The paper deals with the effect of modification with cobalt of a series of LaFe1-xCoxO3 mixed-oxide perovskites as catalyst precursors in the combined reforming of methane with CO2 and O-2 for the production of syngas. The perovskite type oxides were synthesized by fine chemical using the citrate sol-gel method and characterized by techniques such as FT-IR, BET surface area, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), TPR and inductively coupled plasma emission spectroscopy (ICP), under the condition of as-synthesized, reduced and used samples. The results showed that through this synthesis it is possible to obtain highly crystalline, homogeneous and pure solids, with well-defined structures. After reduction, the stabilization by the presence of iron of highly dispersed Co metallic particles from the cation on position B over the corresponding oxides was evidenced, decreasing deactivation by avoiding the sintering of metals and coke formation on the surface of the catalysts.The existence of strong Fe-Co interaction in the LaFe1-xCoxO3 with x = 0.4-0.6 produces a synergetic effect improving methane conversion and H-2 production. (c) 2005 Elsevier B.V. All rights reserved.

El metodo de auto-combustion fue utilizado para sintetizar una serie de oxidos tipo perovskita La1-xAxNiO3, donde el cation La3+ es sustituido parcialmente por Sr2+ y Mg2+. Los analisis de difraccion de rayos X indican que el Sr ejerce un efecto notable sobre la estructura de los solidos sintetizados, obteniendose una fase simple de oxido tipo perovskita para un grado de sustitucion x£0,1 y una mezcla de fases de oxidos tipo espinelas y NiO para x³0,2. Se observa que el estado de oxidacion formal del Ni disminuye desde 3+ (x= 0) hasta 2,6+ (x= 0,4), indicando que el Sr facilita la reduccion ya que promueve la capacidad de aceptacion de electrones sobre la muestra. El Mg, por otra parte, no produce un solido con estructura perovskita. Los estudios de reduccion a temperatura programada (RTP) revelan que estos procesos ocurren a traves de especies intermediarias hasta formar NiO, SrO y La2O3, fases que se relacionaran con la actividad presentada durante los estudios cataliticos sobre estos solidos precursores

The auto-combustion method was used to synthesize a series of La(1-x)A(x)NiO(3) perovskite type oxides where the La3+ cation is partially substituted by St(2+)and Mg2+. The X-ray diffraction analysis indicates that Sr has a strong effect on the structure of the synthesized solids producing a single perovskite type structure x < 0.1, while a mixture ofspinella t ' ype oxides and NiO phases were observed for x > 0.2. It is observed that the formal oxidation state of Ni decreases from 3+ (x= 0) to 2.6+ (x= 0.4), indicating that Sr enhances the reduction of the cations by promoting the electron acceptance capacity of the perovskite. No perovskite type structure was obtained with Mg. The temperature program reduction studies (TPR) showed that the reduction proceeds through a step wise process to form Ni-0, SrO and La2O3 phases which could be related to the activity presented in later catalyltic studies of these precursor solids.

Perovskites type oxides La1−xCaxRu1−xNixO3 were synthesized by the citrate sol–gel method. Characterization was carried out underlying the modification of metal catalysts by promoters by total or partial substitution of A- and B-site cations. The influence of Ru partial substitution by Ni in the LaRuO3 structure and of La by Ca on LaRu0.8Ni0.2O3 was also investigated in the dry and combine reforming of methane. All perovskites series, showed a well-defined perovskite structure with surface areas between 2 and 17 m2/g. After reduction Ru(Ni) crystallites size in the order of 10–15 nm were produced. An oxygen deficiency was shown by most perovskites. Substitution of La by Ca of smaller ionic radium decreases the stability of the perovskites and lowers their reduction temperature. Among the calcium series, La0.8Ca0.2Ru0.8Ni0.2O3, proved to be the most active precursor catalyst with the highest selectivity to syngas. Correlation between the effect of partial or total substitution of La by Ca as A-site cation of the precursor perovskite, the catalytic activity and stability of in situ formed Ru(Ni) particles was established.

