Catalytic Combustion Activity Research Articles

Promoting Effect of Palladium on ZnAl2O4-Supported Catalysts Based on Cobalt or Copper Oxide on the Activity for the Total Propene Oxidation.

Palladium-modified Co-ZnAland Cu-ZnAl materials were used and found active for the catalytic oxidation of propene and propane. According to the results obtained by XRD, TPR and XPS, the zinc aluminate-supported phases are oxide phases, Co3O4, CuO and PdOx for Co-ZnAl, Cu-ZnAl and Pd-ZnAl catalysts, respectively. These reducible oxide species present good catalytic activity for the oxidation reactions. The addition of palladium to Co-ZnAl or Cu-ZnAl samples promoted the reducibility of the system and, consequently, produced a synergic effect which enhanced the activity for the propene oxidation. The PdCo-ZnAl sample was the most active and exhibited highly dispersed PdOx particles and surface structural defects. In addition, it exhibited good catalytic stability. The H2 pre-treated PdCu-ZnAl, PdCo-ZnAl and Pd-ZnAl samples showed higher activity than the original oxide catalysts, evidencing the important role of the oxidation state of the species, mainly of the palladium species, on the catalytic activity for the propene combustion. The synergic effect between metal transition oxides and PdOx could not be observed for the propane oxidation.

Methane combustion over palladium catalyst within the confined space of MFI zeolite

Isolated cationic Pd species encapsulated in MFI zeolite, i.e., Pd@MFI, have been successfully prepared via in situ hydrothermal route followed by oxidative treatment. The as-prepared Pd@MFI samples are investigated as promising catalysts in the reaction of methane combustion. Typically, Pd@H-ZSM-5 shows remarkable activity in methane catalytic combustion with a low apparent activation energy value of 70.7 kJ/mol as well as good catalytic stability even in excess water vapor. Detailed characterization results demonstrate the strong interaction between Pd sites and zeolite framework in Pd@ZSM-5 and the efficient stabilization of isolated Pd sites by zeolite thereof. Spectroscopy analyses reveal that the presence of Brønsted acid sites is beneficial to methane adsorption and its subsequent activation on adjacent Pd sites, constructing cooperation between Brønsted acid sites and Pd sites within the confined space of MFI zeolite toward high-efficiency methane catalytic combustion. The reaction mechanism of methane combustion catalyzed by Pd@H-ZSM-5 model catalyst is finally discussed.

Pt modulates the electronic structure of Pd to improve the performance of Pd-based catalytic combustion catalyst

The electronic modulation between the catalytic active components can improve the catalytic activity and stability of the catalyst. The Pd-based catalysts can easily react with SOX to form stable and inactive sulfates. In this paper, the Pd–Pt-based catalytic combustion catalyst was prepared by replacing part of Pd with a small amount of Pt. The storage tank VOCs catalytic combustion activity and the anti-SO2 poisoning performance of the Pd–Pt-based catalyst and Pd-based catalyst were tested. The Pd 3d binding energy of each Pd-based catalyst was detected by XPS characterization, and the electronic structure changes of Pd active components was analyzed by the change of Pd 3d binding energy. The effect of electrons transfer between Pd and Pt on the improvement of catalytic combustion activity and SO2 poisoning resistance of Pd-based catalysts was analyzed. The results show that the Pt addition can increase the electron cloud density of the Pd active components, and improve the performance of the Pd active components to adsorb and activate oxygen. The reaction of Pd and SOX to form sulfate needs to gain electrons. The increase in the electron cloud density of the Pd active components in Pd–Pt-based catalyst makes it difficult for the Pd active components to adsorb SOX and difficult to react with SOX to form sulfate, thereby preventing the Pd active components from being poisoned and deactivated.

Superior catalytic activity of Pd-based catalysts upon tuning the structure of the ceria-zirconia support for methane combustion

Pd-based catalysts supported on CeO2-ZrO2 (CZ) mixed oxides have been universally applied toward the oxidation of methane, a strong greenhouse gas. Herein, CZ supports of different structures were prepared using hydrothermal (ST-CZ), co-precipitation (CP-CZ), and physical mixing (Mix-CZ) methods. Subsequently, the effects of the CZ support structure on the catalytic activity of the resulting Pd/CZ catalysts toward methane combustion were evaluated. ST-CZ shows the presence of cubic and tetragonal phases of CZ solid solutions, while CP-CZ is a pure tetragonal-phase solid solution and Mix-CZ is a mixture of CeO2 and ZrO2. The CZ solid solution improved the Pd dispersion and Pd2+/Pd ratio on the catalyst surface. Furthermore, CZ oxides with a two-phase composite structure resulted in higher oxygen storage capacity and oxygen mobility in the Pd/CZ catalysts than in the pure solid solution phase. Therefore, the Pd/ST-CZ catalyst shows superior catalytic activity for methane combustion than the other two catalysts.

