Production of Syngas by CO2 Reforming on MxLa1−xNi0.3Al0.7O3−d

5892

Ind. Eng. Chem. Res. 2008, 47, 5892–5898

Production of Syngas by CO2 Reforming on MxLa1-xNi0.3Al0.7O3-d (M ) Li, Na, K) Catalysts Alieh Khalesi, Hamid R. Arandiyan, and Matin Parvari* Chemical Engineering Department, Iran UniVersity of Science and Technology, Tehran, Iran

This paper deals with the effect of modification with alkali metals (Li, Na, K) in MxLa1-xNi0.3Al0.7O3-d (x ) 0, 0.2, 0.5, 0.8, and 1.0) mixed-oxide perovskites as catalysts for the dry reforming of methane to produce syngas. The perovskite-type oxides have been synthesized by a sol-gel method using propionic acid as solvent and have been characterized by techniques such as Fourier-transform infrared (FT-IR), Bruner Emmet Teller surface area (BET), spectroscopy, X-ray diffraction (XRD), temperature programmed reduction (TPR), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), and carbon analysis (CA). Characterization of the MxLa1-xNi0.3Al0.7O3-d samples has shown that by applying this synthetic method it is possible to obtain highly crystalline, homogeneous, and pure solids with well-defined structures. However, when lanthanum was replaced by potassium or lithium, the reduction temperature was increased and the reaction temperature had to be increased to obtain good activity. After establishment of the optimal catalytic and experimental conditions, the selected catalysts did not show significant deactivation even after 15 h on stream, maintaining their activity and selectivity in the production of synthesis gas. Among all catalysts, Li0.2La0.8Ni0.3Al0.7O2.8 showed less coke formation; Na0.5La0.5Ni0.3Al0.7O2.5 showed high yield; and K0.5La0.5Ni0.3Al0.7O2.5 produced an H2/CO ratio close to 1 over a wide temperature range. These catalysts showed the best activities in lithium-, sodium-, and potassium-promoted series, respectively. In reactivity tests, methane conversions in excess of 90% and selectivities for H2 up to 80% at 850 °C under 1 atm have been achieved. 1. Introduction Natural gas reforming by means of dry reforming has recently achieved great importance as a way of producing hydrogen through the generation of synthesis gas.1 Great attention is being paid to the conversion of CH4 and CO2, the cheapest carboncontaining materials, into more valuable compounds by catalytic reactions.2 This is commercialized as the “Calcor Process”3 and the “SPARG Process”4 and mixing of Ni and Al oxides as a catalyst for this process.5 The conversion of CH4 to synthesis gas is usually carried out by steam reforming, leading to the formation of synthesis gas with an H2/CO ratio higher than 3.6 Since the replacement of H2O by CO2 results in a lower H2/CO ratio of 1:1 in the product gas, the combination of these two reforming reactions widens the utility of the synthesis gas, allowing its use, for example, in methanol synthesis or in the Fischer-Tropsch synthesis, which requires an H2/CO ratio of 2:1. This process has also received attention from the viewpoint of environmental protection because the emission of CH4 and CO2 into the atmosphere brings about global warming through the greenhouse effect, and these harmful gases can be simultaneously converted into useful synthesis gas.2 Ni has been reported to be an active catalyst for this reaction;7,8 however, the reaction is frequently accompanied by coke formation, especially on Ni catalysts, leading to catalyst deactivation or plugging of the reactor. A high dispersion of metal species over the catalyst9 or incorporating alkali metal or alkaline earth metal oxides into the catalyst10 may reduce coke formation. The stability of Ni catalysts may be improved by the addition of basic supports or promoters. In recent work, it has been found that the addition of alkali metals (Na, K, and Li) modifies the Ni active phase by suppressing deactivation by carbon formation.11,12 In particular, catalysts composed of Ni doped * To whom correspondence should be addressed. Fax: +98 (21)77240495. E-mail: [email protected].

