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CuO/CeO2 catalysts were widely studied as an alternative to precious metal catalysts, and the Cu–Ce synergy was essential to improve the catalytic performance. In this paper, the effects of CuO loading on Cu–Ce synergy in CuO/CeO2 nanorod catalysts and their performance in toluene combustion were systematically investigated. It was found that non-equilibrium plasma facilitated the dispersion of CuO active species on the CeO2 surface. With the increase of the CuO loading from 1 wt% to 4 wt%, the Cu–Ce synergistic effect was gradually improved, which generated Cu+/Cu2+ and Ce3+/Ce4+ redox electron pairs. The highest oxygen vacancy concentration and Cu+ content of CuCe-4 (4 wt%) resulting from strong Cu–Ce synergy accelerated the activation of chemisorbed oxygen and consequently improved the efficiency of toluene catalytic combustion. [ABSTRACT FROM AUTHOR]

CO self-sustaining combustion, induced by a CuCe0.75Zr0.25Oy catalyst, has been confirmed experimentally as an effective strategy to reduce serious environmental pollution and energy waste, which is caused by direct combustion of conventional converter gas in the steelmaking industry. In this paper, the effects of CuCe0.75Zr0.25Oy catalysts prepared by a sol-gel method via three different pore-forming agents (oxalic acid, cellulose and thermal decomposition) were investigated for their catalytic activity of self-sustained CO combustion. Additionally, characterization methods were used to obtain the structural properties of each catalyst. The results obtained show that the CuCe0.75Zr0.25Oy catalyst, as a sol-gel pore-forming agent, prepared from cellulose exhibits the highest activity among the three catalysts. Under the condition of a reaction gas (3% CO+5% O2/N2), the T10 (70°C), T50 (73°C) and T90 (78°C) of the cellulose catalyst are obviously lower than those of the other catalysts, where T10, T50 and T90 denote the reaction temperature corresponding to the CO conversion of 10%, 50% and 90%, respectively. The reason is that the cellulose pore-forming agent promotes the formation of a multistage porous structure, which strengthens the synergistic effect between the Cu and Ce catalysts and changes the redox property of the overall catalyst. On the one hand, the strong synergy between CuO and CeO2 adjusts the dispersion and chemical state of copper nanoparticles. On the other hand, the oxygen vacancies generated locate at the copper-cerium interface enhance the ability of oxygen storage and oxygen release of the catalyst. [ABSTRACT FROM AUTHOR]

The Cu/ZSM-5, Ce/ZSM-5 and Cu-Ce/ZSM-5 catalysts were prepared and characterized in this investigation and the catalytic activity of carbon monoxide (CO) combustion under these catalysts was determined by temperature-programmed oxidation. The activity for the CO combustion follows the decreasing order: Cu-Ce/ZSM-5 > Cu/ZSM-5 > Ce/ZSM-5, indicated by lower ignition, light-off, extinction temperature and broader hysteresis determined via both heating and cooling feeding process. The CO adsorbed on the copper sites to form Cu + –CO complexes, monodentate and bidentate carbonates was considered to be the crucial step for CO catalytic combustion. At the CO concentration ≥5 vol.%, the CO self-sustained combustion was achieved over the Cu-Ce/ZSM-5 catalyst. One reason is due to formation of Cu 2+ ions incorporated into cerium oxides, which are more reducible than the copper clusters, minicrystals and bulk CuO particles. Another reason is attributable to the formation of Ce 4+ /Ce 3+ redox couple, which facilitates oxygen transport on the catalyst surface. [ABSTRACT FROM AUTHOR]