Hierarchically porous silica supported ceria and platinum nanoparticles for catalytic combustion of toluene

The hierarchically porous silica (NKM-5) was synthesized by the polyelectrolyte-surfactant mesomorphous complex templating method, and the NKM-5 was used as the carrier to load different amounts of ceria to prepare xCe/NKM-5 samples (x represents the CeO2 loading amount) by the impregnation method, and then supported Pt to prepare Pt/xCe/NKM-5 catalyst for toluene catalytic combustion. NKM-5 sample has excellent specific surface area and pore structure, with the increase of CeO2 loading amount, the specific surface area and pore volume of xCe/NKM-5 sample decreased gradually. As the CeO2 loading amount increased, XRD and TEM characterization showed that the Pt dispersion of Pt/xCe/NKM-5 catalyst increased; XPS results showed that the proportion of Pt0 decreased and the proportion of Ce3+ increased; H2-TPR characterization showed that the reducibility increased; and the interaction between Pt and CeO2 increased gradually. The toluene catalytic combustion activity of Pt/xCe/NKM-5 catalyst first increased and then decreased with the increase of CeO2 loading amount. Pt/30Ce/NKM-5 catalyst has the most excellent catalytic activity with 50% toluene conversion at 174 °C and 90% conversion at 195 °C, which is the result of the synergy effect of the hierarchical pore structure of the support and the metal-support interaction between Pt and CeO2.

Phosphate-assisted synthesis of ultrathin and thermally stable alumina nanosheets as robust Pd support for catalytic combustion of propane

Two-dimensional γ-Al2O3 nanosheet with rich pentacoordinate Al3+ sites which can nicely stabilize noble metals via strong interactions between metal and support has been focused. However, the synthesis of ultrathin and highly thermal-stable Al2O3 is challenging. Herein, we report an effective approach to synthesize ultrathin Al2O3 nanosheets with regular leaf-like architecture as well as high thermal-stability. A novel intercalation-swelling-exfoliation pathway was proposed to elucidate the formation of ultrathin sheet-like structure and then its morphology/thickness could be further adjusted via a dissolution-growth induced by phosphate. Meanwhile, the presence of phosphate further enhanced thermal stability of Al2O3 nanosheets due to the occupation or depletion of high-reactive sites and surface hydroxy groups. Subsequently, the thermally stable γ-Al2O3 nanosheets with moderate anchoring sites was used as a support of Pd and investigated for catalytic combustion of propane. The Pd/Al2O3 nanosheet exhibited a superior catalytic activity for propane combustion and the complete conversion was below 300 °C, more importantly, the outstanding resistance to high temperature (1000 °C) was observed, which was ascribed to the re-dispersion of Pd particles and the occurrence of strong metal-support interaction (SMSI) at high temperature.

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.

Investigation of perovskite BaCe1-xMnxO3-δ for methane combustion

The Mn-doped BaCeO3 series composite oxide catalysts were prepared by a sol-gel method. The low-temperature catalytic methane combustion activity test of BaCe1-xMnxO3-δ series composite oxide catalysts at low temperature (200-600 °C) was studied in a fixed bed reactor. The physical properties of the catalyst were characterized by XRD, SEM, particle size analysis and specific surface area measurement, and the conductivity of the sample was measured by AC impedance spectroscopy. Research shows that: the perovskite phase composite oxide catalyst was successfully prepared by the sol-gel method, and the prepared perovskite phase catalyst has good catalytic performance and high temperature stability. The catalytic performance of the catalyst changes with the conductivity, which shows a proportional relationship; when the temperature is lower than 650 °C, Mn doping significantly improves the catalytic activity of the BaCeO3 catalyst for methane combustion. The catalytic activity increases initially and then decreases with the doping amount of Mn. When the doping amount is 0.4 the catalyst has the best catalytic activity, with the ignition temperature of methane at as low as 249.7 °C, and the catalytic methane complete conversion temperature T90 (The corresponding temperature when CH4 conversion rate is 90%) at 423.2 °C. This work is of considerable referential importance in the optimization design of catalysts for CH4 combustion at low temperature.

Engineering the Nucleophilic Active Oxygen Species in CuTiOx for Efficient Low-Temperature Propene Combustion.

