Polyolefins, the largest used commodity plastics in the world, find extensive application in many fields. However, most end up in landfills or incineration, leading to severe ecological crises, environmental pollution, and serious resource waste problems. As representatives on chemical upcycling of polyolefin plastics polyolefin waste to fuels and bulk/fine chemicals, polyolefin catalytic cracking and hydrocracking based on zeolite or metal/zeolite composite catalysts are considered the most effective paths due to their large capacity and strong adaptability to existing petrochemical equipment. After an overview of the reaction mechanisms of pyrolysis and catalytic cracking, this review aims to comprehensively discuss the influence of zeolite catalyst structure (acidity, pore structure, and morphology) on the catalytic activity, selectivity, and stability of polyolefin cracking, particularly emphasizing the importance for matching acidity and pore structure for target product formation. Subsequently, the structure–activity relationship between the metal site and zeolite’s acid site in polyolefin hydrocracking is also discussed. In the end, emerging opportunities and challenges are proposed to promote a more efficient way for polyolefin chemical upcycling. 

Understanding the Structure–Activity Relationships in Catalytic Conversion of Polyolefin Plastics by Zeolite-Based Catalysts: A Critical Review

Co/N-doped carbon nanospheres derived from an adenine-based metal organic framework enabled high-efficiency electrocatalytic nitrate reduction to ammonia.

Heterojunction materials are promising candidates for oxygen evolution reaction (OER) electrocatalysts to break the linear scaling relationship and lower the reaction barrier. However, the application of heterojunction materials is always hindered by the complicated multistep synthetic procedures which bring cost, complexity, and reproducibility issues. Herein, a strategy of kinetic controlled synthesis is developed to achieve the one‐pot formation of bimetallic metal‐organic framework (MOF)/layered double hydroxide (LDH) heterojunction electrodes as highly efficient OER electrocatalysts. The heterojunction electrodes present hierarchical structures with highly porous NiFe‐LDH nanosheet networks vertically grown on the surface of NiFe‐MOF‐74 microprisms, promoting fast mass transport and high exposure of active sites. The strong interactions at the MOF/LDH heterojunction interfaces contribute to the outstanding OER activity surpassing the state‐of‐art RuO2 OER catalysts. The MOF/LDH heterojunction electrode exhibits an ultralow overpotential of only 159.7 mV to reach the current density of 10 mA cm−2, and yields large current densities at small overpotential (100 mA cm−2 at 230.2 mV and 1000 mA cm−2 at 284.3 mV) with long‐term durability. This study presents an innovative approach to construct heterojunction materials with simple one‐step synthesis, offering a promising pathway for high‐efficiency electrocatalyst development.

A Kinetic Control Strategy for One‐Pot Synthesis of Efficient Bimetallic Metal‐Organic Framework/Layered Double Hydroxide Heterojunction Oxygen Evolution Electrocatalysts

The volcano-shaped relationship is very common in electrocatalytic nitrogen reduction reaction (e-NRR) and is usually caused by the competition between the first and last hydrogenation steps. How to break such a relationship to further improve the catalytic performance remains a great challenge. Herein, using first-principles calculations, we investigate a range of transition-metal (TM)-doped Cu-based single-atom alloys (TM1-Cu(111)) as catalysts for e-NRR. When the adsorption of N2 on the catalysts is strong enough, the inert N2 molecules can be effectively activated for the first hydrogenation step. Meanwhile, the last hydrogenation step is not affected by the scaling relationship and remains easy on all of the catalysts due to the unstable top-site adsorption of NH2, resulting in the break of the volcano-shaped relationship in e-NRR. Thus, only the first hydrogenation step is identified as the potential determining step. Four TM1-Cu(111) catalysts (TM = Re, W, Tc, and Mo) are selected as promising catalysts with limiting potential ranging from -0.38 to -0.56 V, showing outstanding e-NRR activity. Besides, the four catalysts also inhibit the competing hydrogen evolution reaction and long-term stability. Our work provides a guideline for breaking the volcano-shaped relationship in e-NRR and significant in the rational design of highly efficient electrocatalysts.

