Bifunctional zeolites-silver catalyst enabled tandem oxidation of formaldehyde at low temperatures

Graphitized Carbon-Supported Co@Co3O4 for Ozone Decomposition over the Entire Humidity Range

Ground-level ozone (O3) pollution has emerged as a significant concern due to its detrimental effects on human health and the ecosystem. Catalytic removal of O3 has proven to be the most efficient and cost-effective method. However, its practical application faces substantial challenges, particularly in relation to its effectiveness across the entire humidity range. Herein, we proposed a novel strategy termed "dual active sites" by employing graphitized carbon-loaded core-shell cobalt catalysts (Co@Co3O4-C). Co@Co3O4-C was synthesized via the pyrolysis of a Co-organic ligand as the precursor. By utilizing this approach, we achieved a nearly constant 100% working efficiency of the Co@Co3O4-C catalyst for catalyzing O3 decomposition across the entire humidity range. Physicochemical characterization coupled with density functional theory calculations elucidates that the presence of encapsulated metallic Co nanoparticles enhances the reactivity of the cobalt oxide capping layer. Additionally, the interface carbon atom, strongly influenced by adjacent metallic Co nuclei, functions as a secondary active site for the decomposition of O3 decomposition. The utilization of dual active sites effectively mitigates the competitive adsorption of H2O molecules, thus isolating them for adsorption in the cobalt oxide capping layer. This optimized configuration allows for the decomposition of O3 without interference from moisture. Furthermore, O3 decomposition monolithic catalysts were synthesized using a material extrusion-based three-dimensional (3D) printing technology, which demonstrated a low pressure drop and exceptional mechanical strength. This work provides a "dual active site" strategy for the O3 decomposition reaction, realizing O3 catalytic decomposition over the entire humidity range.

Unveiling the Role of Water in Heterogeneous Photocatalysis of Methanol Conversion for Efficient Hydrogen Production

Water molecules, which act as both solvent and reactant, play critical roles in photocatalytic reactions for methanol conversion. However, the influence of water on the adsorption of methanol and desorption of liquid products, which are two essential steps that control the performance in photocatalysis, has been well under-explored. Herein, we reveal the role of water in heterogeneous photocatalytic processes of methanol conversion on the platinized carbon nitride (Pt/C3N4) model photocatalyst. In situ spectroscopy techniques, isotope effects, and computational calculations demonstrate that water shows adverse effects on the adsorption of methanol molecules and desorption processes of methanol oxidation products on the surface of Pt/C3N4, significantly altering the reaction pathways in photocatalytic methanol conversion process. Guided by these discoveries, a photothermal-assisted photocatalytic system is designed to achieve a high solar-to-hydrogen (STH) conversion efficiency of 2.3 %, which is among the highest values reported. This work highlights the important roles of solvents in controlling the adsorption/desorption behaviours of liquid-phase heterogeneous catalysis.

Cooperative and Bifunctional Adsorbent-Catalyst Materials for In-situ VOCs Capture-Conversion

Volatile organic compounds (VOCs) are gases that are emitted into the air from products or processes and are major components of air pollution that significantly deteriorate air quality and seriously affect human health. Different types of metals, metal oxides, mixed-metal oxides, polymers, activated carbons, zeolites, metal-organic frameworks (MOFs) and mixed-matrixed materials have been developed and used as adsorbent or catalyst for diversified VOCs detection, removal, and destruction. In this comprehensive review, we first discuss the general classification of VOCs removal materials and processes and outline the historical development of bifunctional and cooperative adsorbent-catalyst materials for the removal of VOCs from air. Subsequently, particular attention is devoted to design of strategies for cooperative adsorbent-catalyst materials, along with detailed discussions on the latest advances on these bifunctional materials, reaction mechanisms, long-term stability, and regeneration for VOCs removal processes. Finally, challenges and future opportunities for the environmental implementation of these bifunctional materials are identified and outlined with the intent of providing insightful guidance on the design and fabrication of more efficient materials and systems for VOCs removal in the future.