Abstract: Zirconium doped Cu/ZSM-5 catalysts were prepared and characterized in this investigation. Catalytic activity during soot combustion was determined in both O2/He and NO/O2/He atmospheres by temperature-programmed oxidation. The use of zirconium reduces the temperature of maximum soot oxidation rate by 229°C in O2/He atmosphere and 270°C in NO/O2/He atmosphere. The promoting effect of zirconium is discussed in terms of surface dispersion, enrichment of active components, and creation of oxygen vacancies where molecular oxygen or NO x is adsorbed forming basic surface oxygen species active for soot oxidation. The NO2 formed at the copper–zirconium interface sites leads to the ignition temperature being significantly decreased to 93°C, which is inside the exhaust temperature range of diesel engines. To understand the combustion reaction kinetics, the activation energy and reaction order of soot combustion were evaluated. According to the Redhead method, the activation energy for non-catalyzed reaction is 164kJ/mol under the O2/He atmosphere. For the Cu/ZSM-5 and Cu–Zr/ZSM-5, the activation energies under the O2/He atmosphere (134–151kJ/mol) are slightly higher than those under the NO/O2/He atmosphere (128–135kJ/mol). The Freeman–Carroll method is suitable to describe the soot combustion in the NO/O2/He atmosphere, with the activation energies for the catalysts in the range of 97–112kJ/mol and the average value of reaction order equal to 1.36. [Copyright &y& Elsevier]

The oxidation rates of diesel soot from the combustion chamber of a running diesel engine were calculated based on the particle size distributions at different crank angles. The primary particle diameter and nanostructure of soot were obtained by means of high-resolution transmission electron microscopy (HRTEM). The soot characteristics were also investigated by oxidative thermogravimetry and Raman scattering spectrometry. The results showed the soot nanostructures were dependent on engine operation conditions and combustion phases. The oxidation rates were found to differ by nearly fourfold from that calculated by the Nagle/Strickland-Constable (NSC) model for the soots studied here. The varied oxidation rates were interpreted in terms of differences in nanostructure between the soots. The experimental results were used to modify the NSC model and the fringe length of in-cylinder diesel soot was chosen to describe the influence of graphitisation on the oxidation of soot. The modified NSC model lessened the deviation between measurements and predictions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The L-H mechanism dominates the low-temperature induction stage. • Coexistence of M−K and L-H mechanisms in ammonia catalytic combustion. • (M−K) /(L-H) = 0.427 (Induction stage) and 0.627 (continuous combustion stage). • The NH and NH 2 are the key species for the two stages of N 2 production (i-SCR). • The CuO-CeO 2 achieves self-sustained catalytic combustion at NH 3 = 14%. Carbon-free hydrogen-rich ammonia (NH 3) is a potential next energy generation source, where a high ignition point and high nitric oxide contents, thereby limiting further development. This study aims to investigate the mechanism evolution during the catalytic ignition process of high NH 3 concentration over copper-cerium catalyst to address the demerits of flame combustion. The phase composition, elemental valence, and active species of the copper-cerium oxide (CuO-CeO 2) catalyst are investigated using various characterization techniques. The results indicated that Cu species are mainly present in copper-cerium solid solutions and highly dispersed CuO clusters, providing sufficient Cu sites to adsorb NH 3 and abundant reactive lattice oxygen. The catalytic ignition triggered a kinetic transition from low-rate to high-rate steady-state. During the induction process, the predominance of the L-H mechanism is implied by the kinetic modeling and transient experiments (low-rate induced phase). Combined with IR spectroscopy and isotope (18O 2)-transient response study, the results indicated that adsorbed NH 3 reacted with surface adsorbed oxygen, simultaneously pulling out lattice oxygen to react with adsorbed NH 3 , confirming the coexistence of L-H and M−K mechanism over CuO-CeO 2. The L-H mechanism (18O, contribution of adsorbed oxygen) plays a relatively dominant role in the induction stage, while the involvement of the M−K mechanism (16O, contribution of lattice oxygen) is significantly increased in the sustained combustion stage. At both stages, NH and NH 2 served as critical species for N 2 generation (i-SCR), respectively, playing an important role in N 2 selectivity. Moreover, in the self-sustained combustion stage for CuO-CeO 2 (14%NH 3), the rapid gas diffusion and mass transfer facilitated the adsorption and activation of NH 3. These results are envisaged to provide theoretical support for the handling and application of high concentrations of NH 3. [ABSTRACT FROM AUTHOR]