with Li13 have been reported to show very promising potential for application in fuel-cell reactors (molten carbonate fuel cell, MCFC) for the production of synthesis gas from methane and carbon dioxide. Elsewhere, the role of K in carbon-free dry reforming of methane has been investigated.11 In this work, the effects of the alkali metals Li, Na, and K on La-Ni-Al systems have been investigated. In previous studies,5 LaNi0.3Al0.7O3 was found to be the best structure for methane reforming, showing good catalyst performance. This efficacy stemmed from highly dispersed and stabilized Ni metal particles on the perovskite surface. 2. Experimental 2.1. Materials. Mixed-oxide catalysts of the type MxLa1-xNi0.3Al0.7O3-d (M ) Na, Li, and K; x ) 0, 0.2, 0.5, 0.8, and 1.0) were prepared by a sol-gel method using propionic acid as solvent. Precursor solutions were separately prepared by dissolving the raw materials in hot propionic acid. The reagents used were lanthanum nitrate hexahydrate La(NO3)3 · 6H2O, aluminum nitrate nonahydrate Al(NO3)3 · 9H2O, nickel nitrate hexahydrate Ni(NO3)2 · 6H2O, potassium nitrate KNO3, sodium nitrate NaNO3, and lithium nitrate LiNO3. All of the starting compounds were of purity >99%. 2.2. Perovskite Preparation. The initial source of the metallic element was separately dissolved in the minimum volume of hot propionic acid until the formation of a limpid solution (at P ) 1 atm and T ) 90 °C). After dissolution, the four solutions were mixed and stirred (at P ) 1 atm and T )130 °C) for 120 min. Thereafter, the propionic acid was distilled in a reflux process until the formation of a resin, which hardened on cooling. The resulting gel was dried at 90 °C overnight and then calcined at 700 °C for 4 h.5 A scheme for the sol-gel preparation is illustrated in Figure 1. Catalysts were calcined by increasing the temperature at a rate of 3 °C/min from room

10.1021/ie800111e CCC: $40.75  2008 American Chemical Society Published on Web 07/22/2008

Ind. Eng. Chem. Res., Vol. 47, No. 16, 2008 5893 Table 2. Comparison between Before and After Theoretical and Analytical (EDS) Perovskite Chemical Analysis M/La

Ni/Al

analytical analytical perovskite structure theoretical before after test theoretical before after test Na202 Na205 Na208 Na210 K302 K305 K308 K310

Figure 1. General preparation of perovskite catalysts by a sol-gel process. Table 1. Cods Used for Catalysts with Formula MxLa1-xNi0.3Al0.7O3-d perovskite

x)0

x ) 0.2

x ) 0.5

x ) 0.8

x)1

LixLa1-xNi0.3Al0.7O3-d NaxLa1-xNi0.3Al0.7O3-d KxLa1-xNi0.3Al0.7O3-d

Li100 Na200 K300

Li102 Na202 K302

Li105 Na205 K305

Li108 Na208 K308

Li110 Na210 K310

temperature in a static air atmosphere. Table 1 shows the data codes for the catalysts prepared in this study. 2.3. Characterization of the Perovskites. The structures of the resins obtained following the gel formation process and the formation of precursors in the propionic acid solution were studied by means of IR spectroscopy (3 wt % in a KBr matrix) using a Shimadzu-8400S spectrophotometer. All samples were chemically analyzed by SEM in conjunction with EDS to determine their compositions. SEM images were acquired with a Philips XL30 microscope. EDS analysis was

Figure 2. Experimental setup.

0.041 0.165 0.661 0.070 0.281 1.127 -

0.031 0.170 0.881 0.051 0.252 1.339 -

0.038 0.185 0.779 0.061 0.228 1.230 -

0.932 0.932 0.932 0.932 0.932 0.932 0.937 0.932

0.921 0.864 0.988 0.905 0.907 0.957 0.999 0.910

0.890 0.826 0.923 0.937 0.927 0.915 0.959 0.950

carried out using a DS DX-4 analysis system. An accelerating voltage of 30 kV was applied. The crystalline phases and lattice parameters in the samples were determined by XRD analysis. Data were collected at room temperature using a Philips PW-1800 diffractometer employing Cu-KR radiation (λ ) 1.5406 Å) and operating at 40 kV and 30 mA. Specific surface area measurements were carried out by the BET method based on N2 physisorption capacity at 77 K on a Micromeritics Flowsorb apparatus, the instrument operating in single-point and multipoint modes. Prior to analysis, samples were degassed at 150 °C for 2 h. TPR studies were performed with a Micromeritics PluseChemiSorb 2705 apparatus equipped with a thermal conductivity detector (TCD). The experiments were conducted on samples of the calcined catalysts weighing approximately 50 mg. The samples were initially flushed with Ar (50 mL/min) as the temperature was increased at a rate of 10 °C/min to 200 °C, where it was held for 60 min to remove water. Then, 5.1% H2 in Ar (50 mL/min) was introduced with a rate of heating of 10 °C/min from room temperature to 1000 °C and was maintained for 70 min. The TCD determined the amount of hydrogen consumed. The amount of carbon deposited on each catalyst after the reaction was quantified by carbon analysis using a Leco CS444 thermal analyzer. Samples were heated from ambient temperature to burning in an oven, and the amount of gas produced was determined by means of a quadruple mass spectrometer. 2.4. Evaluation of Catalytic Performance. Catalytic tests on methane reforming to produce syngas were performed at atmospheric pressure. The reaction conditions applied were as follows: fixed-bed stainless steel reactor (6.6 mm internal

