Transient behavior and reaction mechanism of CO catalytic ignition over a CuO–CeO2 mixed oxide

As a key heterogeneous process, the catalytic oxidation of CO is essential not only for practical applications such as automotive exhaust purification and fuel cells but also as a model reaction to study the reaction mechanism and structure-reactivity correlation of catalysts. In this study, the variation in activity-controlling factors during CO catalytic ignition over a CuO-CeO 2 catalyst was investigated. The activity for CO combustion follows the decreasing order of CuO-CeO 2 > CuO > CeO 2. Except for inactive CeO 2, increasing temperature induces CO ignition to achieve self-sustained combustion over CuO and CuO-CeO 2. However, CuO provides enough copper sites to adsorb CO, and abundant active lattice oxygen, thus obtaining a higher hot zone temperature (208.3 °C) than that of CuO-CeO 2 (197.3 °C). Catalytic ignition triggers a kinetic transition from the low-rate steady-state regime to a high-rate steady-state regime. During the induction process, Raman, X-ray photoelectron spectroscopy, CO temperature-programmed desorption and IR spectroscopy results indicated that CO is preferentially adsorbed on oxygen vacancies (Cu +-[Ov]-Ce 3+) to yield Cu +-[C≡O]-Ce 3+ complexes. Because of the self-poisoning of CO, the adsorbed CO and traces of adsorbed oxygen react at a relative rate, which is entirely governed by the kinetics on the CO-covered surface and the heat transport until the pre-ignition regime. The Cu +-[C≡O]-Ce 3+ complex is a major contributor to CO ignition. The step-response runs and kinetic models showed that after ignition, a kinetic phase transition occurs from a CO-covered surface to an active lattice oxygen-covered surface. During CO self-sustained combustion, the rapid gas diffusivity and mass transfer is beneficial for handling the low coverage of CO. The active lattice oxygen of CuO takes part in CO oxidation

Synthesis of Cu2O micro/nanocrystals for catalytic combustion of high-concentration CO: The crucial role of glucose

Cubic Cu2O micro/nanocrystals were successfully synthesized by liquid-phase reduction using copper salt of CuSO4 or CuCl2.2H2O, 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 Cu2O-ClGLU > Cu2O-S-GLU > Cu2O-S-AA > Cu2O-Cl-AA, (Cl denotes CuCl2.2H2O, GLU denotes glucose, S denotes CuSO4 and AA denotes ascorbic acid, respectively), corresponding to the ignition temperature of 109 degrees C, 122 degrees C, 137 degrees C and 186 degrees 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 Cu2O catalysts mainly follows the Mars-van-Krevelen (M-v-K) mechanism: the adsorbed and activated CO reacts with lattice oxygen to yield CO2 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 Cu2O-Cl-GLU synthesized with glucose and CuCl2.2H2O exhibits the best catalytic activity among all the catalysts tested, attributing to its more obvious edge and rough crystal surface. The unique structure of Cu2O-Cl-GLU leads to the high exposure rate and coordination unsaturation of atoms on the cubic Cu2O micro/nanocrystals that can improve the ability of activating gaseous O2 and low temperature reducibility, and consequently facilitating the catalytic activity

Self-sustained combustion of CO with transient changes and reaction mechanism over CuCe0.75Zr0.25O delta powder for honeycomb ceramic catalyst

A CuCe0.75Zr0.25O delta catalyst was prepared by the sol-gel method and successfully coated on honeycomb ceramic (HC) carrier. The activity of CuCe0.75Zr0.25O delta/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 CO2 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 CuCe0.75Zr0.25O delta/HC retains an excellent thermal stability after a 200 h, and the high-temperature region remains at 225 +/- 1 degrees 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 CO2 on the Cu-Ce active sites, indicating that the addition of gaseous CO2 performs an inhibition of CO oxidation. CO preferentially adsorbs linearly at Cu+ sites to form carbonyls that react with lattice oxygen to produce CO2 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

Effects of precursor concentration on morphologies of Cu2O micro/nanocrystals and properties of CO self-sustained catalytic combustion

