Mechanism of Methanol Decomposition over Single-Site Pt1/CeO2 Catalyst: A DRIFTS Study

Simultaneously Promoted Water Resistance and CO2 Selectivity in Methanol Oxidation Over Pd/CoOOH: Synergy of Co-OH and the Pd-Olatt-Co Interface

Catalytic purification of industrial oxygenated volatile organic compounds (OVOCs) is hindered by the presence of water vapor that attacks the active sites of conventional noble metal-based catalysts and the insufficient mineralization that leads to the generation of hazardous intermediates. Developing catalysts simultaneously with excellent water resistance and a high intermediate suppression ability is still a great challenge. Herein, we proposed a simple strategy to synthesize a Pd/CoOOH catalyst that contains abundant hydroxyl groups and lattice oxygen species, over which a negligible effect was observed on CH3OH conversion with 3 vol % water vapor, while a remarkable conversion reduction of 24% was observed over Pd/Co3O4. Moreover, the low-temperature CO2 selectivity over Pd/CoOOH is significantly enhanced in comparison with Pd/Co(OH)2. The high concentration of surface hydroxyl groups on Pd/CoOOH enhances the water resistance owing to the accelerated activation of H2O to generate Co-OH, which replaces the consumed hydroxyl and facilitates the quick dissociation of surface H2O through timely desorption. Additionally, the presence of Pd-Olatt-Co promotes electron transport from Co to Pd, leading to improved metal-support interactions and weakened metal-O bonds. This in turn enhances the catalyst's capacity to efficaciously convert intermediates. This study sheds new insights into designing multifunctional catalytic platforms for efficient industrial OVOC purification as well as other heterogeneous oxidation reactions.

Polyoxometalates-Mediated Selectivity in Pt Single-Atoms on Ceria for Environmental Catalysis

Optimizing the reactivity and selectivity of single-atom catalysts (SACs) remains a crucial yet challenging issue in heterogeneous catalysis. This study demonstrates selective catalysis facilitated by a polyoxometalates-mediated electronic interaction (PMEI) in a Pt single-atom catalyst supported on CeO2 modified with Keggin-type phosphotungstate acid (HPW), labeled as Pt1/CeO2-HPW. The PMEI effect originates from the unique arrangement of isolated Pt atoms and HPW clusters on the CeO2 support. Electrons are transferred from the ceria support to the electrophilic tungsten in HPW clusters, and subsequently, Pt atoms donate electrons to the now electron-deficient ceria. This phenomenon enhances the positive charge of Pt atoms, moderating O2 activation and limiting lattice oxygen mobility compared to the conventional Pt1/CeO2 catalyst. The resulting electronic structure of Pt combined with the strong and local acidic environment of HPW on Pt1/CeO2-HPW leads to improved efficiency and N2 selectivity in the degradation of NH3 and NO, as well as increased CO2 yield when inputting volatile organic compounds. This study sheds the light on the design of SACs with balanced reactivity and selectivity for environmental catalysis.

Hydrophobic TaOx Species Overlayer Tuning Light-Driven Methane Chlorination with Inorganic Chlorine

Halogenated methane serves as a universal platform molecule for building high-value chemicals. Utilizing sodium chloride solution for photocatalytic methane chlorination presents an environmentally friendly method for methane conversion. However, competing reactions in gas-solid-liquid systems leads to low efficiency and selectivity in photocatalytic methane chlorination. Here, an in situ method is employed to fabricate a hydrophobic layer of TaOx species on the surface of NaTaO3. Through in-situ XPS and XANES spectra analysis, it is determined that TaOx is a coordination unsaturated species. The TaOx species transforms the surface properties from the inherent hydrophilicity of NaTaO3 to the hydrophobicity of TaOx/NaTaO3, which enhances the accessibility of CH4 for adsorption and activation, and thus promotes the methane chlorination reaction within the gas-liquid-solid three-phase system. The optimized TaOx/NaTaO3 photocatalyst has a good durability for multiple cycles of methane chlorination reactions, yielding CH3Cl at a rate of 233 µmol g-1 h-1 with a selectivity of 83%. In contrast, pure NaTaO3 exhibits almost no activity toward CH3Cl formation, instead catalyzing the over-oxidation of CH4 into CO2. Notably, the activity of the optimized TaOx/NaTaO3 photocatalyst surpasses that of reported noble metal photocatalysts. This research offers an effective strategy for enhancing the selectivity of photocatalytic methane chlorination using inorganic chlorine ions.