Breaking the Volcano-Shaped Relationship for Highly Efficient Electrocatalytic Nitrogen Reduction: A Computational Guideline.

Design of novel transition-metal-doped C4N4 as highly effective electrocatalysts for nitrogen fixation with a new intrinsic descriptor

The recently emerged single-atom alloy (SAA) catalysts have assembled the merits of the single atom catalysts (SACs) and the alloy catalysts, showing a great potential for driving nitrogen reduction reaction...

ʺSabatier principleʺ of d electron number for describing the nitrogen reduction reaction performance on single-atom alloy catalysts

Reducing the usage of Pt for oxygen reduction reaction (ORR) is of great significance for the commercialization of proton exchange membrane fuel cells. Herein, triple-junction interface of Pt-CeO2-nitrogen doped carbon...

Well-controlled Pt-CeO2-nitrogen doped carbon triple-junction catalysts with enhanced activity and durability for oxygen reduction reaction

The development of catalysts for electrochemical nitrogen reduction toward ammonia: theoretical and experimental advances.

Electrochemical reduction of nitrate to ammonia (NH3 ) not only offers a promising strategy for green NH3 synthesis, but also addresses the environmental issues and balances the perturbed nitrogen cycle. However, current electrocatalytic nitrate reduction processes are still inefficient due to the lack of effective electrocatalysts. Here 3D nanoporous Cu/MnOx hybrids are reported as efficient and durable electrocatalysts for nitrate reduction reaction, achieving the NH3 yield rates of 5.53 and 29.3 mg h-1 mgcat. -1 with 98.2% and 86.2% Faradic efficiency in 0.1 m Na2 SO4 solution with 10 and 100 mm KNO3 , respectively, which are higher than those obtained for most of the reported catalysts under similar conditions. Both the experimental results and density functional theory calculations reveal that the interface effect between Cu/MnOx interface could reduce the free energy of rate determining step and suppress the hydrogen evolution reaction, leading to the enhanced catalytic activity and selectivity. This work provides an approach to design advanced materials for NH3 production via electrochemical nitrate reduction.

Interfacially Engineered Nanoporous Cu/MnOx Hybrids for Highly Efficient Electrochemical Ammonia Synthesis via Nitrate Reduction.

Surface metal hydrides (M-H) are ubiquitous in heterogeneous catalytic reactions, while the detailed characterizations are frequently hindered by their high reactivity/low concentration, and the complicated surface structures of the host solids, especially in terms of practical solid catalysts. Herein, combining instant quenching capture and advanced solid-state NMR methodology, we report the first direct and unambiguous NMR evidence on the highly reactive surface gallium hydrides (Ga-H) over a practical Ga2O3 catalyst during direct H2 activation. The spectroscopic effects of 69Ga and 71Ga isotopes on the 1H NMR signal are clearly differentiated and clarified, allowing a concrete discrimination of the Ga-H signal from the hydroxyl crowd. Accompanied with quantitative and two-dimensional NMR spectroscopical methods, as well as density functional theory calculations, information on the site specification, structural configuration, and formation mechanism of the Ga-H species has been revealed, along with the H2 dissociation mechanism. More importantly, the successful spectroscopic identification and isolation of the surface Ga-H allow us to clearly reveal the critical but ubiquitous intermediate role of this species in catalytic reactions, such as propane dehydrogenation and CO2 hydrogenation reactions. The analytic approach presented in this work can be extended to other M-H analysis, and the insights will benefit the design of more efficient Ga-based catalysts.

Zhili Wang

Papers

ʺSabatier principleʺ of d electron number for describing the nitrogen reduction reaction performance on single-atom alloy catalysts

Well-controlled Pt-CeO2-nitrogen doped carbon triple-junction catalysts with enhanced activity and durability for oxygen reduction reaction

The development of catalysts for electrochemical nitrogen reduction toward ammonia: theoretical and experimental advances.

Interfacially Engineered Nanoporous Cu/MnOx Hybrids for Highly Efficient Electrochemical Ammonia Synthesis via Nitrate Reduction.

Direct Detection of Reactive Gallium-Hydride Species on the Ga2O3 Surface via Solid-State NMR Spectroscopy.