Perovskite-Like Mixed Oxides (LaSrMn1-x Ni (x) O4+delta, 0 a parts per thousand currency sign x a parts per thousand currency sign 1) as Catalyst for Catalytic NO Decomposition: TPD and TPR Studies

Catalytic NO decomposition on LaSrMn1-x Ni (x) O4+delta (0 a parts per thousand currency sign x a parts per thousand currency sign 1) is investigated. The activity of NO decomposition increases dramatically after the substitution of Ni for Mn, but decreases when Mn is completely replaced by Ni (x = 1.0). The optimum value is at x = 0.8. These indicate that the catalytic performance of the samples is contributed by the synergistic effect of Mn and Ni. O-2-TPD and H-2-TPR experiments are carried out to explain the change of activity. The former indicates that only when oxygen vacancy is created, could the catalyst show enhanced activity for NO decomposition; the latter suggests that the best activity is obtained from catalyst with the most matched redox potentials (in this work, the biggest Delta T and Delta E values).

Co-Cu-Al mixed oxides derived from hydrotalcite-like compound for NO reduction by CO

Various hydrotalcite based catalysts were prepared for catalytic removal of NO (NO reduction by CO). The general formula of hydrotalcite compounds (HTLc) was Co-Cu-Al-HTLc. Precalcination of these materials at 450 degrees C for NO reduction by CO, was necessary for catalytic activity. All catalysts except Co-A1 and Cu-Al have very good activity at lower temperature for NO reduction by CO. All samples were characterized by XRD and BET. The tentative reaction mechanism was also proposed.

Catalytic reduction of NO, by CO on hydrotalcites-derived mixed oxides CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu)

Two series of mixed oxides, CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu), were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc). The ratio of Mg: Al: M (or Co: Al: hi) was 3:1:1. The catalytic activity of all samples for the reaction of NO + CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H-2-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced. The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, different ratio of Co:Al: Cu and at different calcination temperatures, were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO were investigated respectively for supporting the mechanism.

Preparation, charactreization, and catalytic properties of Co-M-Al (M = transition metal) mixed oxides derived from hydrotalcite-like compound

Hydrotalcite-like compounds (HTLcs) CoMAlCO3, where M stands for Cr, Mn, Ni, Cu, or Fe, were synthesized by coprecipitation. After calcination at 450 degrees C, they became mixed oxides with spinel-like structure. The mixed oxides were characterized by XRD, BET, chemical analysis and the adsorption of NO. The catalytic decomposition of NO and its reduction by CO were studied over these mixed oxides. The study showed that the catalytic activity for removal of NO, was very high. The reaction mechanism is proposed and the effects of d-electrons of the transition metals on catalytic activity are elucidated.

Catalytic reduction of NO by CO with hydrotalcite derived mixed oxides

Catalysts with spinel structure derived from Hydrotalcite-like Compounds (HTLcs) containing cobalt have been investigated in NO catalytic reduction by Co. It was found that catalysts with spinel structures derived from HTLcs had obviously higher activity than that prepared from general methods. A two-step reaction was observed during the reaction curse: NO was first reduced to N2O by Co, and with the increase of temperature, the N2O was reduced to N-2. The reactivity of the catalysts studied increased with the amount of cobalt-content in the catalyst, and decreased with the calcination temperature. The crystal defect would play an important role in the reaction.

Synthesis, characterization and catalytic behavior of layered mixed oxides La4BaCu5-xMnxO12 in NO reduction by CO

A series of sample having the stoichiometry La4BaCu5-xMnxO12 (x = 0 similar to 5) were prepared, characterized by XRD, IR and H-2 - TPR and used as catalyst for NO + CO reaction. It was found that they have 5 - layered ABO(3) - type structure. The results of H-2 - TPR showed that the Cu ion was more easily reduced while a part of them was replaced by Mn ions. Their catalytic behavior to NO + CO reaction was investigate, La4BaCu2Mn3O12 showed the highest catalyst activity for the reaction than the others. The reaction mechanism is discussed:the activity of the catalysts could be attributed to the Cu ions, but it was improved when Mn ions took the place of some Cu ions.

Layered La-Ba-Cu mixed oxides with perovskite structure as catalyst for NO reduction by CO

The mixed oxides, including LaBa2Cu3O7, LaBaCu2O5, La4BaCu5O12 with perovskite structure, were prepared. The catalysts were characterized by means of chemical analysis, XRD, H-2-TPR. It was found that their structures were layered ABO(3) perovskite structure and they were the active catalysts for the NO reduction by CO. The existence of Cu3+ is an important factor to give the catalysts a high activity for the NO reduction by CO.

Physico-chemical properties and catalytic behavior of LnSrNiO(4) mixed oxides for NO decomposition

A series of LnSrNiO(4)(A(2)BO(4), Ln = La, Pr, Nd, Sm, Gd) mixed oxides with K2NiF4 structure, in which A-site(Sr) was partly substituted by individual light rare earth element, was prepared. The solid state physico-chemical properties including crystal structure, defect structure, IR spectrum, valence state of H-site ion, nonstoichiometric oxygen, oxygenous species, the properties of oxidation and reduction etc. as well as the catalytic behavior for NO decomposition on these mixed oxides were investigated. The results show that all of these mixed oxide catalysts have high activity for the direct decomposition of NO(at 900 degrees C the conversion of NO is more than 90%). The effect of the substitution of light rare earth elements at A-site on catalytic behavior for NO decomposition was elucidated.

