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In large-scale industry, the WGS reaction is the most widely used method for the purification of hydrogen obtained from natural gas. This is a process that hinges on factors such as temperature, pressure, type of catalyst, etc. In this work, copper-based solids were obtained from hydrotalcites, which were characterized through various techniques and evaluated within the WGS reaction at different temperatures. Hydrotalcite-type precursors displayed thermal behaviors that depend on their composition, whereby higher temperatures become necessary for the collapse of the HTLc structure in the solids with higher zinc and aluminum content. The calcination of precursors led to the formation of CuO particles in all the materials, which were more resistant to the reduction processes as the aluminum content augmented. The catalysts were active in the reaction under study with C0.50Z0.25A0.25 being the most active material due to the higher content of metallic copper on the surface. The most effective material in terms of metallic copper content present on the surface was C0.33Z0.33A0.33, in which the occurrence of CuO was not evinced after its use, in addition to displaying the smallest particle size of Cu0 as well as, possibly, the existence of Cu–Zn interactions on the surface.

This study investigated the effect of the partial substitution of Ti by Mg on the La2Ti2O7 perovskite-type structure towards improvements in the selective results of OCM reactions. The LaTi1−xMgxO3+δ catalysts were prepared with x = 0, 0.25 and 0.50 according to a polymer complexing method. XPS analysis showed a surface reconstruction with Mg addition, increasing the formation of oxygen vacancies in the interface formed by La–O–Mg and with an Mg-enriched surface compared to bulk compositions. DRIFTS results presented spectra more restricted to mono- and bidentate carbonate bands with the Mg load increasing, which significantly influence the OCM reaction. Differences in the M–O bonding force were demonstrated by XPS, FTIR, and Raman analysis, which result in the change of the catalyst basicity with the Mg addition. The M–O bond force constants (k) were calculated and showed a linear correlation with C2 selectivity. The catalytic results showed that methane conversion and C2 selectivity increased as a function of the Mg amount. Changes in the reaction conditions confirmed that both CH4/O2 feed ratio and reaction temperature are important parameters for the OCM reaction. The best catalytic reaction conditions were WHSV = 30 000 mL gcat−1 h−1, CH4/O2 = 8 and T = 800 °C for LaTi0.5Mg0.5O3 (LTMO-50) catalyst, which achieved 51.4% C2 selectivity. The catalyst remained thermally stable under such conditions even after 24 h of reaction, which has proven the advantage of Mg substitution in this catalyst structure.

Comparative research about the total CO oxidation and CO-PROX reaction over Au-based materials supported on different oxides was carried out. CeO2, MnO2, TiO2 and SiO2 with nominal content of 1 wt.% of Au were prepared by a modified deposition–precipitation method. The samples were characterized by XRF, XRD, BET, H2-TPR and HR-TEM techniques. Catalytic results of the CO oxidation in the absence and presence of hydrogen showed that the supports and Au/SiO2 were inactive. For the Au/MnO2 and Au/TiO2 samples, CO conversion was lower in the presence of H2, while for Au/CeO2 the conversion of CO in the CO-PROX was higher compared to that in the total CO oxidation. These results show that the impact of H2 on CO oxidation over Au catalysts is dependent on the charactersitics of the materials that, in turn, are influenced by the nature of the support.

CuO/CeO2 catalysts were prepared by the Pechini method and applied in the CO preferential oxidation (CO-PROX). The CuO content effects on the catalysts and the presence of H2O and CO2 in the reaction stream on the catalytic performance were investigated. The catalyst with 1.0 wt.% CuO presented the highest conversion and selectivity in the COPROX in the temperature range 100–250 °C. It was observed that the catalytic system is sensitive to the dispersion of the active phase and, independently of the copper content, the high activity of the CuO/CeO2 catalysts is closely related to the finely dispersed CuO species strongly interacting with CeO2 support. In the long-term stability test under the real CO-PROX condition with 10 mol% H2O and 15 mol% CO2 in the reactant stream, about 90% CO conversion can be maintained even at low temperature (150 °C) with 95% selectivity.

