Lattice Oxygen Species Research Articles

Understanding the Different Roles of Adsorbed Oxygen and Lattice Oxygen Species in the Distinct Catalytic Performance of Metal Oxides for o-Xylene Oxidation

Understanding the Different Roles of Adsorbed Oxygen and Lattice Oxygen Species in the Distinct Catalytic Performance of Metal Oxides for <i>o</i>-Xylene Oxidation

Highly Reversible Zn Anode Design Through Oriented ZnO(002) Facets.

The practical implementation of aqueous Zn-ion batteries presents formidable hurdles, including uncontrolled dendrite growth, water-induced side reactions, suboptimal Zn metal utilization, and intricate Zn anode manufacturing. Here, large-scale construction of a highly oriented ZnO(002) lattice plane on Zn anode (ZnO(002)@Zn) with thermodynamic inertia and kinetic zincophilicity is designed to address such problems. Both theoretical calculations and experiment results elucidate that the ZnO(002)@Zn possesses high Zn chemical affinity, hydrogen evolution reaction suppression, and dendrite-free deposition ability due to the abundant lattice oxygen species in ZnO(002) and its low lattice mismatch with Zn(002). These features synergistically promote ion transport and enable homogeneous Zn deposition. Consequently, the ZnO(002)@Zn anode displays a stable and prolonged cycling lifespan exceeding 500h even under a larger depth of discharge (85.6%) and realizes an impressive average Coulombic efficiency of 99.7%. Moreover, its efficacy is also evident in V2O5-cathode coin cells and pouch cells with not only high discharge capacity but also exceptional cycling stability. This integrated approach presents a promising avenue for addressing the challenges associated with Zn metal anodes, thereby advancing the prospects of aqueous Zn-ion battery technologies.

A study on the evolution of hydrothermally synthesized MoS2 on thermal annealing and development of novel MoS2-MoO3 hybrid nanostructure for supercapacitor applications

The electrochemical capacitor also known as supercapacitor is a high-performance energy storage device with exceptional properties. We report the evolution of structural, morphological, optical, and thermal properties of MoS2 on thermal annealing along with its supercapacitor study. The pristine MoS2 is synthesized via the hydrothermal method at 200°C and the material is annealed in the presence of air at 250°C, 300°C, and 350°C. The 300°C annealed sample has shown a hybrid MoO3-xMoS2-y phase characterized by morphology of mixed flower-like and nano brick-like structures, marking the first time report of this novel formation. The evolution of the novel MoO3-xMoS2-y phase can be attributed to the intervention of lattice and interstitial oxygen species during synthesis. Electrochemical analysis is employed to study the supercapacitor nature of the materials. The electrochemical study revealed that the hybrid structure has a higher charge storage capacity than MoS2 or MoO3. The calculated specific capacitance from the galvanostatic charge-discharge curve of MoO3-xMoS2-y in 0.1M NaOH is observed to be 1.71mF/cm2, five times greater than other samples. Furthermore, the capacitor behavior of MoO3-xMoS2-y is studied in different electrolytes such as KOH, NaOH, and Na2SO4 at a concentration of 3M. The intercalation-assisted faradaic process is observed to be the major charge storage mechanism of the hybrid structure. Developing novel nanostructures with distinct properties is crucial for advancing supercapacitors to achieve optimal performance.

Insights into the role of A/B-site substitution in chemical looping gasification of cotton stalk for enhanced syngas production over La-Co-O based perovskite oxygen carriers