Perovskite-like mixed oxides La2-x(Sr,Th)(x)CuO4+/-lambda

Two groups of mixed oxides La2-xThxCuO4+/-lambda (0.0 less than or equal to x less than or equal to 0.4) and La2-xSrxCuO4+/-lambda (0.0 less than or equal to x less than or equal to 1.0) were prepared. Their crystal structures were studied with XRD and IR spectra, etc. Meanwhile, the average valence of Cu ions and nonstoichiometric oxygen (lambda) was measured through chemical analyses. Catalysis of the abovementioned mixed oxides was investigated in phenol hydroxylation, good results were obtained for some mixed oxides, and found that the catalysis of these mixed oxides have close relation with their defect structure and composition. A radical substitution mechanism was also proposed for this catalytic reaction.

Catalysis of the rare earth containing mixed oxides Ln(2)CuO(4) in phenol hydroxylation

Mixed oxides Ln(2)CuO(4+/-lambda)(Ln = La, Pr, Nd, Sm, Gd) with K2NiF4 structure were prepared. Their crystal structures were studied with XRD and IR spectra. Meanwhile, the average valence of Cu ions and nonstoichiometric oxygen (lambda) were determined through chemical analyses. Catalysis of the above-mentioned mixed oxides in the phenol hydroxylation was investigated. Results show that the catalysis of these mixed oxides has close relation with their structures and composition. Substitution of A site atom in Ln(2)CuO(4+/-lambda) has a great influence on their catalysis in the phenol hydroxylation.

Preparation, physico-chemical behavior and catalytic property for ammonia oxidation of perovskite like mixed oxides La2-xSrxCuO4-lambda

A series of Sr2+ doped perovskite like oxides La2-xSrxCuO4-lambda (x = 0 similar to 1) were prepared, the structure, lattice parameters, content of Cu3+, oxygen vacancies created by Sr2+ substitution and composition of these complex oxides were studied by XRD and iodic titration method. The redox ability,active oxygen species and surface image were evaluated and analyzed with TPD, TG, XPS and SEM measurements. The catalytic activity for ammonia oxidation over these oxides was tested, and the relationship among the catalytic properties, structure, nonstoichiometric oxygen,redox ability and surface behavior were correlated and some information on the mechanism of ammonia oxidation was obtained.

Y-Ba-Cu-O mixed oxides for production of diphenols in liquid-solid phase

Superconductor mixed oxides were often used as catalysts at higher temperature in gas phase oxidations, and considered not suitable for lower temperature reactions in the liquid-solid phase; here the catalysis of YBa2Cu3O7+/-x and Y2BaCuO5+/-x in the phenol hydroxylation at lower temperature with H2O2 as oxygen donor was studied, and found that the superconductor YBa2Cu3O7+/-x, has no catalytic activity for phenol hydroxylation, but Y2BaCuO5+/-x does, even has better catalytic activity and stability than most previously reported ones. With the studies of catalysis of other simple metal oxides and perovskite-like mixed oxides, a radical substitution mechanism is proposed and the experimental facts are explained clearly, and draw a conclusion that the perovskite-like mixed oxides with (AO)(ABO(3)) and (AO)2(ABO(3)) structure have better catalytic activity than the simple perovskite oxides with (ABO(3))(3) structure alone, and (AO) structure unit is the key for the mixed oxides to have the phenol hydroxylation activity. No pollution of this process is very important for its further industrial application.

Superconductor mixed oxides La2-xSrxCuO4+/-lambda for catalytic hydroxylation of phenol in the liquid-solid phase

Superconductor mixed oxides are often used as catalysts at high temperature in gas-solid phase oxidations and considered not suitable for lower temperature reactions in the liquid-solid phase; here the catalysis of La2-xSrxCuO4+/-lambda (x = 0, 0.1, 0.7, 1) mixed oxides in phenol hydroxylation at lower temperatures are studied, and we find that the value of x has a significant effect on catalytic activity: the lower its value, the higher the catalytic activity; a mechanism is proposed to explain the experimental phenomena.

Relationship between the structure and catalytic activity of La2-xSrxNiO4-lambda(0<=x<=1) mixed oxides for NH3 oxidation

A series of samples having the composition of La2-xSrxNiO4(0 less than or equal to x less than or equal to 1) were prepared and used as catalysts for NH3 oxidation. It was found that the La and oxygen vacancies exist in the La2-xSrxNiO4-lambda(0 less than or equal to x less than or equal to 1). The unit cell volume decreases with the increase of x. For bath c and a parameters there appeared a turning point at x = 0.5. Doping with a lower valence cation Sr2+ in the case of La2NiO4 resulted in an increase of Ni3+, consequently the formation of oxygen vacancies, the increase of reducing ability and the increase of catalytic activity. In the oxygen TPD of La2-xSrxNiO4(0 less than or equal to x less than or equal to 1) appeared three peaks, the alpha' peak at about 400K was attributed to the surplus oxygen desorption, the a peak at 700K which approaches to a maxium at x = 0.6 was attributed to the oxygen adsorbed at oxygen vacancies. The beta peak at about 1000K which depends closely on the x and favors the catalytic activity was attributed to the reduction of Ni3+. The catalytic activity of La-2-x SrxNiO4 mixed oxides in the NH3 oxidation in general could be attributed to the extent of the redox reaction: 2Ni(2+) + O-2 + V-0(..) reversible arrow 2Ni(3+) + 20(-) where V-0(..) representes the oxygen vacancies and O- the oxygen species adsorbed at the vacancies.