CO self-sustaining catalytic combustion tends to be one of potential means to achieve efficient conversion of off-gases from steelmaking. Building model catalysts to investigate the reaction process academically is essential to design optimized catalysts and Cu 2 O exposing (1 0 0), (1 1 1) and (1 1 0) planes are excellent materials. Herein, morphological CeO 2 /Cu 2 O inverse model catalysts were synthesized to reveal the synergistic effect and reaction mechanism. It is demonstrated that the ignition temperature is lowered on the interface by synergistic effect, which dominates the ignition, while the combustion after ignition is controlled by Cu 2 O planes providing abundant lattice oxygen to react with CO. Additionally, exposure of different planes plays a significant role in the reaction since O-termination on (1 0 0) inhibits the interaction, whereas Cu-termination on (1 1 0) surface structure and coordinately unsaturated Cu+ on open (1 1 1) surface respectively contribute to their superior catalytic performance. [Display omitted] ● Inverse model CeO 2 /Cu 2 O catalysts with regular morphology were successfully prepared. ● Synergistic effect on Cu-Ce interface lowered ignition temperature, dominating the ignition. ● The catalytic activity and synergistic effect vary among planes with (1 1 1) performing the best. ● Exposure of crystal planes with higher activity assists in designing optimized catalysts. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The catalytic self-sustained combustion of toluene was successfully developed. • CuCeZr/TiO 2 catalyst showed the excellent performance in self-sustained combustion. • TPO in N 2 atmosphere was used to investigate the role of lattice oxygen in toluene combustion. Abstract The catalytic self-sustained combustion of toluene over Cu x Mn 1-x Ce 0.75 Zr 0.25 /TiO 2 catalysts (x = 1, 0.5, 0) was studied in a microscale combustor. The catalytic activity is determined not only by the temperature with toluene conversion of 90% (T co), but also by the corresponding lean-combustion limits. It was found that the self-sustained combustion was achieved successfully over the catalysts, with the toluene concentrations of 0.35 con.%, 0.50 con.% and 1.00 con.%. According to T co, the activity decreased in the order of CuCe 0.75 Zr 0.25 /TiO 2 (234 °C)＞Cu 0.5 Mn 0.5 Ce 0.75 Zr 0.25 /TiO 2 (238 °C) ＞MnCe 0.75 Zr 0.25 /TiO 2 (284 °C). The excellent activity of CuCe 0.75 Zr 0.25 /TiO 2 catalyst could be ascribed to the high content of active lattice oxygen, good low-temperature reducibility and homogeneous dispersion, combined with the results of H 2 -TPR, O 2 -TPD and XPS. Furthermore, the results of in-situ DRIFT and temperature-programmed oxidation (TPO) of toluene in N 2 atmosphere suggested that toluene was adsorbed on the catalyst surface by removing α-H from methyl and combining with active oxygen specie to form benzyl group, which was finally oxidized into CO 2 and H 2 O with lattice oxygen. [ABSTRACT FROM AUTHOR]

Self-sustained catalytic combustion is a sustainable approach to deal with exhaust gas with high concentration CO, and revealing its reaction process is necessary and challenging. Herein, cube (Cu 2 O-C), octahedron (Cu 2 O-O) and dodecahedron (Cu 2 O-D) exposing different crystal planes were used to explore the catalytic combustion mechanism. The catalytic combustion can be self-sustained on the Cu 2 O surface and the activities decrease in the order of Cu 2 O-O > Cu 2 O-D > Cu 2 O-C, contributing to the different exposing planes with (1 1 1), (1 1 0) and (1 0 0), respectively. In-situ DRIFTS results prove that the catalytic combustion of CO to CO 2 on Cu 2 O is prone to follow the MvK mechanism. Comparing with Cu 2 O-D and Cu 2 O-C, the relatively open surface of Cu 2 O-O plane composed of unsaturated copper and oxygen atoms facilitates the CO adsorption on Cu (I) and the mobility of lattice oxygen, leading to the highest low temperature reducibility and catalytic activity. [Display omitted] • CO self-sustained catalytic combustion were achieved on cube, octahedron and dodecahedron Cu 2 O. • Octahedron Cu 2 O with (1 1 1) planes exhibits the best activity for high concentration CO. • Coordination unsaturated Cu and O on the (111) and (110) planes promote CO oxidation. • Catalytic combustion reaction of CO on Cu 2 O mainly follows the MvK mechanism. [ABSTRACT FROM AUTHOR]

