Total Oxidation of Propane over a Ru/CeO2 Catalyst at Low Temperature

Thermal Stability of Ru–Re NPs in H2 and O2 Atmosphere and Their Activity in VOCs Oxidation: Effect of Ru Precursor

The thermal stability of Ru–Re NPs on γ-alumina support was studied in hydrogen at 800 °C and in air at 250–400 °C. The catalysts were synthesized using Cl-free and Cl-containing Ru precursors and NH4ReO4. Very high sintering resistance of Ru–Re NPs was found in hydrogen atmosphere and independent of Ru precursors and Re loading, the size of them was below 2–3 nm. In air, metal segregation occurred at 250 °C, leading to formation of RuO2 and highly dispersed ReOx species. Ruthenium agglomeration was hindered at higher Re loading and in presence of residual Cl species. Propane oxidation rate was higher with the Ru(N)–Re catalysts than with Ru(N) and that containing Cl species. The Ru(N)–Re (3:1) catalyst exhibited the highest activity and the lowest activation energy (91.6 kJ mol−1) what is in contrast to Ru(Cl)–Re (3:1) which had the lowest activity and the highest activation energy (119.3 kJ mol−1). Thus, the synergy effect was not observed in Cl-containing catalysts.

Graphic Abstract

HCl-Tolerant HxPO4/RuOx-CeO2 Catalysts for Extremely Efficient Catalytic Elimination of Chlorinated VOCs

Bulk metal doping and surface phosphate modification were synergically adopted in a rational design to upgrade the CeO₂ catalyst, which is highly active but easily deactivated for the catalytic oxidation of chlorinated volatile organic compounds (Cl-VOCs). The metal doping increased the redox ability and defect sites of CeO₂, which mostly promoted catalytic activity and inhibited the formation of dechlorinated byproducts but generated polychlorinated byproducts. The subsequent surface modification of the metal-doped CeO₂ catalysts with nonmetallic phosphate completely suppressed the formation of polychlorinated byproducts and, more importantly, enhanced the stability of the surface structure by forming a chainmail layer. A highly active, durable, and selective catalyst of phosphate-functionalized RuO_x-CeO₂ was the most promising among all the metal-doped (Ru, Pd, Pt, Cr, Mn, Fe, Co, and Cu) CeO₂ catalysts investigated owing to the prominent chemical stability of RuO_x and its superior versatility in the catalytic oxidation of different kinds of Cl-VOCs and other typical pollutants, including dimethyl sulfide, CO, and C₃H₈. Moreover, the chemical stability of the catalyst, including its bulk and surface structural stability, was investigated by combining intensive treatment with HCl/H₂O or HCl with subsequent ex situ ultraviolet-visible light Raman spectroscopy and confirmed the superior resistance to Cl poisoning of the phosphate-functionalized RuO_x-CeO₂. This work exemplifies a promising strategy for developing ideal catalysts for the removal of Cl-VOCs and provides a catalyst with the superior catalytic performance in Cl-VOC oxidation to date.

Highly efficient Ru/CeO2 catalysts for formaldehyde oxidation at low temperature and the mechanistic study

Ru species have a high redox capacity on a CeO₂ support, and the metallic Ru species could be easily oxidized back to RuO_x species.

The effects of MoO3 impregnation order on the catalytic activity for propane combustion over Pt/ZrO2 catalysts: the crucial roles of Pt–MoO3 interfacial sites density

MoO₃ promoted Pt/ZrO₂ catalysts were prepared by co-impregnation (Pt–Mo/ZrO₂) or stepwise impregnation (Pt/Mo/ZrO₂ and Mo/Pt/ZrO₂) for propane combustion.

Comparison study of the effect of CeO2-based carrier materials on the total oxidation of CO, methane, and propane over RuO2

While activity and kinetics of catalytic CO and propane combustion over RuO2 depends sensitively on the carrier material, methane combustion on RuO2 is hardly affected by the carrier.

Comparison of Different Metal Doping Effects on Co3O4 Catalysts for the Total Oxidation of Toluene and Propane