Biomass chemical looping gasification (BCLG) is an emerging technology for efficient and clean utilization of cotton stalk (CS) to produce high-quality syngas. Among various oxygen carriers, perovskite oxides are holding an ever-increasing position in BCLG due to their unique structural properties and compositional flexibilities. However, research on perovskite-type oxygen carriers mostly focused on Fe-based oxides, and there is little in-depth investigation of Co-based perovskite and the role of A/B site substitution in the BCLG process. Herein, the LaCoO3 perovskite is selected as the basic oxygen carrier, and Sr, Fe are further doped on the A/B-site to form LaCo1-xFexO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) and La1-ySryCoO3 (y = 0, 0.2, 0.4, 0.6, 0.8) series. Effects of perovskite type, gasification temperature, steam volume fraction and oxygen carrier mass fraction of the BCLG performance are investigated. Results indicate that La0.6Sr0.4CoO3 and LaCo0.2Fe0.8O3 exhibit enhanced syngas production with the maximum of 1.304 m3/kg and 1.188 m3/kg, respectively, and outstanding cyclic stability at optimal reaction conditions. Further characterizations including H2-TPR, XPS and EPR analysis reveal that Sr substitution facilitate the formation of oxygen vacancies and adsorbed oxygen species, while Fe doping leads to the increasing concentration of oxygen vacancies and surface lattice oxygen species. Combined with the experimental and characterization results, it is deduced that the oxygen vacancies which promote the adsorption of reactants and accelerate the migration of bulk lattice oxygen, play the key role in the enhanced BCLG performance.

Defect engineering on Ce2Co1Cu1Ox catalyst surface via NaOH modification: Boosting the catalytic oxidation toluene performance by reducing intermediates and increasing ring-open ability of benzoate

Catalytic oxidation is still an effective approach to eliminate volatile organic compound (VOCs). In order to explore the promotion mechanism for the improvement of toluene oxidation capacity over NaOH-modified Ce2Co1Cu1 catalyst (Ce2Co1Cu1-AT), NaOH-modified catalysts with similar physical-structure and chemical properties were prepared by modified co-precipitation, impregnation and etching methods, respectively. Characterization results revealed that NaOH modification could generate a large number of defects, oxygen vacancies as well as abundant active sites on the surface of Ce2Co1Cu1, the concentration of surface adsorbed oxygen species and the mobility of surface lattice oxygen species were both increased. Hence, the catalyst's redox capacity was enhanced, the accumulation rates of benzyl alcohol and benzaldehyde were much lower (reduced about 69 % and 83 %, respectively), and the negative effect of the accumulation of intermediate species covering the reactive site was weakened. Benefiting from these, the toluene oxidation performance of the NaOH-modified catalysts was significantly improved, with T90 (191 ℃) of Ce2Co1Cu1-AT was nearly 20 ℃ lower than that of the un-modified catalyst, which is among the best reported activity values. Additionally, it also exhibited excellent thermal stability and water resistance. This work may provide a new strategy to design and synthesize the high-efficiency VOCs catalyst.

Lattice-confined Ag over MnCoLDH accelerated catalytic oxidation of formaldehyde at ambient temperature: The novel pathway with different oxygen species

Catalytic oxidation of formaldehyde (HCHO) at ambient temperature represents a cost-effective and efficient strategy for indoor HCHO removal. Although precious metal-based catalysts have been considered practical for oxidizing gaseous HCHO indoors, the limited activity of Ag-based catalysts can be attributed to their typical +1 and 0 valence states, as well as their single electron transport pathway. This characteristic impedes the reestablishment of the low state during oxygen activation, thereby resulting in catalyst deactivation. The present study successfully incorporated Ag atoms into manganese-cobalt layered double hydroxide (MnCoLDH) through doping, resulting in the development of a catalyst that exhibited complete formaldehyde oxidation activity at 30 °C. Lattice-confined Ag enables continuous activation of oxygen, while LDH facilitates the sustained provision of surface hydroxyl groups. The roles and mechanisms of surface hydroxyl groups, adsorbed oxygen, and lattice oxygen in the oxidation of formaldehyde were investigated using in-situ DRIFTS. By comparing Ag with the impregnation method, the confinement of Ag within the lattice enables continuous activation of oxygen. This study presents a viable strategy for designing efficient catalysts for volatile organic compounds (VOCs) removal by utilizing active lattice oxygen species.