Cubic Cu 2 O micro/nanocrystals were successfully synthesized by liquid-phase reduction using copper salt of CuSO 4 or CuCl 2 ·2H 2 O, and glucose or ascorbic acid as reducing agent, respectively. The activity of the catalysts was evaluated by light-off curves of CO self-sustained catalytic combustion via temperature-programmed oxidation of CO (CO-TPO), with the results showing the activity of catalysts following the order of Cu 2 O–Cl-GLU > Cu 2 O– S -GLU > Cu 2 O– S -AA > Cu 2 O–Cl-AA, (Cl denotes CuCl 2 ·2H 2 O, GLU denotes glucose, S denotes CuSO 4 and AA denotes ascorbic acid, respectively), corresponding to the ignition temperature of 109 °C, 122 °C, 137 °C and 186 °C, respectively. The crystal structure, elemental valence, morphology and redox property of the prepared catalysts were analyzed by using various characterization techniques. Combined with in situ infrared spectrum, the CO self-sustained catalytic combustion over Cu 2 O catalysts mainly follows the Mars-van-Krevelen (M-v-K) mechanism: the adsorbed and activated CO reacts with lattice oxygen to yield CO 2 and oxygen vacancy, and then the oxygen vacancy can be replenished by gaseous oxygen. Combined with catalytic performance of high-concentration CO, it is found that the catalysts prepared using glucose as reducing agent are more angular compared with ascorbic acid. The Cu 2 O–Cl-GLU synthesized with glucose and CuCl 2 ·2H 2 O exhibits the best catalytic activity among all the catalysts tested, attributing to its more obvious edge and rough crystal surface. The unique structure of Cu 2 O–Cl-GLU leads to the high exposure rate and coordination unsaturation of atoms on the cubic Cu 2 O micro/nanocrystals that can improve the ability of activating gaseous O 2 and low temperature reducibility, and consequently facilitating the catalytic activity. Cycle path diagram of CO oxidation reaction (a) and schematic diagram of CO oxidation reaction on Cu 2 O (b). [Display omitted] • Effects of reducing agent on catalytic properties is greater than that of copper salt. • High concentration CO can achieve self-sustained catalytic combustion on obtained Cu 2 O. • Glucose enhances unsaturation of Cu atoms contributing to high activity. • Chemically adsorbed oxygen on Cu 2 O surface promotes CO ignition. [ABSTRACT FROM AUTHOR]

• The LMO-W, LMO-SW, LCMO-W, LCMO-SW, LSMO-W and LSMO-SW catalysts were well designed by precursors. • The Binary search was used to determine the lean-combustion limits for the self-sustained combustion of CO. • The stability of the LCMO-SW catalyst was evaluated under CO oxidation at the furnace temperature of 535 °C. • The influence mechanism of self-sustaining combustion stability of CO catalyst was investigated and put forward. • The L-H mechanisms were performed for SCR reaction over the catalysts via in situ IR experiments. The LaMnO 3 , La 0.9 Ce 0.1 MnO 3 and La 0.9 Sr 0.1 MnO 3 catalysts are synthesized using sugar agent, and the CO self-sustained combustion is investigated, where the catalytic performance is decided by temperature with CO conversions of 10% (T 10), 50% (T 50), and 90% (T 90). The results show that self-sustaining combustion is successfully realized on the catalyst, and the order of activity decrease is as follows: La 0.9 Ce 0.1 MnO 3 (with sugar) > La 0.9 Sr 0.1 MnO 3 (with sugar) > LaMnO 3 (with sugar) > LaMnO 3 (without sugar) > La 0.9 Sr 0.1 MnO 3 (without sugar) > La 0.9 Ce 0.1 MnO 3 (without sugar). Combined with the results of XPS, H 2 -TPR, O 2 -TPD and CO-TPD techniques, the excellent activity of La 0.9 Ce 0.1 MnO 3 (with sugar) can be attributed to the high content of Mn4+ ions and reactive oxygen vacancies enriched on the catalyst surface, sound low-temperature reduction, and uniform dispersion. Besides, in situ IR spectroscopy results indicate that the catalytic combustion of CO over manganese-based perovskite catalysts follows the L-H mechanism: the chemisorption of CO and O 2 takes place to produce monodentate carbonates and bicarbonate species, which then decompose to yield CO 2 release. The high-temperature stability test provides evidence that the La 0.9 Ce 0.1 MnO 3 (with sugar) gives 100% CO conversion and that the activities remain almost unchanged after reaction for 12 h, where the temperature of catalyst bed reaches about 717 °C. The results obtained are helpful to accept this technology on efficient and clean energy utilization in iron and steel industry. [ABSTRACT FROM AUTHOR]

