The Self-sustained Catalytic Combustions And Reaction Mechanisms Of Carbon Monoxide Over Transition Metal Oxide Catalysts

Off-gases produced in basic oxygen furnace（BOF）process contain substantial high-concentrate CO,which is typically treated by CH₄ combustion method.This method does not only waste much energy but also cause more CO₂ and NO_x emissions.CO self-sustained combustion is recognized to be a safe and flameless technology with high efficiency and low cost.And the inexpensive and effective transition metal oxides possess considerable potentiality for CO self-sustained combustion,which are often used as the alternatives of noble metal catalysts.Focusing on copper oxides and cobalt oxides,this research expands the discussions about the performances and reaction mechanisms of the catalysts.The results are as follows:（1）Morphological inverse Ce O₂/Cu₂O catalysts were synthesized by solution phase synthesis-impregnation method.And the morphological effects among different Cu₂O planes and facet interactions between Cu-Ce on the catalytic activity were explored.From the results,under the dual effects,Ce O₂/Cu₂O-8（1 1 1）shows the most exceptional catalytic activity,with T₉₀ of 185℃,which is 30℃lower than that of Cu₂O-8.This can be mainly attributed to the coordinately unsaturated Cu⁺and the strongest facet interaction on（1 1 1）plane.Simultaneously,associated with XRD,XPS,H₂-TPR and O₂/CO-TPD results,the excellent activity of Ce O₂/Cu₂O-8（1 1 1）lies in the highest content of Cu⁺,Ce³⁺and oxygen vacancies as well as the best reducibility and CO/O₂ adsorption capacity.Furthermore,facet interaction can effectively decrease the crystallinity of the catalysts,contributing to the lattice distorts,oxygen vacancies and eventually the facilitated activities.The reaction mechanism is found to follow Mars-van Krevelen（M-K）mechanism over the catalysts by in-situ DRIFT and kinetic experiment,where CO adsorbs on Cu⁺and reacts with adjoint lattice oxygen to form CO₂.（2）Modified La_0.9M_0.1Co O₃（M=Ce,Sr）perovskite catalysts were prepared via sol-gel method,over which the effects of facilely adding glucose and Ce/Sr doping on the catalytic activities were investigated.The results indicate that catalytic activity can be improved in both ways.Glucose plays a distinctive role in forming more oxygen vacancies and Co³⁺since it can create a reducing atmosphere and take away the oxygen atoms from the catalysts.Moreover,the doping of Ce/Sr can also cause lattice defects and oxygen vacancies.CO self-sustained combustion is successfully achieved on LCCO-G.Combined with XPS,H₂-TPR and O₂/CO-TPD results,the marvelous performance of LCCO-G mainly determines on the promoted concentrations of Co³⁺,Ce³⁺and oxygen vacancies.Proven by in-situ DRIFT and kinetic experiment,Langmuir-Hinshelwood（L-H）mechanism properly illustrates the reaction pathway over the perovskite catalysts,where monodentate carbonates are the critical intermediates.Besides,LCCO-G is capable of sustaining 100%conversion at 760℃for a long period with good durability.