Subnanometric Osmium Clusters Confined on Palladium Metallenes for Enhanced Hydrogen Evolution and Oxygen Reduction Catalysis

Highly efficient, cost-effective, and durable electrocatalysts, capable of accelerating sluggish reaction kinetics and attaining high performance, are essential for developing sustainable energy technologies but remain a great challenge. Here, we leverage a facile heterostructure design strategy to construct atomically thin Os@Pd metallenes, with atomic-scale Os nanoclusters of varying geometries confined on the surface layer of the Pd lattice, which exhibit excellent bifunctional properties for catalyzing both hydrogen evolution (HER) and oxygen reduction reactions (ORR). Importantly, Os5%@Pd metallenes manifest a low η10 overpotential of only 11 mV in 1.0 M KOH electrolyte (HER) as well as a highly positive E1/2 potential of 0.92 V in 0.1 M KOH (ORR), along with superior mass activities and electrochemical durability. Theoretical investigations reveal that the strong electron redistribution between Os and Pd elements renders a precise fine-tuning of respective d-band centers, thereby guiding adsorption of hydrogen and oxygen intermediates with an appropriate binding energy for the optimal HER and ORR.

Formaldehyde Ambient-Temperature Decomposition over Pd/Mn3O4-MnO Driven by Active Sites' Self-Tandem Catalysis

The widespread presence of formaldehyde (HCHO) pollutant has aroused significant environmental and health concerns. The catalytic oxidation of HCHO into CO2 and H2O at ambient temperature is regarded as one of the most efficacious and environmentally friendly approaches; to achieve this, however, accelerating the intermediate formate species formation and decomposition remains an ongoing obstacle. Herein, a unique tandem catalytic system with outstanding performance in low-temperature HCHO oxidation is proposed on well-structured Pd/Mn3O4-MnO catalysts possessing bifunctional catalytic centers. Notably, the optimized tandem catalyst achieves complete oxidation of 100 ppm of HCHO at just 18 °C, much better than the Pd/Mn3O4 (30%) and Pd/MnO (27%) counterparts as well as other physical tandem catalysts. The operando analyses and physical tandem investigations reveal that HCHO is primarily activated to gaseous HCOOH on the surface of Pd/Mn3O4 and subsequently converted to H2CO3 on the Pd/MnO component for deep decomposition. Theoretical studies disclose that Pd/Mn3O4 exhibits a favorable reaction energy barrier for the HCHO → HCOOH step compared to Pd/MnO; while conversely, the HCOOH → H2CO3 step is more facilely accomplished over Pd/MnO. Furthermore, the nanoscale intimacy between two components enhances the mobility of lattice oxygen, thereby facilitating interfacial reconstruction and promoting interaction between active sites of Pd/Mn3O4 and Pd/MnO in local vicinity, which further benefits sustained HCHO tandem catalytic oxidation. The tandem catalysis demonstrated in this work provides a generalizable platform for the future design of well-defined functional catalysts for oxidation reactions.

Local Electron Environment Regulation of Spinel CoMn2O4 Induced Effective Reactant Adsorption and Transformation of Lattice Oxygen for Toluene Oxidation