The reaction pathways of CO oxidation over the (1 0 0), (1 1 0) and (1 1 1) crystal planes of Cu 2 O. • Morphologies of Cu 2 O micro/nanocrystals were controlled by simply changing precursor concentration. • Increase of precursor concentration results in more exposure of active crystal plane of Cu 2 O. • Activity of CO self-sustained catalytic combustion on Cu 2 O increases with precursor concentration. • Coordination unsaturated Cu and O on the (1 1 1) and (1 1 0) planes promote CO oxidation. The self-sustained catalytic combustion is one of the most effective ways to remove high concentration CO at low temperature. In this paper, Cu 2 O micro/nanocrystals with different morphologies were successfully synthesized by changing the precursor concentration using liquid phase reduction method. The obtained Cu 2 O were characterized using SEM, XRD, XPS, H 2 -TPR and O 2 -TPD, and the relationship between the catalytic performance and morphology was analyzed based on CO-TPD-MS and activity evaluation results. It was found that high precursor concentration leads to more exposure of active crystal planes of Cu 2 O. Compared with Cu 2 O-1 exposing only (1 0 0) crystal planes, Cu 2 O-5, the precursor concentration of which is 5 times of Cu 2 O-1, exposes (1 0 0) and (1 1 0) crystal planes. Cu 2 O-9, with 9 times of precursor concentration of Cu 2 O-1, exposes (1 0 0), (1 1 0) and (1 1 1) crystal planes simultaneously. All the obtained Cu 2 O with different precursor concentrations can achieve self-sustained CO catalytic combustion, and the catalytic activity increases with increasing precursor concentration (Cu 2 O-1 < Cu 2 O-5 < Cu 2 O-9). The results prove that unsaturated coordination of Cu and O on the (1 1 1) and (1 1 0) planes can enhance the corresponding reducibility, adsorption and activation of gaseous oxygen, consequently promoting the CO oxidation to CO 2 over Cu 2 O-9. [ABSTRACT FROM AUTHOR]

• The powder sample is well designed and coated on the HC tube to form CuCe 0.75 Zr 0.25 O δ /HC catalyst. • The transient changes and two-dimensional temperature region are obtained for CO self-combustion via CO-TPO + FLIR. • The various intermediate species and competitive adsorption of reactants on different active sites are evidenced. • The different pathways and roles of M-K and L-H mechanisms are proposed using in situ IR. A CuCe 0.75 Zr 0.25 O δ catalyst was prepared by the sol-gel method and successfully coated on honeycomb ceramic (HC) carrier. The activity of CuCe 0.75 Zr 0.25 O δ /HC was determined by the CO-TPO + FLIR, with the results performing that the critical condition for CO self-sustained combustion is 3 vol% CO + 3 vol% O 2 /N 2 at 0.5 L/min. As the CO concentration increases from 1 vol% CO to 3 vol% CO, the induction process (T 15) shifts to rapid ignition with a transient change for the CO oxidation reaction. The furnace temperature for CO self-sustained combustion decreases with increasing the CO and O 2 concentrations. Upon increasing the CO 2 concentration, however, furnace temperature is needed to increase and realize CO complete conversion. The thermal stability test combined with SEM + EDX results indicate that the CuCe 0.75 Zr 0.25 O δ /HC retains an excellent thermal stability after a 200 h, and the high-temperature region remains at 225 ± 1 °C during the CO self-combustion reaction. The activity of catalyst is reduced slightly after the 200 h test because of the carbon deposition on the catalyst surface, but such a slight deactivation can be eliminated by the air oxidation method. In situ IR results show a competitive adsorption of CO/O 2 and CO 2 on the Cu-Ce active sites, indicating that the addition of gaseous CO 2 performs an inhibition of CO oxidation. CO preferentially adsorbs linearly at Cu+ sites to form carbonyls that react with lattice oxygen to produce CO 2 to release, which can be ascribed to M-K mechanism. The L-H mechanism is less important, which involves the relatively weak reaction of adsorbed CO and adsorbed oxygen on the Cu-Ce active sites to form carbonate species. [ABSTRACT FROM AUTHOR]