The self-sustained catalytic combustion is one of the most effective ways to remove high concentration CO at low temperature. In this paper, Cu2O micro/nanocrystals with different morphologies were successfully synthesized by changing the precursor concentration using liquid phase reduction method. The obtained Cu2O 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 Cu2O. Compared with Cu2O-1 exposing only (100) crystal planes, Cu2O-5, the precursor concentration of which is 5 times of Cu2O-1, exposes (100) and (110) crystal planes. Cu2O-9, with 9 times of precursor concentration of Cu2O-1, exposes (100), (110) and (1 1 1) crystal planes simultaneously. All the obtained Cu2O with different precursor concentrations can achieve self-sustained CO catalytic combustion, and the catalytic activity increases with increasing precursor concentration (Cu2O-1 < Cu2O-5 < Cu2O-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 CO2 over Cu2O-9

Effects of Cu2O morphology on the performance of CO self-sustained catalytic combustion

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 (Cu2O-C), octahedron (Cu2O-O) and dodecahedron (Cu2O-D) exposing different crystal planes were used to explore the catalytic combustion mechanism. The catalytic combustion can be self-sustained on the Cu2O surface and the activities decrease in the order of Cu2O-O > Cu2O-D > Cu2O-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 CO2 on Cu2O is prone to follow the MvK mechanism. Comparing with Cu2O-D and Cu2O-C, the relatively open surface of Cu2O-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

Study on the Dip Angle Effect of Asymmetric Deformation and Failure of the Gob-Side Coal–Rock Roadway in Gently Inclined Coal Seam

In order to reveal the influence law of coal seam dip angle on the stability of the surrounding rock of the gob-side coal–rock roadway in a gently inclined coal seam (GCRGICS), the deformation characteristics of the surrounding rock under four different coal seam dip angles of this kind of roadway were studied by field investigation, theoretical analysis and numerical simulation. The results showed that, with the increase of the coal seam dip angle, the amount of the roadway roof subsidence and the deformation of the upper and lower side arc triangle coal along the coal–rock interface increased, and the maximum deformation was 479 and 950 mm, respectively, and the maximum slip deformation area gradually shifted from the upper side arc triangle coal to the lower side arc triangle coal. The asymmetric deformation characteristics of the surrounding rock became more and more obvious. The asymmetric deformation rate of the GCRGICS showed a V-shaped variation relationship with the coal seam dip angle, when the coal seam dip angle was 10°, the asymmetric deformation rate was the minimum, only 1.1%. The plastic zone of the surrounding rock expanded with the increase of the coal seam dip angle, and the new extension range was mainly located in the roof area of the roadway

Investigation of the Bearing Characteristics of Bolts on a Coal–Rock Combined Anchor Body under Different Pull-Out Rates

In order to reveal the influence of the pull-out rate on the load-bearing properties of the coal–rock combined anchor body, the mechanical properties and failure characteristics of a coal–rock combined anchor body under different pull-out rates (10, 20, 30, 40, 50 mm/min) were studied using the pull-out test and theoretical analysis. The results show that the bearing capacity of the bolt on the coal–rock combined anchor body improves under a dynamic load, but the load-bearing properties of the coal–rock combined anchor body are different from those of the full rock (coal) anchor body. With the increase in the pull-out rate, the maximum pull-out load of the bolt on the coal–rock combined anchor body increases first, then decreases, and finally tends to be stable. Under the condition of a low drawing rate, the bearing capacity of the coal–rock combined anchor system can be greatly improved, but when the pull-out rate exceeds 20 mm/min, the bearing capacity of the anchor system is reduced. The debonding process of the anchoring section of the coal–rock combined anchor body gradually expands from the beginning section of the anchor to the bottom of the borehole. The coal–rock combined anchor body undergoes time differential development of cracks, and the failure of the coal and rock mass occurs at different times. Its failure process can be divided into three stages: (1) the coal anchor and rock anchor act together; (2) the rock anchor acts alone; and (3) the coal anchor and rock anchor have residual action