Understanding of mercury/oxygen reaction mechanism over BiOBr photocatalyst with oxygen vacancy

BiOBr with the advantage of easily generated surface oxygen vacancy, has been considered as a promising photocatalyst for Hg0 oxidation in the flue gas and the active oxygen species is crucial for the oxidation reaction. Nevertheless, the detailed mercury/oxygen reaction mechanism on the BiOBr surface is still unclear and the effect of oxygen vacancy on the reaction process was worth in-depth study. Herein, the oxygen-involved Hg0 oxidation mechanism on the BiOBr surface and the effect of oxygen vacancy were deeply understood by quantum chemistry calculation. The reactivity difference of chemisorbed and lattice oxygen species was revealed. Therein, the chemisorbed oxygen derived from the activation of gaseous O2 molecule showed the higher reactivity than lattice oxygen for Hg0 oxidation reaction. The introduction of oxygen vacancy could promote O2 activation and simultaneously reduce the energy barrier of HgO formation from 1.76 to 1.45 eV. In addition, the energy barrier of oxygen vacancy recovery (0.05 eV) was higher than that of O2 activation (0.02 eV), indicating that the initial oxygen vacancy could be retained in the reaction process. This work deeply revealed the mercury/oxygen reaction mechanism over BiOBr photocatalyst and provided the guidance for the catalyst design in the photocatalytic Hg0 oxidation.

Magnesium borate whiskers/La2-XCeXZr2O7 catalysts preparation on cordierite honeycomb ceramic surfaces for soot catalytic oxidation͏

Magnesium borate whiskers were used to prepare a hierarchical microstructure on cordierite ceramic substrate through the precipitation-molten salt method. The La2-XCeXZr2O7 catalyst was then loaded onto the magnesium borate whiskers to form the hierarchical microstructure. The Ce-doped catalysts exhibited a significant improvement in the catalytic activity of soot combustion compared to the La2Zr2O7 catalyst. The study employed various techniques to characterize the structural morphology and phase composition, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform-infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The growth of Magnesium borate whiskers (Mg2B2O5) with diameters of 100–200 nm and lengths of 2–5 μm were grown and tightly bonded to the cordierite ceramic substrate to mimic the structure of human respiratory system cilia. This could improve the filtration efficiency of soot in car exhaust. BET analysis showed that the specific surface area of cordierite increased from 0.684 m2/g to 1.363 m2/g after whisker growth. The study confirmed that the whiskers were firmly attached to the cordierite ceramic substrate, as demonstrated by the binding strength experiments. The addition of Ce metal has been found to significantly enhance soot combustion due to the presence of more active oxygen species and superior mobility of lattice oxygen species with more oxygen vacancies. The catalyst's intrinsic redox property was characterized using X-ray photoelectron spectroscopy (XPS) and H2 temperature-programmed reduction (H2-TPR). The semi-quantitative thermogravimetric analysis (TG-DTG) and the temperature-programmed oxidation (TPO) of catalysts showed that Z-La1.9Ce0·1Zr2O7 exhibited the highest catalytic activity for soot combustion, with an ignition temperature of 268 °C, a peak temperature of 418 °C, and a temperature of 90 % soot conversion of 464 °C. Furthermore, cyclic stability experiments demonstrate that the Z-La1.9Ce0·1Zr2O7 catalyst exhibits excellent structural stability and consistent catalytic performance. This distinctive microstructure holds great potential for applications in the field of DPF.