Five perovskite oxides with the composition La1-x KxMnyFe1-yO3 (0 less than or equal to x, y less than or equal to 0.2) were synthesized by the co-precipitation method. Techniques such as chemical and XR fluorescence analysis, powder X-ray diffraction (XRD), BET surface area, IR, EPR and Mossbauer spectroscopy were applied to characterize the structural features of the perovskites. The activity of the solids was strongly dependent on the presence of iron carbides. It was observed that K promotes the reducibility of the solid to alpha-Fe giving rise to more carbide phases. Mn produces a significant increase in alkenes production. The combined presence of both K and Mn (La0.9K0.1Fe0.9Mn0.1O2.9) strongly modified the selectivity of the oxides, giving rise to a stable catalyst with high yield of C-2-C-4 alkenes. (C) 2002 Elsevier Science B.V. All rights reserved.

The present work intends to illustrate the effects of precursor and support composition on the structure and performance of Pd-based catalysts for the synthesis of methanol and higher oxygenated compounds. The power of the XRD technique and the reaction itself, as characterisation tools, was evidenced. The hydrogenation of carbon monoxide has been studied over palladium supported on ZnO, Zr(OH)4 and ZrO2 using PdCl2 and Pd(NO3)2 as salt precursors. Catalysts were characterised by XRD and Raman spectroscopy. The results show that activity and selectivity are strongly dependent on the salt precursor and on the acid–basic properties of the support. As seen from the CH3OH/DME ratio, the order of acidity of the supports is: Zr(OH)4>ZrO2>ZnO independently of the salt precursor used. The Pd(NO3)2/ZnO catalyst shown the highest methanol selectivity which was related to the presence of large particles of a PdZn alloy. A double bifunctionality on the catalysts for the production of higher oxygenated seems evident. On the one hand, an acid–base bifunctionality of the support seems to be needed for the formation, stabilisation, chain growth and further reactivity of intermediates such as formate, as well as for the dissociative adsorption of CO, and on the other hand, a metal-support bifunctionality, where the palladium metal particles would play the role of hydrogenating the intermediates and possibly adsorb non-dissociatively the CO.

A series of perovskite-like oxide in which the A-site cation of the precursor perovskite, LaRu0.8M0.2O3, was partially or totally substituted by calcium, samarium and neodymium have been used to produce in situ nanoparticles of Ru(Ni) well dispersed on a stable support for the carbon dioxide reforming of methane. Perovskites of the type Ln(x)Ca(1 - x)Ru(0.8)Ni(0.2)O(3) (Ln = La3+, Sm3+, Nd3+) were synthesized as catalysts precursors. The reduced solids of nominal composition (Ru,Ni)/CaO and/or La2O3, Sm2O3, Nd2O3, were used as catalysts. The La1 - xCaxRu0.8Ni0.2O3 series showed a well-defined perovskite structure with surface areas between 3 and 10 m(2)/g. However, when lanthanum was replaced by samarium and neodymium, the presence of pyrochlore structures, together with the perovskites, were obtained. After reduction Ru(Ni) crystallites size between 9 and 17 nm were produced. The substitution of La by cations of smaller ionic radii (Ca, Nd, Sm) decrease the stability of the perovskites and lower their reduction temperature. Among the calcium series, La0.8Ca0.2Ru0.8Ni0.2O3 and La0.5Ca0.5Ru0.8Ni0.2O3, proved to be the most active catalysts with the highest selectivity to CO. While samarium-containing perovskite was the best among the lanthanide series. Correlations between the effect of partial or total substitution of A-site cations of the precursor perovskite and the catalytic activity and stability of in situ formed nickel and ruthenium particles were established. (C) 2003 Published by Elsevier B.V.