Investigation of the Bearing Characteristics of Bolts on a Coal&ndash;Rock Combined Anchor Body under Different Pull-Out Rates

In order to reveal the influence of the pull-out rate on the load-bearing properties of the coal&ndash;rock combined anchor body, the mechanical properties and failure characteristics of a coal&ndash;rock combined anchor body under different pull-out rates (10, 20, 30, 40, 50 mm/min) were studied using the pull-out test and theoretical analysis. The results show that the bearing capacity of the bolt on the coal&ndash;rock combined anchor body improves under a dynamic load, but the load-bearing properties of the coal&ndash;rock combined anchor body are different from those of the full rock (coal) anchor body. With the increase in the pull-out rate, the maximum pull-out load of the bolt on the coal&ndash;rock combined anchor body increases first, then decreases, and finally tends to be stable. Under the condition of a low drawing rate, the bearing capacity of the coal&ndash;rock combined anchor system can be greatly improved, but when the pull-out rate exceeds 20 mm/min, the bearing capacity of the anchor system is reduced. The debonding process of the anchoring section of the coal&ndash;rock combined anchor body gradually expands from the beginning section of the anchor to the bottom of the borehole. The coal&ndash;rock combined anchor body undergoes time differential development of cracks, and the failure of the coal and rock mass occurs at different times. Its failure process can be divided into three stages: (1) the coal anchor and rock anchor act together; (2) the rock anchor acts alone; and (3) the coal anchor and rock anchor have residual action

Physical Similarity Simulation of Deformation and Failure Characteristics of Coal-Rock Rise under the Influence of Repeated Mining in Close Distance Coal Seams

Aiming at the problem that it is difficult to achieve accurate laying of model and precise excavation of roadways in special surrounding rock structure roadway according to conventional physical similarity simulation, which reduces the reliability of experimental results. An accurate laying of model and precise excavation of roadway method, named “labeling positioning and drawing line, presetting roadway model” (LPDLPRM), was proposed. The physical similarity simulation of deformation and failure characteristics of surrounding rock of coal-rock rise, under the influence of repeated mining in close distance coal seams, was carried out based on the method and infrared detection. The results show that the coal-rock rise in close distance coal seams was affected by repeated mining disturbances, and the surrounding rock of coal-rock rise was characterized by obvious asymmetric deformation, specific for the stress and strain near the coal pillar were higher than that of other parts, and cracks near the coal pillar were denser than other parts; when the coal seam is mined in which the coal-rock rise is located, the stress concentration of the surrounding rock near the rise was weakened by mining pressure relief in the upper coal seam; the stress concentration of the surrounding rock near the rise increases when the coal and the lower coal seam are mined, and the stress on the right side (coal pillar side) near the coal-rock rise was the most concentrated. Therefore, it is important to take measures to strengthen support near the coal pillar and to control asymmetric deformation when the coal-rock rise is influenced by repeated mining

Crystal structures and biological evaluation of Cu(II) complexes with 3-ethyl-2-acetylpyrazine N(4)-isopropylthiosemicarbazone

1305-1313Five Cu(II) complexes, [Cu(L)2]&middot;CH3OH (1), [CuLCl] (2), [CuLBr] (3), [CuL(NO3)] (4) and [Cu2(L)2(SO4)]&middot;3H2O&middot;CH3OH (5), based on HL (where HL = 3-ethyl-2-acetylpyrazine N(4)-isopropylthiosemicarbazone) have been synthesized and characterized by X-ray diffraction analyses. The complexes (1) and (2) are mononuclear, while the other three are binuclear. In vitro experiments carried out to investigate the effect of complexes (1-5) on human hepatoma cells SMMC-7721, human gastric cancer SGC-7901 and human pancreatic cancer Patu-8988 show that complexes (1-5) can inhibit the proliferation of all the three cancer cell lines. The inhibition of cell growth is related to increase of tumor cell apoptosis, which is further confirmed by results of western blotting wherein the expression of p53 and Bax increased, and expression of Bcl-2 decreased in complex (3) treated SMMC-7721 cells