In contrast to numerous studies on oxygen species, the interaction of volatile organic compounds (VOCs) with oxides is also critical to the catalytic reaction but has hardly been considered. Herein, we develop a highly efficient Pt atom doped spinel CoMn2O4 (Pt-CoMn) for oxidation of toluene at low temperature, and the toluene conversion rate increased by 18.3 times (129.7 versus 7.1 × 10-11 mol/(m2·s)) at 160 °C compared to that of CoMn2O4. Detailed characterizations and density functional theory calculations reveal that the local electron environment of the Co sites is changed after Pt doping, and the formed electron-deficient Co sites in turn strengthen the interaction with toluene. Adsorbed toluene will react with lattice oxygen in Pt-CoMn and CoMn catalysts and convert into benzoate intermediates, and the consumption rate of benzoate is closely related to the activation of gaseous oxygen. Significantly, the abundant bulk defects of Pt-CoMn help to open the reaction channel in the CoMn spinel, which acts as an oxygen pump to promote the transformation of bulk lattice oxygen into surface lattice oxygen at lower temperatures, thus accelerating the conversion rate of benzoate intermediates into CO2 and enhancing low-temperature combustion of toluene. Pt-CoMn developed here emphasizes the regulation of VOCs adsorption strength and lattice oxygen transformation processes on CoMn2O4 by adjusting the local electron environment, which will provide new guidance for the design of efficient oxide catalysts for catalytic oxidation.

Design of a SnO2/Zeolite Gas Sensor to Enhance Formaldehyde Sensing Properties: From the Strategy of the Band Gap-Tunable Zeolite

ZSM-5 zeolite is usually used in gas sensors as an auxiliary material to improve the gas-sensitive properties of other semiconductor materials, such as its molecular sieve properties and surface adsorption properties. Here, the gas-sensitive mechanism analysis of SnO2/zeolite gas sensors is studied for the first time based on the perspective of zeolite as a band gap-tunable semiconductor that was reported recently. The gas-sensing mechanism of the zeolite/semiconductor has been modeled based on the surface charge theory, and the work function of the ZSM-5 zeolite has been revealed for the first time. A heterostructure of Ag and ZSM-5 was designed and compounded to tune the band gap of the ZSM-5 zeolite by the ammonia pool effect method. The band gap width of the zeolite decreases from 4.51 to 3.61 eV. A series of characterization techniques were used to analyze the distribution and morphology of silver nanoparticles in zeolites and the variation of the ZSM-5 band gap. Then, SnO2/Ag@ZSM-5 sensors were fabricated, and the gas-sensing performances were measured. The gas-sensing results show that the SnO2/Ag@ZSM-5 sensor has an improved response to formaldehyde in particular compared to the SnO2 sensor. The response value of the SnO2/Ag@ZSM-5 sensor to 70 ppm formaldehyde reached 29.4, which is a 528% improvement compared to the SnO2 sensor. Additionally, the selectivity was greatly enhanced. This study provides a strategy for designing and developing higher-performance gas sensors.

Silver-Exchanged Zeolite Y Catalyzes a Selective Insertion of Carbenes into C-H and O-H Bonds

Commercially available zeolite Y modulates the catalytic activity and selectivity of ultrasmall silver species during the Buchner reaction and the carbene addition to methylene and hydroxyl bonds, by simply exchanging the counter cations of the zeolite framework. The zeolite acts as a macroligand to tune the silver catalytic site, enabling the use of this cheap and recyclable solid catalyst for the in situ formation of carbenes from diazoacetate and selective insertion in different C-H (i.e., cyclohexane) and C-O (i.e., water) bonds. The amount of catalyst in the reaction can be as low as ≤0.1 mol % silver. Besides, this reactivity allows deeply drying the HY zeolite framework by making the strongly adsorbed water molecules react with the in situ formed carbenes.

Intergrowth Zeolites, Synthesis, Characterization, and Catalysis

Microporous zeolites that can act as heterogeneous catalysts have continued to attract a great deal of academic and industrial interest, but current progress in their synthesis and application is restricted to single-phase zeolites, severely underestimating the potential of intergrowth frameworks. Compared with single-phase zeolites, intergrowth zeolites possess unique properties, such as different diffusion pathways and molecular confinement, or special crystalline pore environments for binding metal active sites. This review first focuses on the structural features and synthetic details of all the intergrowth zeolites, especially providing some insightful discussion of several potential frameworks. Subsequently, characterization methods for intergrowth zeolites are introduced, and highlighting fundamental features of these crystals. Then, the applications of intergrowth zeolites in several of the most active areas of catalysis are presented, including selective catalytic reduction of NOx by ammonia (NH3-SCR), methanol to olefins (MTO), petrochemicals and refining, fine chemicals production, and biomass conversion on Beta, and the relationship between structure and catalytic activity was profiled from the perspective of intergrowth grain boundary structure. Finally, the synthesis, characterization, and catalysis of intergrowth zeolites are summarized in a comprehensive discussion, and a brief outlook on the current challenges and future directions of intergrowth zeolites is indicated.