K2SO4-promoted TiO2 for the efficient oxidative coupling of methane

The oxidative coupling of methane (OCM) into C2−3 hydrocarbons is still limited to a few types of catalysts with low product yield. Herein, we reported our discovery that a K2SO4-promoted TiO2 catalyst can effectively catalyze the OCM reactions with a C2−3 yield of up to 26 %, which is comparable to the classical Mn-NaWOx/SiO2 catalyst. Besides, this catalyst not only exhibits promising stability for at least 200 h without signs of deactivation under typical OCM conditions but also demonstrates high sulfur-resistance performance, outperforming most reported catalysts. We have evidenced that K+ ions are responsible for increasing the surface basicity of rutile TiO2, thus benefiting C2−3 selectivity. The presence of SO42− can prevent the formation of potassium titanates, which catalyze the over-oxidation of CH4. The surface lattice oxygen species are confirmed to be the active sites for selective CH4 activation, while the chemisorbed oxygen species catalyze the combustion of CH4 to CO2.

Dimethyl Carbonate Synthesis from CO2 over CeO2 with Electron‐Enriched Lattice Oxygen Species

AbstractDirect synthesis of dimethyl carbonate (DMC) from CO2 plays an important role in carbon neutrality, but its efficiency is still far from the practical application, due to the limited understanding of the reaction mechanism and rational design of efficient catalyst. Herein, abundant electron‐enriched lattice oxygen species were introduced into CeO2 catalyst by constructing the point defects and crystal‐terminated phases in the crystal reconstruction process. Benefitting from the acid‐base properties modulated by the electron‐enriched lattice oxygen, the optimized CeO2 catalyst exhibited a much higher DMC yield of 22.2 mmol g‐1 than the reported metal‐oxide‐based catalysts at the similar conditions. Mechanistic investigations illustrated that the electron‐enriched lattice oxygen can provide abundant sites for CO2 adsorption and activation, and was advantageous of the formation of the weakly adsorbed active methoxy species. These were facilitating to the coupling of methoxy and CO2 for the key *CH3OCOO intermediate formation. More importantly, the weakened adsorption of *CH3OCOO on the electron‐enriched lattice oxygen can switch the rate‐determining‐step (RDS) of DMC synthesis from *CH3OCOO formation to *CH3OCOO dissociation, and lower the corresponding activation barriers, thus giving rise to a high performance. This work provides insights into the underlying reaction mechanism for DMC synthesis from CO2 and methanol and the design of highly efficient catalysts.

Dimethyl Carbonate Synthesis from CO2 over CeO2 with Electron-Enriched Lattice Oxygen Species.

Direct synthesis of dimethyl carbonate (DMC) from CO2 plays an important role in carbon neutrality, but its efficiency is still far from the practical application, due to the limited understanding of the reaction mechanism and rational design of efficient catalyst. Herein, abundant electron-enriched lattice oxygen species were introduced into CeO2 catalyst by constructing the point defects and crystal-terminated phases in the crystal reconstruction process. Benefitting from the acid-base properties modulated by the electron-enriched lattice oxygen, the optimized CeO2 catalyst exhibited a much higher DMC yield of 22.2 mmol g-1 than the reported metal-oxide-based catalysts at the similar conditions. Mechanistic investigations illustrated that the electron-enriched lattice oxygen can provide abundant sites for CO2 adsorption and activation, and was advantageous of the formation of the weakly adsorbed active methoxy species. These were facilitating to the coupling of methoxy and CO2 for the key *CH3OCOO intermediate formation. More importantly, the weakened adsorption of *CH3OCOO on the electron-enriched lattice oxygen can switch the rate-determining-step (RDS) of DMC synthesis from *CH3OCOO formation to *CH3OCOO dissociation, and lower the corresponding activation barriers, thus giving rise to a high performance. This work provides insights into the underlying reaction mechanism for DMC synthesis from CO2 and methanol and the design of highly efficient catalysts.