Unveiling Highly Sensitive Active Site in Atomically Dispersed Gold Catalysts for Enhanced Ethanol Dehydrogenation

Developing a desirable ethanol dehydrogenation process necessitates a highly efficient and selective catalyst with low cost. Herein, we show that the "complex active site" consisting of atomically dispersed Au atoms with the neighboring oxygen vacancies (Vo) and undercoordinated cation on oxide supports can be prepared and display unique catalytic properties for ethanol dehydrogenation. The "complex active site" Au-Vo-Zr3+ on Au1/ZrO2 exhibits the highest H2 production rate, with above 37,964 mol H2 per mol Au per hour (385 g H2 g Au - 1 ${{\rm{g}}_{{\rm{Au}}}^{ - 1} }$  h-1) at 350 °C, which is 3.32, 2.94 and 15.0 times higher than Au1/CeO2, Au1/TiO2, and Au1/Al2O3, respectively. Combining experimental and theoretical studies, we demonstrate the structural sensitivity of these complex sites by assessing their selectivity and activity in ethanol dehydrogenation. Our study sheds new light on the design and development of cost-effective and highly efficient catalysts for ethanol dehydrogenation. Fundamentally, atomic-level catalyst design by colocalizing catalytically active metal atoms forming a structure-sensitive "complex site", is a crucial way to advance from heterogeneous catalysis to molecular catalysis. Our study advanced the understanding of the structure sensitivity of the active site in atomically dispersed catalysts.

Imparting Chemiresistor with Humidity-Independent Sensitivity toward Trace-Level Formaldehyde via Substitutional Doping Platinum Single Atom

The modification of metal oxides with noble metals is one of the most effective means of improving gas-sensing performance of chemiresistors, but it is often accompanied by unintended side effects such as sensor resistance increases up to unmeasurable levels. Herein, a carbonization-oxidation method is demonstrated using ultrasonic spray pyrolysis technique to realize platinum (Pt) single atom (SA) substitutional doping into SnO2 (named PtSA-SnO2). The substitutional doping strategy can obviously enhance gas-sensing properties, and meanwhile decrease sensor resistance by two orders of magnitude (decreased from ≈850 to ≈2 MΩ), which are attributed to the tuning of band gap and fermi-level position, efficient single atom catalysis, and the raising of adsorption capability of formaldehyde, as validated by the state-of-the-art characterizations, such as spherical aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM), in situ diffuse reflectance infrared Fourier transformed spectra (in situ DRIFT), CO temperature-programmed reduction (CO-TPR), and theoretical calculations. As a proof of concept, the developed PtSA-SnO2 sensor shows humidity-independent (30-70% relative humidity) gas-sensing performance in the selective detection of formaldehyde with high response, distinguishable selectivity (8< Sformaldehyde/Sinterferant <14), and ultra-low detection limit (10 ppb). This work presents a generalized and facile method to design high-performance metal oxides for chemical sensing of volatile organic compounds (VOCs).

Tuning the Metal-Support Interaction by Modulating CeO2 Oxygen Vacancies to Enhance the Toluene Oxidation Activity of Pt/CeO2 Catalysts