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Figure 3. XRD analysis of the catalyst for MxLa1-xNi0.3Al0.7O3-d solid oxide (A) before and (B) after dry reforming. Dashed line and “P” is the perovskite phase.

diameter); inlet temperature, 500-800 °C; relative flow rates of the components, CH4:CO2:N2 ) 1:1:8; total flow rate, 50 mL/min; weight of catalyst, 200 mg. The experimental installation is depicted in Figure 2. The fixed-bed stainless steel reactor, which was placed in a cylindrical ceramic oven, was fed up-flow. Temperature controllers regulated the temperature of the catalyst bed. One thermocouple was placed at the bottom of the catalyst bed, while another one allowed measurement of the temperature 5-10 mm above the bed. The products, feed, and gas mixtures were analyzed by online gas chromatography using a Thermo Finnigan KAV00109 setup (TCD; helium carrier gas, Propack-Q and 5 Å molecular sieves, 60/80 mesh). The temperature program consisted of an initial treatment and three cycles. The initial treatment consisted of a temperature increase from room temperature to 500 °C. During this step, no synthesis gas formation was observed for each catalyst. The first cycle was formed by a continuous increase of temperature from 500 to 800 °C at a rate of 3 °C/min and by a stepwise decrease every 50 °C down to 500 °C (one GC analysis at each stage). The second and third cycles were comparable to the first except that the initial temperature was 500 °C. The catalyst was cooled rapidly to room temperature.

Table 3. Structural Properties of the Catalysts perovskite structure

multipoint (BET) m2/g

pore volume (cm3/g)

volume adsorbed (cm3/g)

lattice parameters experimental (Å)

Na205 Na208 K305 Li102 LaNi0.3Al0.7O3

7.1656 4.4139 4.955 3.2062 15.2495

0.0102 0.0076 0.0078 0.0037 0.054

6.620 4.939 5.026 2.747 4.87

3.8150 3.8155 3.8208 3.8267 3.8100

3. Results and Discussion 3.1. Structures of the Perovskite Catalysts. Characterization of the samples by FT-IR spectroscopy showed that the use of propionic acid as solvent and metal nitrates as starting salts led to the successful production of solid oxides with the perovskite structure as there was no precipitation or reaction between the propionic acid solvent and the La(NO3)3, Al(NO3)3, Ni(NO3)2, KNO3, NaNO3, or LiNO3 starting salts. All metallic elements in the starting salts were incorporated into the propionate structure and were homogeneously distributed therein. Gels produced from the individual starting salts and mixtures thereof were investigated, and all of them showed peaks at around 1433 cm-1 (bidentate propionate peak) and 1570 cm-1 (monodentate propionate peak). Nitrate peaks at around 830 and 1380 cm-1 and a propionic acid peak at around 1468

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Figure 4. TPR curves of MxLa1-xNi0.3Al0.7O3-d solid oxide.

Figure 5. Hydrogen consumption for MxLa1-xNi0.3Al0.7O3-d solid oxide.