Metal-doped (Mn, Cu, Ni, and Fe) cobalt oxides were prepared by a coprecipitation method and were used as catalysts for the total oxidation of toluene and propane. The metal-doped catalysts displayed the same cubic spinel Co3O4 structure as the pure cobalt oxide did; the variation of cell parameter demonstrated the incorporation of dopants into the cobalt oxide lattice. FTIR spectra revealed the segregation of manganese oxide and iron oxide. The addition of dopant greatly influenced the crystallite size, strain, specific surface area, reducibility, and subsequently the catalytic performance of cobalt oxides. The catalytic activity of new materials was closely related to the nature of the dopant and the type of hydrocarbons. The doping of Mn, Ni, and Cu favored the combustion of toluene, with the Mn-doped one being the most active (14.6 × 10−8 mol gCo−1 s−1 at 210 °C; T50 = 224 °C), while the presence of Fe in Co3O4 inhibited its toluene activity. Regarding the combustion of propane, the introduction of Cu, Ni, and Fe had a negative effect on propane oxidation, while the presence of Mn in Co3O4 maintained its propane activity (6.1 × 10−8 mol gCo−1 s−1 at 160 °C; T50 = 201 °C). The excellent performance of Mn-doped Co3O4 could be attributed to the small grain size, high degree of strain, high surface area, and strong interaction between Mn and Co. Moreover, the presence of 4.4 vol.% H2O badly suppressed the activity of metal-doped catalysts for propane oxidation, among them, Fe-doped Co3O4 showed the best durability for wet propane combustion.

The Influence of Residual Sodium on the Catalytic Oxidation of Propane and Toluene over Co3O4 Catalysts

A series of Co3O4 catalysts with different contents of residual sodium were prepared using a precipitation method with sodium carbonate as a precipitant and tested for the catalytic oxidation of 1000 ppm propane and toluene at a weight hourly space velocity of 40,000 mL g−1 h−1, respectively. Several techniques were used to characterize the physicochemical properties of the catalysts. Results showed that residual sodium could be partially inserted into the Co3O4 spinel lattice, inducing distortions and helping to increase the specific surface area of the Co3O4 catalysts. Meanwhile, it could negatively affect the reducibility and the oxygen mobility of the catalysts. Moreover, residual sodium had a significant influence on the catalytic activity of propane and toluene oxidation over the synthesized Co3O4 catalysts. The catalyst derived from the precursor washed three times presented the best activity for the catalytic oxidation of propane. The origin was traced to its better reducibility and higher oxygen mobility, which were responsible for the formation of active oxygen species. On the other hand, the catalyst obtained from the precursor washed two times exhibited better performance in toluene oxidation, benefitting from its more defective structure and larger specific surface area. Furthermore, the most active catalysts maintained constant performance in cycling and long-term stability tests of propane and toluene oxidation, being potentially applicable for practical applications.

Enhanced catalytic performance for volatile organic compound oxidation over in-situ growth of MnOx on Co3O4 nanowire

Hierarchical Co₃O₄@MnOx material has been synthesized by in-suit growth of MnOx on the Co₃O₄ and applied in catalytic oxidation of volatile organic compounds (VOCs). Results revealed that T₉₀ of acetone on the Co₃O₄@MnOx was 195 °C, which was 36 °C and 32 °C lower than that on the Co₃O₄ and MnOx/Co₃O₄, respectively. The universality experiments demonstrated that T₉₀ of ethyl acetate and toluene on the Co₃O₄@MnOx were 200 °C and 222 °C, respectively. The above results indicated that Co₃O₄@MnOx catalyst presented a robust catalytic performance. Characterization results showed that high catalytic activity of the Co₃O₄@MnOx catalyst could be attributed to the improvement of low temperature reducibility, the enhancement of Co³⁺ and adsorbed oxygen species resulted from the sufficient reaction between MnO₄^- and Co²⁺ during secondary hydrothermal process. Furthermore, stability and water-resistance experiments showed the Co₃O₄@MnOx catalyst with high cycle and long-term stability, satisfied endurability to 5.5-10 vol. % water vapor at 210 °C.

Three-dimensionally macroporous MnZrOx catalysts for propane combustion: Synergistic structure and doping effects on physicochemical and catalytic properties

Three-dimensionally macroporous (3DM) MnZrO_x catalysts were fabricated to reveal the structure and Zr-doping effects on both physicochemical properties and propane combustion behaviors. The increasing addition of zirconium is favorable for the formation of 3DM structure and amorphous Mn-Zr solid solution, leading to tunable physicochemical properties. The significant activity improvement after zirconium addition was originally attributable to the superior redox ability, higher oxygen mobility and more abundant oxygen vacancy. The excellent catalytic activity, cycling stability and water resistant ability over 3DM Mn_0.6Zr_0.4O_x make it a promising material for hydrocarbons elimination. The comparative TPSR, in situ DRIFTs and kinetics study over 3DM and bulk catalysts emphasize the advantageous function of 3DM architecture on promoting propane adsorption, oxidation and lattice oxygen mobility.