In this research, a range of Pt/CeO2 catalysts featuring varying Pt-O-Ce bond contents were developed by modulating the oxygen vacancies of the CeO2 support for toluene abatement. The Pt/CeO2-HA catalyst generated a maximum quantity of Pt-O-Ce bonds (possessed the strongest metal-support interaction), as evidenced by the visible Raman results, which demonstrated outstanding toluene catalytic performance. Additionally, the UV Raman results revealed that the strong metal-support interaction stimulated a substantial increase in oxygen vacancies, which could facilitate the activation of gaseous oxygen to generate abundant reactive oxygen species accumulated on the Pt/CeO2-HA catalyst surface, a conclusion supported by the H2-TPR, XPS, and toluene-TPSR results. Furthermore, the results from quasi-in situ XPS, in situ DRIFTS, and DFT indicated that the Pt/CeO2-HA catalyst with a strong metal-support interaction led to improved mobility of reactive oxygen species and lower oxygen activation energies, which could transfer a large number of activated reactive oxygen species to the reaction interface to participate in the toluene oxidation, resulting in the relatively superior catalytic performance. The approach of tuning the metal-support interaction of catalysts offers a promising avenue to develop highly active catalysts for toluene degradation.

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.

Mechanistic Insight into Acceptorless Dehydrogenation of Methanol to Syngas Catalyzed by MACHO-Type Ruthenium and Manganese Complexes: A DFT Study

The acceptorless dehydrogenation of methanol to produce carbon monoxide (CO) and dihydrogen (H2) mediated by MACHO-type 1-Ru and 1-Mn complexes was theoretically investigated via density functional theory calculations. The 1-Ru-catalyzed process involves the formation of active species 4-Ru through a methanol-bridged H2 release pathway. Methanol dehydrogenation by 4-Ru yields formaldehyde and 1-Ru, followed by H2 release to regenerate 4-Ru (rate-determining step, ΔG‡ = 32.5 kcal/mol). Formaldehyde further reacts with methanol via nucleophilic attack of the MeO- ligand in the Ru complex (ΔG‡ = 9.6 kcal/mol), which is more favorable than the traditional methanol-to-formaldehyde nucleophilic attack (ΔG‡ = 33.8 kcal/mol) due to the higher nucleophilicity of MeO-. CO is ultimately produced through the methyl formate decarbonylation reaction. Accelerated H2 release in the early reaction stage compared to CO results from the initial methanol dehydrogenation and condensation of formaldehyde with methanol. In contrast, CO generation occurs later via methyl formate decarbonylation. The 1-Mn-catalyzed reaction has reduced efficiency compared to 1-Ru for the higher Gibbs energy barrier (ΔG‡ = 34.1 kcal/mol) of the rate-determining step. Excess NaOtBu promotes the reaction of CO and methanol, forming methyl formate, significantly reducing the CO/H2 ratio as the catalyst amount decreases. These findings deepen our understanding of the methanol-to-syngas transformation and can drive progress in this field.

Designing Cu0-Cu+ dual sites for improved C-H bond fracture towards methanol steam reforming

Copper-based catalysts serve as the predominant methanol steam reforming material although several fundamental issues remain ambiguous such as the identity of active center and the aspects of reaction mechanism. Herein, we prepare Cu/Cu(Al)Ox catalysts with amorphous alumina-stabilized Cu2O adjoining Cu nanoparticle to provide Cu0-Cu+ sites. The optimized catalyst exhibits 99.5% CH3OH conversion with a corresponding H2 production rate of 110.8 μmol s-1 gcat-1 with stability over 300 h at 240 °C. A binary function correlation between the CH3OH reaction rate and surface concentrations of Cu0 and Cu+ is established based on kinetic studies. Intrinsic active sites in the catalyst are investigated with in situ spectroscopy characterization and theoretical calculations. Namely, we find that important oxygen-containing intermediates (CH3O* and HCOO*) adsorb at Cu0-Cu+ sites with a moderate adsorption strength, which promotes electron transfer from the catalyst to surface species and significantly reduces the reaction barrier of the C-H bond cleavage in CH3O* and HCOO* intermediates.