cm-1 coexisted for all of the nitrate salts, even after prolonged aging of the gels. Table 2 lists the results of chemical analyses of the eight synthesized mixed-oxide perovskites before and after the reactivity tests. For comparison, the average theoretical (EDS) compositions have also been calculated from the degree of substitution indicated by the M/La ratio and the Ni/Al ratio of the cations in the B-sites of the perovskite. Good agreement was observed between the theoretical and analytical (EDS) perovskite compositions for each MxLa1-xNi0.3Al0.7O3-d series, whereas slight differences in the elemental compositions before and after the tests can probably be ascribed to differences in the stoichiometries with regard to oxygen. Indeed, the value of x strongly depends on the preparation conditions and has not been precisely measured. The data are consistent with the finding from the FT-IR data that all elements are incorporated into the propionate structure. Therefore, the respective ratios of the elements are close to the actual ratios. It could be concluded that the chosen structures showed good dispersion of all of the elements, and lower coke formation was thus expected for these structures. The perovskites have been mainly characterized by XRD, and all of them show a main diffraction peak in the range 32° < 2θ < 33°. A trimetallic structure was not obtained. Rather, LaNiO3 and LaAlO3 structures were formed. The formation of a trimetallic structure is directly related to the initial presence of nitrates and to the competition between bimetallic (LaNiO3 and LaAlO3) and trimetallic perovskite formation. For trimetallic La-Ni-Al systems, a progressive and regular shift of the structure peaks between those of LaNiO314 and LaAlO315 with increasing x has been noted. An expansion of the 2θ diagram between 32° and 33° shows this progressive shift for the most intense diffraction peak of the LaNixFe1-xO3 structures.16 For

MxLa1-xNi0.3Al0.7O3-d (M ) Li, Na, K), when x ) 1, no perovskite structure is formed, whereas for all other members of the series, the perovskite structure is the main phase detected in the XRD patterns. As shown in Figure 3A, all catalysts that were calcined at 750 °C show sharp peaks attributable to the LaNi0.3Al0.7O3 perovskite structure. Small shifts of the main peaks stem from the incorporation of the alkali metal cations into the structure. Close inspection of the XRD patterns showed that the main peaks are shifted in a regular manner. That is to say, on substituting lanthanum by alkali metal cations, the main peak position increased linearly from 33.02° to 33.16° for sodium, to 33.08° for potassium, and to 33.04° for lithium. However, in the case of MxLa1-xNi0.3Al0.7O3-d with x ) 0.8, some peaks in the XRD pattern were indicative of the presence of alkali metal oxide in the structure. Consequently, x in these structures was not exactly 0.8. For comparison, XRD patterns of the samples after they had been used in 15 h activity tests at 500-800 °C are shown in Figure 3B. No specific differences between the XRD patterns before and after the reactivity tests are evident, although in some cases the intensity of the alkali metal oxide peaks Na208, K308, and K305 was seen to increase. It seems that perovskites with a higher lanthanum content are more stable. Some physical properties of the studied samples are reported in Table 3. All fresh samples have a low specific surface area, but their surface areas depend on the calcination temperature. Most of the synthesized solids showed surface areas lower than 20 m2/g; however, those of the lithium series showed the lowest values, while those of the sodium series showed the highest values. The surface areas of all samples are lower than the area of LaNi0.3Al0.7O3. A low surface area is highly favorable for dry reforming because a high surface area suppresses the main reaction to a side reaction. It seems that lanthanum substitution by lithium, potassium, and sodium alone produces lower surface areas (less than 10m2/g). Table 3 lists the BET surface areas, obtained in multipoint modes, pore volumes, and volumes adsorbed of some of the best catalysts. In addition, lattice parameters for some of the best catalysts are reported in Table 3. Assuming a pseudocubic structure, the lattice parameter (a) could be calculated for each value of x taking into account the six most intense diffraction peaks. The results confirmed the formation of a solid M-La-Ni-Al solution and that the variation in the lattice parameter may be used to define the alkali metal contents for each of the obtained perovskites and, in particular, to evaluate the alkali metal contents after the reactivity tests, as corroborated by the EDS results. This is of great importance for the stability and reactivity of the structures, as we shall see later. The results of temperature-programmed reduction (TPR) studies on the perovskites are shown in Figure 4. The active species in the reforming of methane are reduced Ni particles on the surface of the catalysts. It has also been suggested that strong interactions between reduced metals and main structures are important in preventing sintering of the Ni particles. Accordingly, studies of the reducibility of Ni oxides are of prime interest. For all MxLa1-xNi0.3Al0.7O3-d catalysts, except sample K308, two main peaks were observed at two temperatures. It has previously been shown17 that LaNiO3 is reduced in two stages and that LaAlO3 is almost irreducible up to 900 °C, so that the first peak indicates reduction of Ni3+ to Ni2+ and the second peak indicates reduction of Ni2+ to Ni0, which is favorable for the methane-reforming reaction. The stability of the perovskite structure is shown with the second reduction peak. The high temperature of the second reduction peak characterizes

