Self-sustained catalytic combustion of CO enhanced by micro fluidized bed: stability operation, fluidization state and CFD simulation

A micro fluidized bed reactor was used to study the self-sustaining catalytic combustion of carbon monoxide(CO).The Cu_(1−x)Ce_(x)O_(y) catalyst,as well as the pure CuO and CeO_(2),are used to investigate the contributing mechanism of different active sites including dispersed CuO and Cu–Ce solid solutions.The ignition temperature(Ti)of CO over these catalysts at a flow rate of 2000 mL/min followed the order:74℃(Cu_(0.5)Ce_(0.5)O_(y))<75℃(Cu_(0.25)Ce_(0.75)O_(y))<84℃(Cu_(0.75)Ce_(0.25)O_(y))<105℃(CuO)<500℃(CeO_(2)).Furthermore,the lean combustion limits(equivalence ratioϕ)over these catalysts under the flow rates of 750–3000 mL/min(through fixed,bubbling,and fluidized bed)were also measured,which are Cu_(0.5)Ce_(0.5)O_(y)<Cu_(0.25)Ce_(0.75)Oy<Cu_(0.75)Ce_(0.25)O_(y)<CuO<CeO_(2).The fluidized bed was simulated using the Eulerian two-fluid model(TFM)coupled with a diffusion/kinetic-limited reaction model to evaluate the influence of operation conditions on the self-sustained combustion of CO.The predicted maximum temperature agreed with the experimental measurements,demonstrating the validity of the kinetic model and simulation parameters.The results of catalytic combustion with increasing CO concentrations suggest that the catalytic combustion reaction could co-exist with the flamed combustion.When a high concentration of CO is used,a blue-purple flame caused by CO combustion appears in the upper part of the fluidized bed,indicating that the range of CO-containing exhaust gas purification could be expanded to a larger range using the fluidized-bed catalytic combustion technique.

Role of oxygen species and active phase of CuCeZrO_(x) prepared with bacterial cellulose for toluene catalytic oxidation

The present study investigates the active phases and the role of oxygen species in the toluene oxidation process over CuCeZrO_(x) catalysts prepared with bacterial cellulose(BC),and compares them with nitric acid pickling CuCeZrO_(x)-BC(H)and CeZrO_(x)-BC catalysts.The investigation is carried out using in-situ DRIFT,O_(2)-TPD,H_(2)-TPR,XRD,and TEM techniques.Our findings suggest that dispersed CuO species on the catalyst surface,Cu-Ce-Zr-O,and Ce-Zr-O solid solutions are active for toluene oxidation over CuCeZrO_(x)-BC,with corresponding activities decreasing successively.The in-situ DRIFT results demonstrate that gaseous oxygen facilitates the chemisorption of toluene on active oxygen species,forming benzoyl oxide species and partially oxidizing the absorbed intermediates to benzyl alcohol at room temperature.Furthermore,lattice oxygen is experimentally found to be involved in the deep oxidation of toluene,and the lattice oxygen present in dispersed CuO species dominates the toluene oxidation process over CuCeZrO_(x)-BC.

Comparative study of MCe_(0.75)Zr_(0.25)O_(y)(M=Cu,Mn,Fe)catalysts for selective reduction of NO by CO:Activity and reaction pathways

Basic oxygen furnace steelmaking leads to the production of CO-rich off-gas.When CO and NO are combined in off-gas,selective catalytic reduction by CO(CO-SCR)effectively achieves the synergistic removal of both pollutants.In this paper,CuCe_(0.75)Zr_(0.25)O_(y),MnCe_(0.75)Zr_(0.25)O_(y),and FeCe_(0.75)Zr_(0.25)O_(y) catalysts are prepared and evaluated for their CO-SCR activity,and the results show that the reaction system needs to be anaerobic;thus,the CO-SCR reaction can be dominant.The T_(90) values of CuCe_(0.75)Zr_(0.25)O_(y) and FeCe_(0.75)Zr_(0.25)O_(y) are 200℃ and 223℃,respectively.The activities of these two catalysts are higher than that of MnCe_(0.75)Zr_(0.25)O_(y)(T_(90)=375℃).Linear nitrate and bridged bidentate nitrate are the main intermediate species involved in NO conversion on the catalyst surface,and bidentate CO_(3)^(2-)􀀀coordination is the main intermediate species involved in CO conversion on the catalyst surface.CuCe_(0.75)Zr_(0.25)O_(y) has high lattice oxygen mobility and is more likely to react with NO and CO.In the presence of oxygen,most CO is oxidized by O_(2),which increases continuously to 100%,100%,and 98%for CuCe_(0.75)Zr_(0.25)O_(y),FeCe_(0.75)Zr_(0.25)O_(y),and MnCe_(0.75)Zr_(0.25)O_(y),respectively;additionally,CO is oxidized by O_(2),and the CO-SCR reaction cannot be carried out.

Insights on copper,manganese,and Nickel/ZSM-5 catalytic mechanisms for nitric oxides selective reduction with ammonia

The elucidation of the selective catalytic reduction mechanisms over state-of-the-art metal-promoted zeolites is essential for nitric oxides removal in automobile and stationary source applications.In this work,H/ZSM-5 catalysts modified with transition metals,including copper,manganese,and nickel,were prepared by using an incipient wetness impregnation method and were evaluated for the selective reduction of nitric oxides with ammonia.Results indicate that copper/ZSM-5 exhibits the highest catalytic activity,with>90%nitric oxide conversion at a broad operation temperature window(221–445◦C).The nitric oxide conversion profiles of nickel/ZSM-5 shows two peaks that correspond to weak activity among the catalysts;the low-temperature peak(290◦C)was induced by nickel clusters dispersed on the ZSM-5 surface,while the high-temperature peak(460◦C)was assigned to the bulk nickel oxides.The size of granular nickel monoxide crystallites with an exposed(202)plane is 2–30 nm,as confirmed by Scanning electron microscopy,X-ray diffraction,and Transmission electron microscope measurements.Temperature-programmed reductions with hydrogen results testified that the copper and nickel cations,as the main species contributing to selective catalytic reduction,were reduced via Cu^(2+)/Cu^(+)→Cu^(0) and Ni^(2+)→Ni^(0) for copper/ZSM-5 and nickel/ZSM-5,respectively,while for the manganese/ZSM5,the Mn3+species in manganese clusters were reduced to Mn^(2+) by hydrogen.Particularly,temperatureprogrammed desorption coupled with mass spectrometer(TPD-MS)and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)were comprehensively used to reveal the relationship between zeolite structure and catalysts’properties for improving selective catalytic reduction.These results confirm that the ammonia is adsorbed and activated on both Brønsted and Lewis acid sites.The nitrous oxide desorbs in two stages during nitric oxide-TPD-MS measurements,corresponding to the desorption of nitric oxide bounded to amorphous clusters and the nitric oxide strongly bounded to bulk metal oxides,respectively.The selective catalytic reduction process follows the L-H mechanism at low temperatures,in which nitric oxide and ammonia molecules were adsorbed and activated on the catalyst surface.The selective catalytic reduction rates reached the maximum value of 1.8×10^(8)(218◦C),6.4×10^(7)(227◦C),and 3.9×10^(7)s^(−1)(235◦C)for copper,manganese,and nickel/ZSM-5,respectively.