Catalytic ozonation mechanism over M1-N3C1 active sites

The structure-activity relationship in catalytic ozonation remains unclear, hindering the understanding of activity origins. Here, we report activity trends in catalytic ozonation using a series of single-atom catalysts with well-defined M1-N3C1 (M: manganese, ferrum, cobalt, and nickel) active sites. The M1-N3C1 units induce locally polarized M - C bonds to capture ozone molecules onto M atoms and serve as electron shuttles for catalytic ozonation, exhibiting excellent catalytic activities (at least 527 times higher than commercial manganese dioxide). The combined in situ characterization and theoretical calculations reveal single metal atom-dependent catalytic activity, with surface atomic oxygen reactivity identified as a descriptor for the structure-activity relationship in catalytic ozonation. Additionally, the dissociation barrier of surface peroxide species is proposed as a descriptor for the structure-activity relationship in ozone decomposition. These findings provide guidelines for designing high-performance catalytic ozonation catalysts and enhance the atomic-level mechanistic understanding of the integral control of ozone and methyl mercaptan.

Improved Low-Temperature Hydrogen Production from Aqueous Methanol Based on Synergism between Cationic Pt and Interfacial Basic LaOx

Aqueous phase reforming of methanol (APRM) is simple, inexpensive and provides a high hydrogen gravimetric density of 18.8 wt. %, and so is superior to traditional gas-phase reactions performed at relatively high temperatures. In the present work, the interface between Pt nanoparticles and a TiN support was modified using a highly dispersed amorphous LaOx phase. The resulting Pt/LaOx /TiO(N) exhibited enhanced activity and long-term stability during the APRM reaction under base-free conditions compared with Pt catalysts supported on unmodified TiN or crystalline La2 O3 . The interfacial amorphous LaOx phase promoted the deposition of small Pt nanoparticles having a narrow size distribution, and also generated electron-deficient Pt. An assessment of kinetic isotope data and theoretical investigations demonstrated that the cationic Pt nanoparticles facilitated the cleavage of O-H and C-H bonds in methanol while the amorphous LaOx enhanced the dissociation of water, thus enabling the water-gas shift reaction under mild conditions.

Surface Engineering of TiO2 Nanosheets to Boost Photocatalytic Methanol Dehydrogenation for Hydrogen Evolution

Low-cost high-efficiency H₂ evolution is indispensable for its large-scale applications in the future. In the research, we expect to build high active photocatalysts for sunlight-driven H₂ production by surface engineering to adjust the work function of photocatalyst surfaces, adsorption/desorption ability of substrates and products, and reaction activation energy barrier. Single-atom Pt-doped TiO_2-x nanosheets (NSs), mainly including two facets of (001) and (101), with loading of Pt nanoparticles (NPs) at their edges (Pt/TiO_2-x-SAP) are successfully prepared by an oxygen vacancy-engaged synthetic strategy. According to the theoretical simulation, the implanted single-atom Pt can change the surface work function of TiO₂, which benefits electron transfer, and electrons tend to gather at Pt NPs adsorbed at (101) facet-related edges of TiO₂ NSs for H₂ evolution. Pt/TiO_2-x-SAP exhibits ultrahigh photocatalytic performance of hydrogen evolution from dry methanol with a quantum yield of 90.8% that is ∼1385 times higher than pure TiO_2-x NSs upon 365 nm light irradiation. The high H₂ generation rate (607 mmol g_cata^-1 h^-1) of Pt/TiO_2-x-SAP is the basis for its potential applications in the transportation field with irradiation of UV-visible light (100 mW cm^-2). Finally, lower adsorption energy for HCHO on Ti sites originated from TiO₂ (001) doping single-atom Pt is responsible for high selective dehydrogenation of methanol to HCHO, and H tends to favorably gather at Pt NPs on the TiO₂ (101) surface to produce H₂.

Genesis of Active Pt/CeO2 Catalyst for Dry Reforming of Methane by Reduction and Aggregation of Isolated Platinum Atoms into Clusters