Tailoring Zeolite L-Supported-Cu Catalysts for CO2 Hydrogenation: Insights into the Mechanism of CH3OH and CO Formation

The utilization of Cu-based catalysts in CO2 conversion into valuable chemicals is of significant interest due to their potential in mitigating greenhouse gas emissions. However, the controllable design of Cu-based catalysts and the regulation of their mechanism remain challenging. In this study, a series of efficient Cu/L catalysts were prepared for this process, and the intrinsic influencing factors on the reaction routes were systematically revealed. Various techniques revealed that Cu particles in L-supported catalysts exhibited higher dispersion and formed Cu-O(OH)-K interfacial sites. However, with increasing Cu loading, the dispersion of Cu particles and the percentage of Cu-O(OH)-K interfaces decreased. Kinetic investigations revealed that the adsorption configuration and electronic structure of Cu species codetermined the reaction pathways and resulting selectivity. Cu/L catalysts possessing Cu-O(OH)-K interfaces and small particles demonstrated the preferential formation of formate species, promoting methanol formation. However, larger Cu particles generated carboxylate intermediates, resulting in higher CO selectivity..

Tunable Interfacial Electronic Pd-Si Interaction Boosts Catalysis via Accelerating O2 and H2O Activation

Engineering the interfacial structure between noble metals and oxides, particularly on the surface of non-reducible oxides, is a challenging yet promising approach to enhancing the performance of heterogeneous catalysts. The interface site can alter the electronic and d-band structure of the metal sites, facilitating the transition of energy levels between the reacting molecules and promoting the reaction to proceed in a favorable direction. Herein, we created an active Pd-Si interface with tunable electronic metal-support interaction (EMSI) by growing a thin permeable silica layer on a non-reducible oxide ZSM-5 surface (termed Pd@SiO₂/ZSM-5). Our experimental results, combined with density functional theory calculations, revealed that the Pd-Si active interface enhanced the charge transfer from deposited Si to Pd, generating an electron-enriched Pd surface, which significantly lowered the activation barriers for O₂ and H₂O. The resulting reactive oxygen species, including O₂ ^-, O₂ ^2-, and -OH, synergistically facilitated formaldehyde oxidation. Additionally, moderate electronic metal-support interaction can promote the catalytic cycle of Pd⁰ ⇆ Pd²⁺, which is favorable for the adsorption and activation of reactants. This study provides a promising strategy for the design of high-performance noble metal catalysts for practical applications.

Unveiling the Position Effect of Ce within Layered MnO2 to Prolong the Ambient Removal of Indoor HCHO

The position of Ce doping has a significant effect on ambient HCHO storage and catalytic oxidation on layered MnO₂. By associating structure and performance, it is unveiled that doping Ce into the in-layered lattice of MnO₂ is favorable to the generation of high-valence Mn cations, enhancing the oxidizing ability and capacity, but an opposite influence is displayed by interlayered Ce doping. From the aspect of energy minimization calculated by DFT, in-layered Ce doping is also recommended due to the decreased energies for molecule adsorption and oxygen vacancy formation. As a result, in-layered Ce-doped MnO₂ displays exceptional activity in catalyzing the deep oxidation of HCHO and a fourfold higher capacity of ambient HCHO storage than pristine MnO₂. The optimal oxide is combined with electromagnetic induction heating to complete the "storage-oxidation" cycle as a promising approach absolutely depending on non-noble oxides and household appliances to realize the long-acting removal of indoor HCHO at room temperature.