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Figure 6. SEM analysis of the catalyst for Na205 solid oxide (A) before and (B) after dry reforming.

a strong interaction between Ni and the perovskite or the support. This strong interaction is probably one of the reasons for the high resistance to coking and the good aging of the perovskite catalysts because separation of nickel molecules and their migration and sintering has been eliminated. In this regard, as mentioned in previous work, the temperature of maximum hydrogen consumption for the second reduction peak gives a good figure for stability and low coke formation of the catalyst during the reaction.14 At low La substitution, i.e., x e 0.5, two reduction peaks are seen at distinct temperatures, but at higher substitution, as in K308, the two peaks are closer together. With x ) 1, the two peaks merge to form one peak, whereas for Na208, the two peaks are well separated, with the second peak being observed at a much higher reaction temperature of 966 °C. Thus, Ni0 particles are produced only at a higher temperature. Catalyst Na205 is slowly but continuously reduced between 544 and 620 °C. A second reduction step is seen at a higher temperature range of 711-790 °C. TPR results for the present MxLa1-xNi0.3Al0.7O3-d systems have indicated that increasing reaction temperature (500-800 °C) provides more active surface-bearing M, Ni, and Al metals, resulting in an increased conversion of CH4 into syngas. A thermal conductivity detector was used to analyze the effluent gas following passage through a water trap, which enabled quantification of the hydrogen consumption. The total amount of hydrogen consumption was determined by comparison of the different surfaces, but instantaneous data could not be deduced. Hydrogen consumption during reduction of the different samples was in good agreement with the calculated values. The errors are between 3 and 20%, which means the real structures are similar to the expected structures. Figure 5 shows a comparison of calculated and experimental data for H2 consumption. As is evident from Figure 5, the calculated number of moles of hydrogen required for complete reduction of Ni3+ to Ni0 in MxLa1-xNi0.3Al0.7O3-d systems compares well with the hydrogen consumption measured in the TPR tests. The high-temperature reduction peak is indicative of a strong interaction between M, La, Ni, and Al in the perovskite structure. This result confirms the purity of the perovskite phase present in the sample with x ) 0.5; indeed, as has been noted previously, this strong interaction is probably one of the reasons for the good resistance to coking and the good stability of the mixed M-La-Ni-Al perovskite catalysts. Consequently, all of the reduced perovskites are stable under reducing conditions at around 750 °C. This stability of the reduced oxides would allow their use as stable catalysts for the production of syngas through

methane reforming. In order to estimate the homogeneity of the solid solutions obtained, the MxLa1-xNi0.3Al0.7O3-d systems were examined by SEM. SEM micrographs of Na205 samples, before and after the reactivity tests, are shown in Figure 6. It can be seen that substitution with sodium leads to porous structures in agreement with the amount of nitrogen adsorption and pore volume reported in Table 3. Holes are formed during calcination due to the decomposition of nitrates with the elimination of NO2. Hence, the presence of nitrate in the starting salt would seem to favor the generation of holes. 3.2. Catalytic Activities of the Perovskite Catalysts. In previous studies, the effects of partial substitution of the B-site cations in LaNiO3, i.e., the nickel, have been investigated. It was found that partial substitution of nickel by aluminum led to changes in the reducibility and the stability of the structure under the reaction conditions and limited the migration of the active nickel; however, stability depends on the degree of nickel substitution. The catalyst LaNi0.3Al0.7O3 showed good stability and aging in dry reforming over 170 h.5 The study was started with LaNi0.3Al0.7O3, and the effect of partial substitution of the A-site cations on activity in methane dry reforming was investigated. It was demonstrated that partial substitution of lanthanum by alkali metal cations decreased coke formation, while the catalyst performance remained good. The catalytic performance of MxLa1-xNi0.3Al0.7O3-d solid oxide in dry reforming at different temperatures was studied. The best results are presented in Figure 7. As shown in Figure 7A, methane conversions of up to 90% and hydrogen selectivities of up to 70% were obtained at 750 °C and 1 atm. Hydrogen yield and H2/CO ratio in dry reforming are illustrated in Figure 7B, which shows a good yield and an H2/CO ratio near to 1. Figure 7C presents CO2 conversions and CO selectivities that show the best results for Na205. Thus, on replacing lanthanum with alkali metal cations, the catalytic performance remained good. However, as the lithium or potassium content of the perovskite was increased, the catalyst showed lower catalytic activity at the same temperature. This finding is consistent with the results of the TPR experiments, which showed that reduction required a higher temperature with these perovskites. Meanwhile, the selectivity in favor of syngas production was almost unchanged because it is only dependent on the relative surface concentration of the alkali metal cations and the La-Ni-Al structure, which is related to the alkali metal content in the perovskite precursor lattice. Thus, partial substitution of lanthanum by sodium showed the best CO yield. As can be seen in Figure 8, the yield of CO was maximized at x ) 0.5; on the

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Figure 8. Percentage of CO yield for NaxLa1-xNi0.3Al0.7O3-d versus x in methane dry reforming at 650, 700, and 750 °C.