Atomically dispersed metal catalysts offer the advantages of efficient metal utilization and high selectivities for reactions of technological importance. Such catalysts have been suggested to be strong candidates for dry reforming of methane (DRM), offering prospects of high selectivity for synthesis gas without coke formation, which requires ensembles of metal sites and is a challenge to overcome in DRM catalysis. However, investigations of the structures of isolated metal sites on metal oxide supports under DRM conditions are lacking, and the catalytically active sites remain undetermined. Data characterizing the DRM reaction-driven structural evolution of a cerium oxide-supported catalyst, initially incorporating atomically dispersed platinum, and the corresponding changes in catalyst performance are reported. X-ray absorption and infrared spectra show that the reduction and agglomeration of isolated cationic platinum atoms to form small platinum clusters/nanoparticles are necessary for DRM activity. Density functional theory calculations of the energy barriers for methane dissociation on atomically dispersed platinum and on platinum clusters support these observations. The results emphasize the need for in-operando experiments to assess the active sites in such catalysts. The inferences about the catalytically active species are suggested to pertain to a broad class of catalytic conversions involving the rate-limiting dissociation of light alkanes.

Ligand Assisted Thermal Atomization of Palladium Clusters: An Inspiring Approach for the Rational Design of Atomically Dispersed Metal Catalysts

The transformation from metal nanocluster catalysts to metal single-atom catalysts is an important procedure in the rational design of atomically dispersed metal catalysts (ADCs). However, the conversion methods often involve high annealing temperature as well as reducing atmosphere. Herein, we reported a continuous and convenient approach to transfer Pd nanocluster into Pd single-atom in a ligand assisted annealing procedure, by which means we reduced its activating temperature low to 400 °C. Using ex-situ microscopy and spectroscopy, we comprehensively monitored the structural evolution of Pd species though the whole atomization process. Theoretical calculation revealed that the structural instability caused by remaining Cl ligands was the main reason for this low-temperature transformation. The present atomization strategy and mechanistic knowledge for the conversion from cluster to atomic dispersion provides guidelines for the rational design of ADCs.

The Nature of Interfacial Catalysis over Pt/NiAl2O4 for Hydrogen Production from Methanol Reforming Reaction

Reforming of methanol is one of the most favorable chemical processes for on-board H₂ production, which alleviates the limitation of H₂ storage and transportation. The most important catalytic systems for methanol reacting with water are interfacial catalysts including metal/metal oxide and metal/carbide. Nevertheless, the assessment on the reaction mechanism and active sites of these interfacial catalysts are still controversial. In this work, by spectroscopic, kinetic, and isotopic investigations, we established a compact cascade reaction model (ca. the Langmuir-Hinshelwood model) to describe the methanol and water activation over Pt/NiAl₂O₄. We show here that reforming of methanol experiences methanol dehydrogenation followed by water-gas shift reaction (WGS), in which two separated kinetically relevant steps have been identified, that is, C-H bond rupture within methoxyl adsorbed on interface sites and O-H bond rupture within O_lH (O_l: oxygen-filled surface vacancy), respectively. In addition, these two reactions were primarily determined by the most abundant surface intermediates, which were methoxyl and CO species adsorbed on NiAl₂O₄ and Pt, respectively. More importantly, the excellent reaction performance benefits from the following bidirectional spillover of methoxyl and CO species since the interface and the vacancies on the support were considered as the real active component in methanol dehydrogenation and the WGS reaction, respectively. These findings provide deep insight into the reaction process as well as the active component during catalysis, which may guide the design of new catalytic systems.

Atom-Economical Synthesis of Dimethyl Carbonate from CO2 : Engineering Reactive Frustrated Lewis Pairs on Ceria with Vacancy Clusters

The chemical conversion of CO₂ to long-chain chemicals is considered as a highly attractive method to produce value-added organics, while the underlying reaction mechanism remains unclear. By constructing surface vacancy-cluster-mediated solid frustrated Lewis pairs (FLPs), the 100 % atom-economical, efficient chemical conversion of CO₂ to dimethyl carbonate (DMC) was realized. By taking CeO₂ as a model system, we illustrate that FLP sites can efficiently accelerate the coupling and conversion of key intermediates. As demonstrated, CeO₂ with rich FLP sites shows improved reaction activity and achieves a high yield of DMC up to 15.3 mmol g^-1 . In addition, by means of synchrotron radiation in situ diffuse reflectance infrared Fourier-transform spectroscopy, combined with density functional theory calculations, the reaction mechanism on the FLP site was investigated systematically and in-depth, providing pioneering insights into the underlying pathway for CO₂ chemical conversion to long-chain chemicals.