Ethylene glycol assisted synthesis of hierarchical Fe-ZSM-5 nanorods assembled microsphere for adsorption Fenton degradation of chlorobenzene

A unique zeolite catalyst, Fe doped ZSM-5 microsphere assembled by uniform nanorod-like crystals with hierarchical pore structure, was successfully synthesized and applied for the adsorption and degradation of trace chlorobenzene (CB) in the presence of H₂O₂. The organic ferric salts as the precursors, ethylene glycol as a chelating/reducing agent and the dynamic two-stage temperature-varied hydrothermal technique, together made the synthesized hierarchical Fe-ZSM-5 nanorods assembled microspheres (FZ-CA-5EG) to be characterized by abundant highly dispersed and valency-controlled framework Fe^3+/2+ species. As a result of these features, the FZ-CA-5EG showed excellent ability of adsorption and degradation efficiency of CB, and enhanced durability due to negligible leaching of framework Fe species. Moreover, the hydroxyl radicals were determined as the main the reactive oxygen species of CB oxidation degradation, and a possible adsorption-oxidation degradation pathway was proposed.

Hydroxyl groups attached to Co2+ on the surface of Co3O4: a promising structure for propane catalytic oxidation

Co₃O₄ catalysts with three specific morphologies (nanocubes, nanosheets, and nanooctahedra) were prepared using simple preparation methods and tested for catalytic combustion of propane under the same reaction conditions.

Ru/CeO2 Catalyst with Optimized CeO2 Support Morphology and Surface Facets for Propane Combustion

Tailoring the interfaces between active metal centers and supporting materials is an efficient strategy to obtain a superior catalyst for a certain reaction. Herein, an active interface between Ru and CeO₂ was identified and constructed by adjusting the morphology of CeO₂ support, such as rods (R), cubes (C), and octahedra (O), to optimize both the activity and the stability of Ru/CeO₂ catalyst for propane combustion. We found that the morphology of CeO₂ support does not significantly affect the chemical states of Ru species but controls the interaction between the Ru and CeO₂, leading to the tuning of oxygen vacancy in the CeO₂ surface around the Ru-CeO₂ interface. The Ru/CeO₂ catalyst possesses more oxygen vacancy when CeO₂-R with predominantly exposed CeO₂{110} surface facets is used, providing a higher ability to adsorb and activate oxygen and propane. As a result, the Ru/CeO₂-R catalyst exhibits higher catalytic activity and stability for propane combustion compared with the Ru/CeO₂-C and Ru/CeO₂-O catalysts. This work highlights a new strategy for the design of efficient metal/CeO₂ catalysts by engineering morphology and associated surface facet of CeO₂ support for the elimination of light alkane pollutants and other volatile organic compounds.

Continuous flow aerobic alcohol oxidation using a heterogeneous Ru0 catalyst

Stable Ru⁰ on γ-Al₂O₃ has been used for the selective aerobic oxidation of benzyl alcohol in flow.

Thermal stability and propane combustion activity of RhxCe1−xO2−y nanoparticles deposited on functionalized alumina

A new, effective method for stabilization of Rh_xCe_1−xO_2−y nanoparticles synthesized by the reverse microemulsion method by their deposition on functionalized alumina has been successfully applied for systems in a wide range of Rh contents (x ≤ 0.15).

Robust and well-controlled TiO2–Al2O3 binary nanoarray-integrated ceramic honeycomb for efficient propane combustion

Well-tuned TiO₂–Al₂O₃ binary nanoarrays had been fabricated onto ceramic honeycombs and exhibited excellent robustness and catalytic activity for propane oxidation.

Phosphate-Functionalized CeO2 Nanosheets for Efficient Catalytic Oxidation of Dichloromethane

Tuning the nature and profile of acidic and basic sites on the surface of redox-active metal oxide nanostructures is a promising approach to constructing efficient catalysts for the oxidative removal of chlorinated volatile organic compounds (CVOCs). Herein, using dichloromethane (DCM) oxidation as a model reaction, we report that phosphate (PO _x) Brønsted acid sites can be incorporated onto a CeO₂ nanosheet (NS) surface via an organophosphate-mediated route, which can effectively enhance the CeO₂'s catalytic performance by promoting the removal of chlorine poisoning species. From the systematic study of the correlation between PO _x composition, surface structure (acid and basic sites), and catalytic properties, we find that the incorporated Brønsted acid sites can also function to decrease the amount of medium-strong basic sites (O^2-), reducing the formation of chlorinated organic byproduct monochloromethane (MCM) and leading to the desirable product, HCl. At the optimized P/Ce ratio (0.2), the PO _x-CeO₂ NSs can perform a stable DCM conversion of 65-70% for over 10 h at 250 °C and over 95% conversion at 300 °C, superior to both pristine and other phosphate-modified CeO₂ NSs. Our work clearly identifies the critical role of acid and basic sites over functionalized CeO₂ for efficient catalytic CVOCs oxidation, guiding future advanced catalyst design for environmental remediation.

Sword-like CuO/CeO2 composites derived from a Ce-BTC metal–organic framework with superior CO oxidation performance

Porous shape-controllable metal oxide composites derived from a metal–organic framework have gained more and more attention due to their extensive applications.