Specific roles of lattice oxygen and asymmetric interface Cu-[Ox]-Ce structure-relating chemisorbed oxygen over CuO/CeO2 on the catalysis of benzene combustion

Copper-ceria catalysts exhibit high prospects in the catalysis of VOCs combustion, during which lattice oxygen and chemisorbed oxygen species play indispensable roles. However, understanding their specific operating mechanisms still remains a challenge. Shaped CeO2 and CuO/CeO2 counterparts were synthesized for benzene catalytic combustion. Pure CeO2, especially for nanorod-CeO2, possessed high low-temperature activity (LTA) due to numerous active lattice oxygen following the initial step of Mars-van Krevelen mechanism. Conversely, the impaired LTA (15–40 °C upshift at 15 % conversion) but improved high-temperature activity (HTA) were obtained by varying surface local environment upon CuO loading. 5 wt% CuO/nanoparticle-CeO2 exhibited the highest mobile chemisorbed oxygen relating to the strong oxygen transfer capacity of asymmetric interface Cu-[Ox]-Ce structures affected by ceria crystal planes and sizes was verified by density functional theory calculations and experiments, despite the strong CuO-CeO2 synergistic effects. This study provides a promising direction for engineering benzene degradation catalysts with excellent low-temperature performance.

Chlorobenzene Oxidation over Phosphotungstic-Acid-Coated Cerium Oxide: Synergistic Effect of Phosphotungstic and Cerium Oxide and Inhibition Mechanism of Sulfur Dioxide

Ce–based catalysts exhibit a poor stability and activity in chlorinated volatile organic compound (Cl–VOC) oxidation due to their rapid Cl poisoning. Herein, phosphotungstic acid (HPW) was coated on CeO2 to improve its activity and stability for chlorobenzene (CB) oxidation. The HPW coating not only promoted CB adsorption onto CeO2, but also provided Brønsted acid sites to CeO2 for Cl species removal as HCl, thus avoiding Cl poisoning. Hence, a synergistic effect of CeO2 and HPW on HPW/CeO2 was observed, resulting in superior CB oxidation activity and stability. Additionally, to improve the sulfur resistance of the catalyst, the inhibition mechanism of SO2 on CB oxidation by HPW/CeO2 was explored. HPW/CeO2 was prone to sulfation due to the formation of Ce2(SO4)3 from the reaction of SO2 and CeO2. Thus, the oxidation ability of HPW/CeO2; the amount of adsorption sites for CB adsorption; and the amounts of Ce4+ bonded with O2−, lattice oxygen species, and adsorbed oxygen species were decreased by SO2. Meanwhile, SO2 competed with CB for the adsorption sites on HPW/CeO2. Therefore, CB oxidation by HPW/CeO2 was remarkably restrained by SO2. The present work promotes further work on Cl–VOC removal by Ce-based catalysts for anti-SO2 poisoning modification in the future.

Hierarchical MOFs with Good Catalytic Properties and Structural Stability in Oxygen-Rich and High-Temperature Environments.

Metal-organic framework materials are ideal materials characterized by open frameworks, adjustable components, and high catalytic activity. They are extensively utilized for catalysis. Due to decomposition and structural collapse under high temperatures and an oxygen-rich environment, the potential of thermal catalysis is greatly limited. In this research, Co-rich hollow spheres (Co-HSs) with a gradient composition are designed and synthesized to investigate their thermal catalytic properties in the ammonium perchlorate（AP）system. The results demonstrate that Co-HSs@AP exhibits good thermal catalytic activity and a high-temperature decomposition of 292.5 °C, which is 121.6 °C lower than pure AP. The hierarchical structure confers structural stability during the thermal decomposition process. Thermogravimetry-infrared indicates that the inclusion of Co-HSs successfully boosts the level of reactive oxygen species and achieves thorough oxidation of NH3. Based on the above phenomenon, macro dynamics calculations are carried out. The results show that Co-HSs can promote the circulation of lattice oxygen and reactive oxygen species and the multidimensional diffusion of NH3 in an oxygen-rich environment. This material has significant potential for application in the fields of thermal catalysis and ammonia oxidation.