MgAl hydrotalcite was successfully prepared through the sol-gel method and modified by in situ addition of base metals (Me = K, Ba, Sr and La). The Me–MgAl hydrotalcites were calcined and the obtained oxides were evaluated as catalysts for ethylic transesterification in order to investigate their potential application for biodiesel production. The Me–MgAl characterization revealed that the materials present different crystalline structures and the metal addition caused surface area reduction and increased the apparent crystallite size. On the other hand, the addition of the base metals to hydrotalcite deeply affected the base properties of the oxides, increasing their catalytic activity. Particularly, the Ba–MgAl presents the highest amount of strong base sites which resulted in a high conversion (≈90%) in the model transesterification reaction between methyl acetate and ethanol. Furthermore, an ester conversion of about 80% was reached in soybean oil transesterification. Moreover, the Ba–MgAl can be reused for 3 batch cycles with low deactivation. These results suggest that Ba–MgAl can be considered a promising heterogeneous catalyst for biodiesel production.

Considering that the combination of ZrO2 and CeO2 have superior catalytic properties compared to the individual oxides, the present work investigates the production of light hydrocarbons by carbon dioxide hydrogenation at atmospheric pressure, using iron catalysts constituted of CexZr(1-x)O2 solid solutions (x = 0, 0.25, 0.5, 0.75, and 1). The aim was to determine the effect of the composition of the CexZr(1-x)O2 oxides on the reaction. The materials were characterized by XRF, XRD with Rietveld refinement, textural analysis, Raman spectroscopy, H2-TPR, H2-TPD, and CO2-TPD. The catalysts were tested in the CO2 hydrogenation reaction at 370 °C, under atmospheric pressure, using a molar ratio H2/CO2 = 3, for at least 5 h of time on stream. For the iron-based catalysts constituted of CeO2 and/or ZrO2, the CO2 conversion and selectivity towards the light olefins first increased as the Zr content increased, reaching the highest values with the iron catalyst supported on the material containing 50 % of Ce and 50 % of Zr (molar concentrations on an oxygen-free basis), and then decreased at higher Zr concentrations. The highest CO2 conversion achieved with this catalyst could be attributed to the quantity of basic sites. An appropriate balance between the amounts of adsorbed CO2 and H2 could provide a suitable surface C/H concentration ratio, leading to the best products distribution.

A strategic option for the production of H2 from renewable resources is use of the ethanol steam reforming reaction. Catalysts based on nickel have been widely investigated for this reaction, offering the advantages of low cost and high activity. However, a difficulty is that nickel may be strongly deactivated by coke formation. Perovskite-type mixed oxides are promising precursors for nickel-based catalysts, since their reduction leads to the formation of highly dispersed metal particles that can mitigate carbon deposition. However, high calcination temperatures are required for perovskite structure formation, resulting in low surface areas and limiting the effectiveness of this method. In order to address this difficulty, the present work proposes a novel strategy whereby the perovskite-type oxide LaNiO3 is supported on SBA-15. Characterization of the catalysts was performed using XRF, XRD, SEM, TPR, TEM, BET, H2-TPD, and TGA techniques. Their performances were then evaluated in catalysis of the ethanol steam reforming reaction to produce hydrogen. Calcination at 750 °C resulted in formation of highly dispersed perovskite on a support that presented high specific surface area. The catalyst obtained from reduced LaNiO3/SBA-15 with 33 wt% perovskite was the most active in the reaction. Analyses using TGA and SEM showed the formation of carbon mainly over Ni catalysts obtained from bulk LaNiO3 perovskite, while supporting LaNiO3 on SBA-15 led to lower deposition of carbon. The superior performance of this material in catalysis could be attributed to the dispersion of the perovskite on SBA-15, resulting in smaller size of the Ni metal particles formed during the reduction, compared to the catalyst derived from bulk perovskite. This promising method could be used in the production of a wide range of other catalysts.