Iron-based catalysts have favorable activity and selectivity properties for the CO and CO2 hydrogenation reactions. Several Fe phases (oxides and carbides) can be present in these catalysts. The interaction of Fe with the other components of the catalyst (support, promoters) can affect the ease of reduction and also its transformation during the reactions. In this work, the relationship between catalytic behavior in the CO and CO2 hydrogenation reactions and the Fe phase composition of fresh and reacted catalysts was studied. Two types of catalysts were tested: a laterite and the other one made of iron supported on alumina, both unpromoted and promoted with K and Mn. Only those Fe species which can be reduced-carburized, by means of a pretreatment or by an in situ transformation under the reaction, seem to be able to perform the CO or CO2 hydrogenation. The reoxidation of the Fe carbide to magnetite was not associated to deactivation. The selectivity seems to be more affected by Fe species difficult to reduce than by magnetite produced by reoxidation.

Perovskites type oxides LaMO3 (M = Ru, Ni, Mn) were synthesized by the citrate Sol-Gel method and tested as catalysts for the CO2 reforming of methane. The influence of Ru partial substitution for Ni in the LaRuO3 structure on the activity and selectivity performance was also investigated. The results were compared with those obtained with catalyst samples prepared by wet impregnation. The effects of parameters such as reaction temperature, space velocity, CH4/CO2 ratio and time on stream were investigated and optimized to higher yields of syngas. XRD, BET surface area, TEM-EDX, IR, XPS, TPR and H2 chemisorptions characterized all the solids. Among all the solids investigated, the LaRu0.8Ni0.2O3 precursor was the most active and selective catalyst, reaching values of 89% and 90% in methane conversion and CO selectivity respectively even after 150 hours on stream. A significant decrease in coke deposition for all the catalysts was obtained which constitutes an advantage for future developments of commercial reforming catalysts.

In this work a series of Ni and Ru supported on LnMnO3 perovskite-like oxide has been studied as catalyst precursors for the carbon dioxide reforming of methane to syngas. The LaMnO3 perovskite was synthesized by the citrate sol-gel method. The effect of parameters such as reaction temperature, amount of supported metal, space velocity, reactant partial pressure, and time on stream were investigated, and optimized to higher yields of syngas. Different techniques were applied to characterize the structural features of the LaMnO3 perovskite support and of the catalysts. It was observed that the citrate method produced a homogenous solid with a cubic crystal structure. The catalytic activity, the CO yields and selectivity for the best Ni (10%) and Ru (1%) catalysts was similar when compared under isoconversion conditions. CH4 and CO2 conversions were approximately 39% and 54% respectively, while the CO selectivity reached a value of 78%. No reactivity was observed for the pure perovskite. A significant decrease in coke deposition for Ni catalysts was obtained which constitutes an advantage for future developments of commercial reforming catalysts.

Physicochemical and catalytic properties of titania-supported 12-molybdophosphates have been investigated. The samples were characterized by the S(BET) method, Fourier-transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies, temperature-programmed desorption (TPD) of ammonia and temperature-programmed reduction (TPR). The effect of temperature pretreatment on the catalytic behaviour of the samples in methanol oxidation was investigated. A significant change of selectivity to the main reaction products: dimethyl ether (DME) and formaldehyde (HCHO), as a function of the acid properties of the catalysts was observed. The highest selectivity to DME at 523 K suggested that the undecomposed molybdophosphoric acid (HPMo) on titania behaves as an acid catalyst. Pretreatment of the samples at higher temperatures (up to 723 K) and replacement of the protons in HPMo by cations (Co and Ni) lead to development of the redox properties (HCHO formation) of the catalyst, due to the suppression of the Brönsted acidity. The IR and XPS results provided clear evidence for the preservation of Keggin unit up to 623 K pretreatment after test reaction.