Industrialization has resulted in the rapid increase of volatile organic compound (VOC) emissions, which have caused serious issues to human health and the environment. In this study, an extensive Cu incorporating TiO2 induced nucleophilic oxygen structure was constructed in the CuTiOx catalyst, which exhibited superior low-temperature catalytic activity for C3H6 combustion. Thorough structural, surface characterization and density functional theory (DFT) calculations revealed that the Cu-O-Ti hybridization induced nucleophilic oxygen initiates C3H6 combustion by abstracting the C-H bond. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results indicated that incorporated copper species acted as the major adsorbent site for the propene molecule. In combination of the DRIFTS and DFT results, the promotion effect of the nucleophilic O on the C-H bond abstraction and CO2 formation pathway was proposed. The surface doping induced nucleophilic oxygen as strong Brønsted basic sites for low-temperature propene combustion exemplified an efficient strategy for rational design of next-generation environmental catalysts.

Optimized Pt-MnOx interface in Pt-MnOx/3DOM-Al2O3 catalysts for enhancing catalytic soot combustion

The catalysts of three-dimensionally ordered macroporous (3DOM) Al2O3-supported core-shell structured Pt@MnOx nanoparticles (3DOM-Pt@MnOx/Al2O3) were successfully prepared by the gas bubbling-assisted membrane reduction-precipitation (GBMR/P) method. Pt@MnOx core-shell nanoparticles (NPs) are highly dispersed on the inner surface of 3DOM-Al2O3 support. Pt@MnOx/3DOM-Al2O3 catalysts, which combine both advantages of high-efficiency soot-catalyst contact by 3DOM-Al2O3 structure and the abundant active sites by the optimized Pt-MnOx interface, exhibit high catalytic activities for soot combustion, and the catalytic activities are strongly dependent on the thickness of MnOx shell. Among the catalysts, 3DOM-Pt@MnOx/Al2O3-1 catalyst with optimized Pt-MnOx interface shows the highest catalytic activity for soot combustion, i.e., its values of T50 and SCO2m are 351 °C and 98.6%, respectively. The highest density of Pt-MnOx active sites for adsorption-activation of gaseous O2 is responsible for enhancing catalytic activity for soot combustion. Pt@MnOx/3DOM-Al2O3 catalysts are promising to practical applications for the emission reduction of soot particles.

Catalytic combustion of vinyl chloride emissions over Co3O4 catalysts with different crystallite sizes

A series of Co3O4 catalysts was prepared by ammonia (Co-AP) and oxalate (Co-OP) precipitation, sol–gel (Co-SG), and urea hydrothermal (Co-UH) methods, and their physicochemical properties were characterised by numerous techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption of O2 (O2-TPD), and temperature-programmed desorption of NH3 (NH3-TPD). The catalytic activity of each catalyst was estimated for the catalytic combustion of vinyl chloride (VC) emissions. The crystallite size of the Co3O4 catalyst was found to be well correlated with the amounts of surface-adsorbed oxygen species and number of acid sites on the catalyst surface, and consequently, determined several physicochemical properties of the catalyst. Of the catalysts studied here, the Co-AP catalyst exhibits the smallest crystallite size, which increases the specific surface area and the concentration of Co2+ on the catalyst surface. This, in turn, enhances the redox property, oxygen mobility, and the number of acid sites associated with the Co-AP catalyst. In fact, the Co-AP catalyst exhibits the best catalytic activity for VC combustion at 360 °C and does not produce any chlorinated by-products.

Mechanism of CeO2 synthesized by thermal decomposition of Ce-MOF and its performance of benzene catalytic combustion

In this paper, the formation mechanism of mesoporous CeO2 synthesized by thermal decomposition of Ce-MOF and its performance of benzene catalytic combustion, as well as the structure–activity relationship between them were studied in depth. The self-assembly process and physicochemical properties of CeO2 were characterized by thermogravimetry analysis, powder X-ray diffraction, N2 adsorption/desorption, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy techniques. Characterization results show that Ce-MOF is completely decomposed into pure mesoporous CeO2 when the decomposition temperature is higher than 400 °C. At this threshold temperature, CeO2 (400) has the largest specific surface area and pore volume of 114 m2/g and 0.152 cm3/g, respectively. CeO2 (400) exhibits very high catalytic activity for benzene combustion, which can completely catalyze the degradation of benzene at 260 °C. Meanwhile, the mesoporous CeO2 (400) supported Pt nanocrystalline catalysts were prepared by high temperature solution-phase reduction method. Pt/CeO2 (400) can completely degrade benzene at about 200 °C and represents high durability and good water-resistance for benzene combustion during 100 h of continuous reaction.