(SrxLa1-x)CeO mixed oxide catalysts were prepared using the sol-gel method, with a non-ionic surfactant as a soft template for a porous structure. The use of nitrogen physisorption measurements, BJH pore size distribution curves, and SEM micrographs confirmed improvement of the porous texture of the mixed oxide catalysts, compared to catalysts synthesized by a conventional method. X-ray diffraction and Raman spectroscopy analyses demonstrated that the preparation method led to different crystalline structures in the catalysts. In the oxidative coupling of methane (OCM) reaction, use of the catalyst prepared with the soft template improved C2 yield, C2 selectivity, and C2H4 selectivity by approximately 65, 101, and 130%, respectively. The addition of 0.2 Sr content in the porous catalysts also provided gains of approximately 63, 46, and 85% in C2 yield, selectivity for C2, and selectivity for C2H4, respectively, when compared to the Sr-free catalyst. The satisfactory performance of the catalyst with 0.2 Sr content was probably due to the improved textural properties that provided a surface composition with concentration of Ce3+ of 59.3%. Based on statistical modeling of variables such as temperature, CH4/O2 ratio, and WHSV, it was possible to obtain a C2 yield of 16.2%, C2 selectivity of 76.2%, and C2H4 selectivity of 50%.

Nickel supported on MgAl2O4 spinel (Ni/MA) and the effects of X-ZrO2 (X = Ce, La, Sm and Y) addition to the support were studied in Methane Tri-Reforming (MTR) process. The characterization techniques employed were XRD, B.E.T., H2-TPR, H2-TPD, CO2-TPD, XPS, and in situ XANES. The presence of lanthanides and Y associated to ZrO2 modified the Ni0 dispersion and the surface basicity. These properties influence the coke formation, which increased as the metallic dispersion diminished. Ce-ZrO2 association on the spinel support led to the greatest catalytic performance, increasing reactants conversions due to its adequate base properties that allowed the adsorption of new reactants molecules due to coke elimination, associated to its smallest apparent Ni0 average size. Moreover, the Ce-Zr support favored the NiO activation, without compromising the nickel dispersion.

The preferential oxidation of CO (CO-PROX) is promoted at the interface between CuO and CeO2. For this reason, different synthesis methods of CuO/CeO2 catalysts have been investigated in order to maximize this interface. However, the understanding of the effect of CuO/CeO2 catalysts preparation method on the redox properties and CO-PROX reaction performance is still unclear. In the present work, 2 wt% CuO/CeO2 catalysts were prepared by four synthesis methods, namely co-precipitation with ammonium hydroxide (CP), deposition-precipitation with ammonium hydroxide (DA) or urea (DU), and impregnation (IM). The materials were characterized by XRD, SEM-EDS, H2-TPR, REDOX cycles, N2O passivation and applied to the CO-PROX reaction. The catalytic performance of the investigated materials was evaluated by the TOF values of CO oxidation. CuCe (CP) and CuCe (DU) catalysts were the most stable in terms of redox properties and the most active in the CO-PROX reaction. On the other hand, the CuCe (DA) catalyst presented the least stable behaviour during the redox cycles and the worst performance in CO-PROX reaction. These results clearly show that the stability of the CuO/CeO2 interface, submitted to successive redox cycles, plays a significant role towards the CO-PROX reaction and that this stability depends on the employed synthesis method.