Role of formaldehyde in promoting aromatic selectivity during methanol conversion over gallium-modified zeolites

Gallium-modified HZSM-5 zeolites are known to increase aromatic selectivity in methanol conversion. However, there are still disputes about the exact active sites and the aromatic formation mechanisms over Ga-modified zeolites. In this work, in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) experiments were carried out to study the behaviors of intermediates and products during methanol conversion over Ga-modified HZSM-5. The increased formaldehyde (HCHO) yield over Ga-modified HZSM-5 was found to play a key role in the increase in aromatic yields. More HCHO was deemed to be generated from the direct dehydrogenation of methanol, and Ga₂O₃ in Ga-modified HZSM-5 was found to be the active phase. The larger increase in aromatic production over Ga-modified HZSM-5 after reduction‒oxidation treatment was found to be the result of redispersed Ga₂O₃ with smaller size generating a larger amount of HCHO. This study provides some new insights into the internal driving force for promoting the production of aromatics over Ga-modified HZSM-5.

Tuning the Micro-coordination Environment of Al in Dealumination Y Zeolite to Enhance Electron Transfer at the Cu-Mn Oxides Interface for Highly Efficient Catalytic Ozonation of Toluene at Low Temperatures

The development of stable, highly active, and inexpensive catalysts for the ozone catalytic oxidation of volatile organic compounds (VOCs) is challenging but of great significance. Herein, the micro-coordination environment of Al in commercial Y zeolite was regulated by a specific dealumination method and then the dealuminated Y zeolite was used as the support of Cu-Mn oxides. The optimized catalyst Cu-Mn/DY exhibited excellent performance with around 95% of toluene removal at 30 °C. Besides, the catalyst delivered satisfactory stability in both high-humidity conditions and long-term reactions, which is attributed to more active oxygen vacancies and acidic sites, especially the strong Lewis acid sites newly formed in the catalyst. The decrease in the electron cloud density around aluminum species enhanced electron transfer at the interface between Cu-Mn oxides. Moreover, extra-framework octahedrally coordinated Al in the support promoted the electronic metal-support interaction (EMSI). Compared with single Mn catalysts, the incorporation of the Cu component changed the degradation pathway of toluene. Benzoic acid, as the intermediate of toluene oxidation, can directly ring-open on Cu-doped catalysts rather than being further oxidized to other byproducts, which increased the rate of the catalytic reaction. This work provides a new insight and theoretical guidance into the rational design of efficient catalysts for the catalytic ozonation of VOCs.

Acid-Modified Sepiolite-Supported Pt (Noble Metal) Catalysts for HCHO Oxidation at Ambient Temperature

The critical need to enhance the quality of indoor air leads to the improvement of catalyst activity for the removal of formaldehyde. Sepiolite can be utilized in catalytic reactions for its unique structure, composition and high surface area. The adhesion between sepiolite fibers and the blocked microporous channel (by impurities) demands the activation of natural sepiolite through acid treatment. This treatment successfully produces acid-modified sepiolite Pt-supported samples. The impacts of different acid concentrations, Pt loading content and calcination temperature on catalytic activity for formaldehyde (HCHO) oxidation are studied. The catalytic activity of HCHO is characterized and evaluated by techniques including specific surface area, X-ray diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy and transmission electron microscopy. The results show the maximum specific area of sepiolite at the optimized 0.06 M acid concentration. Among all the prepared samples, the 0.02Pt/Sep catalyst calcined at 500 °C exhibits the highest catalytic activity for the oxidation of HCHO.

Water-induced gaseous formaldehyde decomposition using ruthenium organic crystalline particles

Novel ruthenium organic crystalline particles are prepared for providing two distinctive approaches for formaldehyde decomposition: catalytic oxidation or water-induced formaldehyde decomposition.