Figure 9. Catalytic performance of Na205 for dry reforming in different temperatures.

Figure 7. Catalytic performance of MxLa1-xNi0.3Al0.7O3-d solid oxide for dry reforming: (A) percentage of conversion of CH4 and selectivity of H2; (B) yield of H2 and H2/CO ratio in different temperatures; (C) percentage of conversion of CO2 and selectivity of CO.

other hand, the catalytic performance of LaNi0.3Al0.7O3 was improved by partial substitution of La by Na such that these elements were present in equimolar amounts (La/Na ) 1). Of the results obtained, Na205 gave an H2/CO ratio closest to 1 and good performance. As demonstrated in Figure 9, methane conversions of up to 90%, hydrogen selectivities of up to 80%, hydrogen yields of up to 80%, and an H2/CO ratio near to 1 were obtained at 750 °C at atmospheric pressure. CH4 conversion of Na205 for dry reforming during three cycles is indicated in Figure 10. All of the catalysts showed good stability during 15 h reactivity tests. Therefore, it was clear that Na205 showed the best catalytic performance, and a direct relationship between the overall activity as well as synthesis gas productivity, selectivity, and H2/CO ratio versus time on stream for dry reforming at 750 °C is essentially demonstrated in Figure 11.

Figure 10. CH4 conversion of Na205 for dry reforming during three cycles.

However, the lowest amount of coke formation was found for the Li102 structure (less than 1%). The amount of coke formation, indicated by the carbon deposited on each catalyst after the reaction, was quantified by carbon analysis. Samples were heated from ambient to combustion temperature in an oven, and the amount of gas produced was determined by means of a quadruple mass spectrometer. All solid solutions showed low amounts of coke formation during the 15 h reactor test. Figure 12 shows the percentages

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EDS and SEM analyses showed good homogeneity of the prepared systems. Reactivity tests showed that Na205 displays the best performance for methane reforming with carbon dioxide. This catalyst produced an H2/CO ratio close to 1 over a wide temperature range. These interesting properties are favorable for the application of these mixed perovskite systems as catalysts giving high conversions, selectivities, and yields. However, the lowest amount of coke formation was found for the Li102 structure (less than 1%). Literature Cited

Figure 11. Catalytic stability of Na205 for dry reforming at 750 °C.

Figure 12. Percentage of carbon in (A) Li102, (B) Na208, (C) K305, (D) Na205, and (E) LaNi0.3Al0.7O3.

of carbon in Li102, Na208, K305, Na205, and LaNi0.3Al0.7O3. In contrast, a higher degree of coke deposition occurred on LaNi0.3Al0.7O3 (about 8.71%), and the lowest amounts of coke formation were found for the Li102 catalyst (about 0.71%), which shows that the addition of Li in the structure further increases the basicity of the catalysts, though the amount of carbon decreased with increasing lanthanum substitution (about 5.99 for Na205 and about 0.81 for Na208). However, Na208 shows lower H2 selectivity and yield than Na205 (Figure 12). 4. Conclusions Catalysts having an MxLa1-xNi0.3Al0.7O3-d perovskite structure (M ) Li, Na, K; 0 < x < 1) have been obtained by means of a sol-gel method using propionic acid as the solvent. These structures have been shown to exhibit good efficiency in catalyzing dry reforming reactions. FT-IR analysis has shown nitrate salts to be a good choice as raw materials for the catalysts, and all starting salts were incorporated into the propionate structure. Characterizations by XRD have demonstrated the formation of MxLa1-xNi0.3Al0.7O3-d mixed oxides of the perovskite structure, except for x ) 1. In addition, the results of

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ReceiVed for reView January 21, 2008 ReVised manuscript receiVed June 5, 2008 Accepted June 24, 2008 IE800111E