Microfibrous structured Au/Co3O4/Al-fiber catalyst for the combustion of ethylene traces

Microfibrous structured Au/Co3O4/Al-fiber catalyst to be used for the combustion of ethylene (C2H4) traces was developed by hydrothermal growth of Co(OH)2 nanoarrays onto thin-sheets of Al-fiber followed by solvent-assisted incipient wetness impregnation of Au NPs. Such catalyst supported on the Co(OH)2/Al-fiber nanoarrays with different morphology exhibits different C2H4 conversion under the same combustion reaction conditions. Notably, the Au/Co3O4/Al-100 of low Au content provides unique combination of high low-temperature activity and high throughput. It was found that the strong Au-Co3O4 interactions over the Au/Co3O4/Al-100 catalyst prepared at 100 °C under hydrothermal conditions facilitate oxygen adsorption and activation, thereby enhancing the low-temperature catalytic activity for ethylene combustion.

Direct Synthesis of Novel Sponge-Like Porous MnOx Catalysts Derived from Mn-MOFs for High-Efficiently Eliminate o-Dichlorobenzene by Catalytic Combustion

A series of novel lamellar sponge-like MnOx porous catalysts derived from Mn-MOFs have been prepared via modulator-assisted synthesis method and their catalytic performance has been evaluated for o-dichlorobenzene (o-DCB) catalytic combustion reaction. The catalysts were characterized by BET, XRD, Raman, SEM, TEM, XPS, H2-TPR, O2-TPD and other techniques to test the physicochemical properties of the catalysts. The results showed that MnOx had different morphology and properties. The active oxygen species and large specific surface area of MnOx played an important role in the catalytic combustion of o-dichlorobenzene. The T90 of the laminar catalyst MnOx-D, MnOx-D/M, MnOx-D/H/M, and MnOx-D/H was 321, 341, 346, and 355 °C, respectively. MnOx-D has good catalytic activity for the catalytic combustion of o-DCB, which confirmed that surface lattice oxygen played a crucial role in o-DCB combustion. Additionally, they had good hydrothermal stability, thermal stability and water resistance.

Study of the use of a Pd–Pt-based catalyst for the catalytic combustion of storage tank VOCs

Catalytic combustion is a very cost-effective way to eliminate volatile organic compounds (VOCs). The components of the VOCs in storage tanks are complex, with alkanes, alkenes and aromatic hydrocarbons being the main components. The aromatic hydrocarbons are the most difficult organic compounds among the storage tank VOCs in terms of catalysing combustion, and they are easy to cause catalyst carbon deposition. In this work, the Pt/γ-Al2O3, Pd/γ-Al2O3, Pd–Pt/γ-Al2O3, Pd–Pt/CeO2/γ-Al2O3 and Pd–Pt/CeO2/γ-Al2O3–N catalysts were prepared using an incipient wetness impregnation method. The performances of the catalysts were investigated using toluene and a simulation of VOCs in gas in a storage tank as model reactants. The study found that Pt has a higher catalytic combustion activity than Pd for the alkanes in the VOC gas in the simulation storage tank, and Pd has a higher catalytic combustion activity than Pt for the alkenes and toluene in the VOC gas in the simulation storage tank. The Pt addition enhances the activity of Pd-based catalysts for VOC catalytic combustion, and the Pd–Pt active component has good active stability. The catalyst prepared by using Pd–Pt alone has a defect in that it exhibits an insufficient oxygen supply performance in the catalytic combustion process. The addition of CeO2 improves the oxygen supply performance of the Pd–Pt-based catalyst. In addition, the activity of the Pd–Pt/CeO2/γ-Al2O3–N catalyst prepared by reducing the validated amount of Pd–Pt is higher than that of a commercial catalyst.

Enhanced Catalytic Activity for Methane Combustion through in Situ Water Sorption

Although palladium-based materials are efficient catalysts for methane combustion, H2O-poisoning remains a significant problem at low operating temperatures (<450 °C). It is a significant research ...

CuO/MnOx composites obtained from Mn-MIL-100 precursors as efficient catalysts for the catalytic combustion of chlorobenzene

A series of CuO/MnOx composites has been synthesized by integrating the incipient wetness impregnation method and the heat treatment of Mn-MIL-100. The catalytic activity has been tested by chlorobenzene (CB) degradation. The obtained catalysts were characterized by XRD, Raman, TG, TEM, XPS, N2 adsorption–desorption, H2-TPR and TPSR-MS. The results revealed that the catalytic activity of MnOx improved remarkably after loading Cu, particularly the catalyst with 30 wt.% CuO (30Cu/MnOx) exhibited the best catalytic activity in CB combustion, whose T90% was 290 °C at GHSV of 15,000 h−1. The excellent catalytic performance of 30Cu/MnOx could be attributed to the abundant mesoporous structure, improved reducibility, surface-enriched Mn4+ species and active adsorbed oxygen species. Moreover, the TPSR-MS data showed that 30Cu/MnOx exhibited higher dechlorination ability and better resistance to chlorine poisoning during CB degradation process. This study may provide a new strategy for developing mixed metal oxides derived from MOF serving as high-performance catalysts in the catalytic combustion removal of VOCs.