Oxygen Dynamics in Lean Propylene Catalytic Combustion over CeO2 and Pr6O11: Roles and Interplay between Lattice and Adsorbed Oxygen Species

Oxygen Dynamics in Lean Propylene Catalytic Combustion over CeO₂ and Pr₆O₁₁: Roles and Interplay between Lattice and Adsorbed Oxygen Species

Catalytic Oxidation of Chlorobenzene over HSiW/CeO2 as a Co-Benefit of NOx Reduction: Remarkable Inhibition of Chlorobenzene Oxidation by NH3.

There is an urgent need to develop novel and high-performance catalysts for chlorinated volatile organic compound oxidation as a co-benefit of NOx. In this work, HSiW/CeO2 was used for chlorobenzene (CB) oxidation as a co-benefit of NOx reduction and the inhibition mechanism of NH3 was explored. CB oxidation over HSiW/CeO2 primarily followed the Mars-van-Krevelen mechanism and the Eley-Rideal mechanism, and the CB oxidation rate was influenced by the concentrations of surface adsorbed CB, Ce4+ ions, lattice oxygen species, gaseous CB, and surface adsorbed oxygen species. NH3 not only strongly inhibited CB adsorption onto HSiW/CeO2, but also noticeably decreased the amount of lattice oxygen species; hence, NH3 had a detrimental effect on the Mars-van-Krevelen mechanism. Meanwhile, NH3 caused a decrease in the amount of oxygen species adsorbed on HSiW/CeO2, which hindered the Eley-Rideal mechanism of CB oxidation. Hence, NH3 significantly hindered CB oxidation over HSiW/CeO2. This suggests that the removal of NOx and CB over this catalyst operated more like a two-stage process rather than a synergistic one. Therefore, to achieve simultaneous NOx and CB removal, it would be more meaningful to focus on improving the performances of HSiW/CeO2 for NOx reduction and CB oxidation separately.

Engineering lattice oxygen mobility and optimizing reaction pathway via tuning Cu-Co interactions for efficient elimination of volatile organic compounds: A metal–organic framework template approach

Incorporating a secondary metal into individual cobalt oxides has been viewed as an efficacious approach in creating intermetallic interactions. Nonetheless, the processes involved in the construction of intermetallic interactions, as well as the underlying mechanisms that contribute to catalytic activity, remain largely elusive in current scientific understanding. In this work, a range of Cu-Co bimetallic oxides were synthesized through various preparation methods, employing MOFs as templates. Notably, the hydrothermally-synthesized Cu/Co-HT catalyst exhibited impressive catalytic qualities for toluene combustion, with T50 = 229 °C and T90 = 239 °C, alongside exceptional stability and moisture resistance (under 10 vol. % of water) for at least 100 h. The optimal catalyst Cu/Co-HT is attributed to the stronger Cu-Co interaction, which leading to larger specific surface area and weaker Co-O bond strength. And it also affects the chemical properties, such as get more Co3+ and lattice oxygen species by a redox (Co2++Cu2+→Co3++Cu+), better electron transfer performance and low-temperature reducibility. In addition, the reaction mechanism of toluene over the surface of Cu/Co-HT was also revealed by in-situ DRIFTS. It was observed that the bimetallic catalyst, characterized by robust Cu-Co interactions, optimized the reaction pathway for toluene oxidation compared to pure Co3O4. This facilitation led to the direct conversion of benzyl alcohol into benzoate and carboxylate, thereby bypassing the intermediate step involving benzaldehyde, which enhancing the reaction speed, yielding a long-term stable and efficient operational performance. This study reveals that optimize the physicochemical properties of catalytic by enhancing bimetallic interactions is an effective strategy for improving catalytic behavior.

