZnO is attributed to the porous overlayer, which strengthens the bonding of Ru nanoparticles on ZnO.

Catalytic Upgrading of Ethanol to n-Butanol: Progress in Catalyst Development.

Because n-butanol as a fuel additive has more advantageous physicochemical properties than those of ethanol, ethanol valorization to n-butanol through homo- or heterogeneous catalysis has received much attention in recent decades in both scientific and industrial fields. Recent progress in catalyst development for upgrading ethanol to n-butanol, which involves homogeneous catalysts, such as iridium and ruthenium complexes, and heterogeneous catalysts, including metal oxides, hydroxyapatite (HAP), and, in particular, supported metal catalysts, is reviewed herein. The structure-activity relationships of catalysts and underlying reaction mechanisms are critically examined, and future research directions on the design and improvement of catalysts are also proposed.