Sustainable production of hydrogen with high purity from methanol and water at low temperatures

Carbon neutrality initiative has stimulated the development of the sustainable methodologies for hydrogen generation and safe storage. Aqueous-phase reforming methanol and H2O (APRM) has attracted the particular interests for their high gravimetric density and easy availability. Thus, to efficiently release hydrogen and significantly suppress CO generation at low temperatures without any additives is the sustainable pursuit of APRM. Herein, we demonstrate that the dual-active sites of Pt single-atoms and frustrated Lewis pairs (FLPs) on porous nanorods of CeO2 enable the efficient additive-free H2 generation with a low CO (0.027%) through APRM at 120 °C. Mechanism investigations illustrate that the Pt single-atoms and Lewis acidic sites cooperatively promote the activation of methanol. With the help of a spontaneous water dissociation on FLPs, Pt single-atoms exhibit a significantly improved reforming of *CO to promote H2 production and suppress CO generation. This finding provides a promising path towards the flexible hydrogen utilizations.

CO2 Activation over Nanoshaped CeO2 Decorated with Nickel for Low-Temperature Methane Dry Reforming

Dry reforming of methane (DRM) is a promising way to convert methane and carbon dioxide into H₂ and CO (syngas). CeO₂ nanorods, nanocubes, and nanospheres were decorated with 1-4 wt % Ni. The materials were structurally characterized using TEM and in situ XANES/EXAFS. The CO₂ activation was analyzed by DFT and temperature-programmed techniques combined with MS-DRIFTS. Synthesized CeO₂ morphologies expose {111} and {100} terminating facets, varying the strength of the CO₂ interaction and redox properties, which influence the CO₂ activation. Temperature-programmed CO₂ DRIFTS analysis revealed that under hydrogen-lean conditions mono- and bidentate carbonates are hydrogenated to formate intermediates, which decompose to H₂O and CO. In excess hydrogen, methane is the preferred reaction product. The CeO₂ cubes favor the formation of a polydentate carbonate species, which is an inert spectator during DRM at 500 °C. Polydentate covers a considerable fraction of ceria's surface, resulting in less-abundant surface sites for CO₂ dissociation.

Insights into the Mechanism of Methanol Steam Reforming Tandem Reaction over CeO2 Supported Single-Site Catalysts

We demonstrated how the special synergy between a noble metal single site and neighboring oxygen vacancies provides an "ensemble reaction pool" for high hydrogen generation efficiency and carbon dioxide (CO₂) selectivity of a tandem reaction: methanol steam reforming. Specifically, the hydrogen generation rate over single site Ru₁/CeO₂ catalyst is up to 9360 mol H₂ per mol Ru per hour (579 mL_H2 g_Ru^-1 s^-1) with 99.5% CO₂ selectivity. Reaction mechanism study showed that the integration of metal single site and O vacancies facilitated the tandem reaction, which consisted of methanol dehydrogenation, water dissociation, and the subsequent water gas shift (WGS) reaction. In addition, the strength of CO adsorption and the reaction activation energy difference between methanol dehydrogenation and WGS reaction play an important role in determining the activity and CO₂ selectivity. Our study paves the way for the further rational design of single site catalysts at the atomic scale. Furthermore, the development of such highly efficient and selective hydrogen evolution systems promises to deliver highly desirable economic and ecological benefits.

The facet effect of ceria nanoparticles on platinum dispersion and catalytic activity of methanol partial oxidation

The effect of platinum-supported nano-shaped ceria catalysts on methanol partial oxidation and methyl formate product selectivity has been investigated. A Pt-supported CeO2 nanocube catalyst had a higher turnover frequency than nanosphere catalysts; however, nanosphere catalysts showed higher selectivity towards methyl formate. The observed ceria shape effect in catalysis was associated with the shape-dependent Pt dispersion and its oxidation states. Furthermore, in situ studies revealed that the reduced platinum and mono-dentate methoxy group were responsible for the higher turnover frequency.