Boosting Creation of Oxygen Vacancies in Co-Co3O4 Homogeneous Hybrids for Aerobic Oxidation of Cyclohexane

Fabrication of Fe-Zr, Co-Zr, and Ni-Zr Catalysts to Boost CNTs Synthesis from Plastic Wastes and the Electrocatalytic Oxygen Evolution Reaction

The efficient conversion of plastic wastes to high-value carbon materials like carbon nanotubes (CNTs) is one important issue about the rational recycling, reduction, and reuse of solid wastes. Herein, Fe-, Co-, and Ni-Zr catalysts were prepared and used for CNTs synthesis from polyethylene (PE) waste via a two-stage reaction system. At the same time, the effects of the PE/catalyst ratio and reaction temperature on CNTs synthesis have been studied. Compared with Co-Zr and Ni-Zr, Fe-Zr exhibited the best activity in CNTs synthesis from PE, and it achieved the highest CNTs yield of 806.3 mg/g (per gram of Fe-Zr) at 800 °C with a PE/catalyst ratio of 4. Furthermore, the obtained Fe-Zr/CNTs composite exhibited a low overpotential of 267 mV for the electrocatalytic oxygen evolution reaction (OER) at 20 mA/cm2 in 1 M KOH electrolyte solution, which was 21 mV lower than commercial RuO2 (288 mV) and 50 mV lower than Fe-Zr (317 mV). It was deduced that the in situ growth of CNTs reduced the charge transfer resistance and improved the electron transport efficiency of the Fe-Zr/CNTs composite, leading to superior activity in the electrocatalytic OER. This work provided detailed information for the preparation of the metal/CNTs composite from plastic wastes, which contributed positively to alleviate the environment and energy crisis.

Constructing a Pd-Co Interface to Tailor a d-Band Center for Highly Efficient Hydroconversion of Furfural over Cobalt Oxide-Supported Pd Catalysts

Cobalt is an alternative catalyst for furfural hydrogenation but suffers from the strong binding of H and furan ring on the surface, resulting in low catalytic activity and chemoselectivity. Herein, by constructing a Pd-Co interface in cobalt oxide-supported Pd catalysts to tailor the d-band center of Co, the concerted effort of Pd and Co boosts the catalytic performance for the hydroconversion of furfural to cyclopentanone and cyclopentanol. The increased dispersion of Pd on acid etching Co3O4 promotes the reduction of Co3+ to Co0 by enhancing hydrogen spillover, favoring the creation of the Pd-Co interface. Both experimental and theoretical calculations demonstrate that the electron transfer from Pd to Co at the interface results in the downshift of the d-band center of Co atoms, accompanied by the destabilization of H and furan ring adsorption on the Co surface, respectively. The former improves the furfural hydrogenation with TOF on Co elevating from 0.20 to 0.62 s-1, and the latter facilitates the desorption of formed furfuryl alcohol from the Co surface for subsequently hydrogenative rearrangement of the furan ring to cyclopentanone on acid sites. The resultant Pd/Co3O4-6 catalyst delivers superior activity with a 99% furfural conversion and 85% overall selectivity toward cyclopentanone/cyclopentanol. We anticipate that such a concept of tailoring the d-band center of Co via interface engineering provides novel insight and feasible approach for the design of highly efficient catalysts for furfural hydroconversion and beyond.

Efficient and Selective Oxygenation of Cycloalkanes and Alkyl Aromatics with Oxygen through Synergistic Catalysis of Bimetallic Active Centers in Two-Dimensional Metal-Organic Frameworks Based on Metalloporphyrins

Confined catalytic realms and synergistic catalysis sites were constructed using bimetallic active centers in two-dimensional metal-organic frameworks (MOFs) to achieve highly selective oxygenation of cycloalkanes and alkyl aromatics with oxygen towards partly oxygenated products. Every necessary characterization was carried out for all the two-dimensional MOFs. The selective oxygenation of cycloalkanes and alkyl aromatics with oxygen was accomplished with exceptional catalytic performance using two-dimensional MOF Co-TCPPNi as a catalyst. Employing Co-TCPPNi as a catalyst, both the conversion and selectivity were improved for all the hydrocarbons investigated. Less disordered autoxidation at mild conditions, inhibited free-radical diffusion by confined catalytic realms, and synergistic C-H bond oxygenation catalyzed by second metal center Ni employing oxygenation intermediate R-OOH as oxidant were the factors for the satisfying result of Co-TCPPNi as a catalyst. When homogeneous metalloporphyrin T(4-COOCH3)PPCo was replaced by Co-TCPPNi, the conversion in cyclohexane oxygenation was enhanced from 4.4% to 5.6%, and the selectivity of partly oxygenated products increased from 85.4% to 92.9%. The synergistic catalytic mechanisms were studied using EPR research, and a catalysis model was obtained for the oxygenation of C-H bonds with O2. This research offered a novel and essential reference for both the efficient and selective oxygenation of C-H bonds and other key chemical reactions involving free radicals.