Electrochemical promotion of propane oxidation at Pt/BiCuVOx-YSZ thin-film cells: Economical use of YSZ

Abstract Electrochemical promotion of catalysis (EPOC) or Non-faradaic electrochemical modification of catalytic activity (NEMCA) is a phenomenon that may be exploited in catalytic converters to reduce the usage of precious metal catalysts. Nevertheless, the conventional structure of NEMCA cells employs a thick piece of relatively expensive solid electrolyte such as yttria-stabilised zirconia (YSZ). Minimising the amount of this costly material may bring EPOC closer to commercial application. NEMCA cells were fabricated with thin films of YSZ or BiCuVOx-YSZ as the electrolytes and sputtered Pt as the working catalyst electrodes. The catalytic activity for propane combustion was studied at 200, 300, 400, and 500 °C for cells with YSZ, but only at 400 °C for cells with BiCuVOx-YSZ. The effects of working electrode potentials and BiCuVOx contents were also studied. Most cells made with only YSZ could not function as electrochemical cells. Nevertheless, only one cell survived and exhibited NEMCA. On the other hand, all BiCuVOx-YSZ cells functioned properly. Electrophobic NEMCA behaviour was observed from both cell types. Addition of BiCuVOx improved sintering and resulted in films of higher conductivity. Nonetheless, diminished surface areas and suppressed faradaic efficiencies were observed. Undesirable electronic conductivity was also introduced by BiCuVOx and hence an optimum BiCuVOx content of 3.5 wt % was observed to offer the highest rate enhancement ratio, ρ, and the highest faradaic efficiency, Λ, of 5.3 and 339, respectively, at 400 °C.

High-efficient non-noble metal catalysts of 3D ordered macroporous perovskite-type La2NiB’O6 for soot combustion: Insight into the synergistic effect of binary Ni and B’ sites

Double perovskite-type La2NiB’O6 (B’=Mn, Fe, Co, Cu) catalysts with three-dimensional ordered macroporous (3DOM) structure were synthesized by colloidal crystal template method. 3DOM structure promotes the contact efficiency between soot and catalyst. The periodic arrangement of [NiO6] and [B’O6] octahedrons in La2NiB’O6 induces the formation of coordination unsaturated B-site ions. 3DOM La2NiB’O6 catalysts exhibited super catalytic performance for soot combustion under the simulated exhaust, and their catalytic performances are dependent on the synergistic effect of binary Ni and B'-site ions. 3DOM La2NiCoO6 catalyst had the highest catalytic activity for soot combustion, i.e., its T50, SCO2m, TONs and TOFOv values are 362 °C, 98.2 %, 7.80 and 0.151 h−1, respectively. The mechanism was proposed that the synergistic effect of Ni and B’ ions boosts the key step of NO oxidation to NO2. It is meaningful for the development of the non-precious metal catalysts during soot combustion.

Pt-loaded ellipsoidal nanozeolite as an active catalyst for toluene catalytic combustion

Abstract In this study, the Pt-loaded ellipsoidal nanozeolite (Pt/ZSM-5-OS) was successfully synthesized by the mercaptosilane modification assisted Pt dispersion method and investigated for the catalytic combustion of toluene, which was used as a model compound of volatile organic compounds (VOCs). The catalytic activity evaluation showed that Pt/ZSM-5-OS exhibited an excellent activity in toluene catalytic combustion, with 90% conversion (T90) occurring at just 164 °C. The catalytic activity was much higher than the catalyst prepared by traditional impregnation method (Pt/ZSM-5-IM, T90 = 196 °C). In addition, the excellent properties of anti-water vapor and catalytic stability were observed for Pt/ZEM-5-OS. The as-prepared catalysts were characterized by X-ray diffraction (XRD), N2 physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Characterization of the as-prepared catalysts demonstrated that the enhanced catalytic performance was related to the improved Pt dispersion and higher Pt0 proportion of Pt-ZSM-5-OS. Hence, Pt/ZSM-5-OS and its preparation method are attractive for the practical VOCs catalytic combustion.