MOF-derived FeOx with highly dispersed active sites as an efficient catalyst for enchaning catalytic oxidation of VOCs

Highly efficient and stable catalysts serve as the crucial factor in VOCs catalytic oxidation technology. Iron-based materials are recognized as potential VOCs catalysts due to their cost-effectiveness and non-toxic nature. However, the limited catalytic performance of traditional iron oxide catalysts hinders their further industrial applications. A series of FeOx catalysts were synthesized via pyrolysis of Fe-based MOFs with diverse morphologies for toluene catalytic oxidation. Characterization results demonstrated that the FeOx-100 catalyst performed optimal characteristics, including the abundant specific surface area and smaller crystallite size, which offered highly dispersed active sites and defects for toluene oxidation. The catalytic activity of FeOx-100 was improved by adjusting the precursors and pyrolysis conditions, achieving a 50% toluene conversion at 223 °C and 90% conversion at 249 °C. The redox abilities of FeOx catalysts were carefully evaluated to assess their impact on catalytic activity. The results confirmed that FeOx-100 exhibited superior low-temperature reducibility, remarkable presence of surface active oxygen and lattice oxygen species, jointly facilitating the toluene oxidation performance at lower temperatures. The results of in situ DRIFTS provided evidence supporting a degradation pathway for toluene, likely proceeding as follows: toluene→ benzaldehyde→ benzoate→ anhydride → …→ CO2 and H2O.

Enhanced ability of toluene oxidation by controlling inversion degree of spinel composed of only Co, Mn

Exploring the single relationship between the inversion degree of spinel and its catalytic performance is a great challenge, but has important significance for further structural design and application. A series of CoMn inverse spinels were prepared and the general formula Co1-x2+Cox3+tetMn13+Cox2+Co1-x3+octO4 was deduced through X-ray diffraction refinement to find a decreased inversion degree x as calcination temperature rose. Catalytic oxidation of toluene showed that higher inversion degree (S-300 with x ≈ 0.95) can reach larger conversion rate (90 % at about 250 °C for 400 ppm toluene) with greater reaction stability (140 h). Density Functional Theory (DFT) calculations on density of states indicated its metallic nature, and found that the strength of O-p and Transition metal-d orbitals at Fermi energy is positively correlated to the inversion degree, meaning stronger electron migration ability. Along with the adsorption calculation analysis that lattice oxygen species are proved to work dominantly (S-300 with lowest adsorption energy but highest performance), this work uncovered a theoretical insight into inverse spinel oxide, to provide the possibility of elevated oxidation ability through structural control.

Catalytic oxidation of propane over nanorod-like TiO2 supported Ru catalysts: Structure-activity dependence and mechanistic insights

Nanorod-like titanium dioxide (TiO2-Rod) supported ruthenium catalysts with variable metal loadings (designated as x-Ru/TiO2-Rod, x = 0.1, 0.5, 1.0 and 1.5 wt.%) were prepared for the catalytic oxidation of propane. The unique nanorod-like structure and high specific surface area of TiO2-Rod support was favorable for the surface distribution of ruthenium nanoparticles, constructing highly active redox sites for propane oxidation. Light-off experimental results indicated that the x-Ru/TiO2-Rod catalysts exhibited diverse catalytic activities for propane oxidation, giving a volcanic sequence of 0.1-Ru/TiO2-Rod < 0.5-Ru/TiO2-Rod < 1.5-Ru/TiO2-Rod < 1.0-Ru/TiO2-Rod with the increasing ruthenium content. Additionally, the optimal 1.0-Ru/TiO2-Rod delivered adequate catalytic stability and CO2/water resistant ability under complex industrial conditions. Characterization results revealed that the metallic Ru0 and the surface lattice oxygen species from the Ru-TiO2 interface were demonstrated to be the catalytic active components, which played an essential role in the reaction. In situ DRIFTs analysis verified the formation of acetate, acetone and formate species as the predominant organic intermediates in propane oxidation, which may result from two plausible reaction pathways depending on the activation of terminal methyl group (–CH3) and the central methylene (CH2) group in propane molecule. This work provides fundamental guidance for the development of Ru-based catalysts and the reaction mechanism understanding for light alkanes oxidation.