The behavior of unpromoted and K-promoted Fe/Al2O3 catalysts in both, CO2 and CO hydrogenation reactions at 553–563 K and 1.2 MPa was compared. To attain different degrees of interaction between Fe and the support, three different procedures were followed to prepare the catalysts: impregnation, precipitation and physical mixing of the support with Fe oxide obtained from citrate decomposition. Fe-phase composition of pretreated (reduction-carburization) and after reactions catalysts was analyzed by Mössbauer spectroscopy. Correlation between Fe phase composition of pretreated catalysts and product selectivity was evident. A lower proportion of carbided Fe in fresh catalysts led to higher methane selectivity and higher alkanes/alkenes and internal/terminal alkenes ratios for both reactions, CO2 and CO hydrogenation. This relationship was observed independently of the reoxidation of carbide to magnetite, which took place during reactions for most catalysts. Lighter hydrocarbons were produced from CO2 hydrogenation compared to CO hydrogenation. Higher selectivities to C2–C4 alkenes were obtained from the first reaction through promotion with K.

Hydrogen production by partial oxidation of methanol (CH3OH+1/2 O2 ⇄2 H2+CO2) was studied over ZnO- and ZrO2-supported Pd catalysts. Catalyst performance was investigated under feed ratios O2/CH3OH (molar) of 0.3 and 0.5 at 503–543K. Irrespective of the large difference in BET area of Pd/ZnO and Pd/ZrO2 catalysts, significant differences were observed when comparing H2 selectivities. For the 1% Pd/ZnO catalyst, reaction occurs through consecutive oxidation → reforming steps. However, the behavior of catalyst 1% Pd/ZrO2 approached that expected for Group 8 metals, that is, although the oxidation products are observed as for the catalyst 1% Pd/ZnO, the decomposition reaction seems to occur to a greater extent. Catalyst characterization by TPR, X-ray diffraction and XPS revealed that PdZn alloys can be formed upon reduction of Pd/ZnO catalysts at moderate temperatures.

Ruthenium catalysts supported on ZrO2/Al2O3 oxides were prepared. They were subsequently modified with promoters such as It and Mo. The catalysts were prepared by incipient wetness impregnation and characterised by means of surface area (B.E.T.), chemical analysis (ICP), hydrogen chemisorption and CO hydrogenation reaction. The results obtained shown that the catalytic behaviour of the ruthenium can be modified satisfactorily. It was possible to obtain an appreciable selectivity toward the fraction of oxygenated compounds with the catalysts composed of 1.5% Ru 1/4 monolayer of ZrO2/Al2O3, promoted either with potassium or molybdenum. When alumina was used as support, ruthenium was lost in the form of volatile carbonyls (formation favoured at low temperatures and high pressures), due to the weak interaction between the ruthenium and the alumina. When using a mixture of ZrO2 and Al2O3 as support, a catalyst was obtained where the interaction between the ruthenium and the support was stronger avoiding this problem.

The behaviour in syngas conversion of Me/AlPO4-5 and MeAPO-5 (Me=Fe, Co, ∼4wt%), as well as that of hybrid systems comprising an iron Fischer–Tropsch (FT) catalyst physically mixed with SAPO-5, FAPO-5, SAPO-11 and FAPO-11, was studied at 1.2MPa, 573K and H2/CO=1. Conversion of CO was much lower for Fe/AlPO4-5 and MeAPOs than for Co/AlPO4-5, which could be related to the presence of the metal in high-oxidation states on the former. Significant differences in selectivity were observed as a result of changes in the type of metal and in the way that the metal is introduced in the catalyst (added to the synthesis gel or impregnated on the molecular sieve). These differences in selectivity were explained in terms of the facility of forming alkenes (related to metal sites) and the presence of acid sites. Alkenes formed on the FT catalyst underwent oligomerisation, cracking, skeletal isomerisation and hydrogen transfer reactions in the presence of the physically mixed SAPO-5 and FAPO-5. Double bond shift and skeletal isomerisation were the only alkene transformations observed on the mixtures of FT with AEL-like catalysts (FT-FAPO-11 and FT-SAPO-11). Deactivation of acid sites with time-on-stream was evidenced for the physical FT-molecular sieves mixtures. However, their higher selectivity toward light hydrocarbons, as compared to that in the absence of molecular sieves, persisted. It was observed that the FAPO phase (FAPO-5 or FAPO-11) added to the FT catalyst led to an increase in the syngas conversion, probably due to the participation of iron-species associated with the molecular sieves.