Cerium doped copper/ZSM-5 catalysts used for the selective catalytic reduction of nitrogen oxide with ammonia

The CuCe/ZSM-5 catalysts with different cerium loadings (0, 0.5, 1.0, 1.5 and 2.0wt.%) was investigated to evaluate the correlation between structural characteristics and catalytic performance for the selective catalytic reduction (SCR) of NO by NH3. It was found that the addition of cerium increased copper dispersion and prevented its crystallization. According to the results of X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction by hydrogen (H2-TPR), copper species were enriched on the ZSM-5 grain surfaces and part of copper ions was incorporated into the cerium lattice. Addition of cerium improved the redox properties of the CuCe/ZSM-5 catalysts, owing to the higher valence of copper and mobility of lattice oxygen than those of Cu/ZSM-5 catalyst. Hence the introduction of cerium in Cu/ZSM-5 improved significantly NO conversion. On the one hand, the cerium introduction into Cu-Z enhances their low-temperature activities. 95% NO conversion is reached around 197°C for Cu-Z while the corresponding temperature value decreases to 148°C for CuCe4-Z. On the other hand, the temperature range of efficient NO reduction (95%) also extends to higher temperature when the cerium are added to Cu/ZSM-5. Among the Cu-Ce/ZSM-5 catalysts tested, the CuCe4-Z sample exhibits the highest catalytic activity with the temperature range for 90% NO removal of 148-427°C

A facilitated synthesis of hierarchically porous Cu-Ce-Zr catalyst using bacterial cellulose for VOCs oxidation

Highly active CuO-CeO2-ZrO2 catalysts were prepared by sol-gel method, using environmentally friendly bacterial cellulose (BC) as structure directing regent. The catalyst designed with commercial BC (Com-BC) exhibited catalytic performances in toluene (T100 =220 oC) and ethyl acetate oxidation (T100 =170 oC) superior to the catalysts prepared by traditional methods. Furthermore, excellent stability was obtained and no deactivation was observed during the 100 h on stream in toluene and ethyl acetate oxidation at T100. The excellent activity and stability of Com-BC can be explained by the hierarchically porous structure, abundant oxygen vacancies, and good reducibility

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

Self-sustained CO Combustion Induced by CuCe0.75Zr0.25Oy Catalysts with Different Pore-forming Methods

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% O-2/N-2), the T-10 (70 degrees C), T-50 (73 degrees C) and T-90 (78 degrees C) of the cellulose catalyst are obviously lower than those of the other catalysts, where T-10, T-50 and T-90 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

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

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 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

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