Nickel catalysts supported on magnesium aluminate promoted with ZrO2, CeZrO2 and CeO2 were evaluated under methane tri-reforming reaction. MgAl2O4 synthesis was assisted by P123® surfactant, assuring high porosity. The catalysts were tested at 650 °C and 750 °C. Zr and Ce Zr promoted catalysts showed less coke deposition and increased conversions, mainly at 750 °C, while the non-promoted catalyst featured lowest reactants conversion due to an unstable performance caused by filamentous coke deposition. The H2/CO ratio produced at 750 °C was at around 2, suitable to FT synthesis. In situ XPD analysis suggested nickel remained active as Ni0 throughout the reaction, even in the oxidant environment, containing water and oxygen, and high-temperature exposure. Considering that nickel oxidation during the process is one of the concerns related to the catalyst deactivation during tri-reforming of methane, along with carbon deposition, these catalysts are promising to active and stable syngas production.

This study investigates the influence of ionic liquid in morphology, acid-base properties, metal dispersion and performance of 5%Ni/ZrO2 catalysts in the methane tri-reforming reaction. Zirconia was prepared by precipitation and the catalysts by wet impregnation. The ionic liquid modified the acid and basic character of the catalysts and positively influenced the methane tri-reforming reaction efficiency. The reaction was evaluated with synthetic biogas and with stoichiometric feed molar ratio (CH4: CO2: H2O: O2 = 1:0.5:0.5:0.1 and CH4: CO2: H2O: O2 = 1:0.33:0.33:0.16). The Ni/ZrO2 prepared with ionic liquid exhibits promising catalytic activity and stability in methane tri-reforming at 800 °C in 4 h run, without coke formation. An increase in the reaction temperature results in an increase of hydrogen yield and the methane conversion, reaching ∼85% at 850 °C. The presented results demonstrate that the tri-reforming reaction could be used for production of syngas with H2/CO ratio appropriate for methanol synthesis.

The electrocatalytic CO2 reduction reaction (CO2RR) is a promising strategy for producing multi-carbon compounds using only CO2 and H2O at room temperature. Significant advances have already been achieved in understanding how some characteristics of copper electrodes, the current state-of-the-art catalyst for multi-carbon formation via CO2RR, affect the product spectrum. Advances and insights have been reported for, among others, the effect of crystallographic orientation, active surface area, and composition of M-copper (M = Au, Ag, Zn, etc.) materials, and how these alter the distribution of CO2RR products. However, a systematic study evaluating the significance of these variables in the CO2RR to C2+ products is still lacking in the literature and represents an important step in the development of new materials with optimized properties that can be more selective to C2+ compounds. In this paper, we have systematically investigated the effect of the roughness factor, chemical composition, and surface morphology of CuxZny electrocatalysts on the product distribution during CO2RR. Firstly, Cu, Cu90Zn10, and Cu75Zn25 electrodes were exposed to oxidation-reduction cycles to produce Cu and CuxZny electrodes with different morphologies, roughness factors, and chemical composition. Our results show that an increase in the roughness factor and Zn content lead to higher faradaic efficiency (FE) to C2+ products. Furthermore, the influence of the nanoscale morphology is imperative for the production of C2+ compounds. Specifically, nanocubes of Cu and CuxZny presented the highest FE to C2+ products among the different surface morphologies studied in this work (polished flat surface, nanosheres, nanocubes, nanodendrites, and nanocauliflowers), showing that CC coupling during CO2RR is mainly shape dependent.

Properties of co-precipitated CuO/CeO2 catalysts with nominal content of 1–3 wt.% copper were investigated by EDS, XRD, BET, STEM, EDS map, H2-TPR, in situ DRIFTS and in situ XANES. By comparing results of DRIFTS, XANES and catalytic performance in the CO-PROX reaction, it was evidenced a relationship between the catalytic behavior and the copper oxidation state of the materials. In situ DRIFTS and XANES analyses shed light on the oxidation state of active copper species involved in the CO-PROX reaction between 120 °C and 200 °C. The investigated catalysts present a balance between Cu° and Cu+ species under PROX conditions and the Cu+ is the main species liable to adsorb CO. Furthermore, our studies indicated that the PROX reaction on CuO/CeO2 is impacted by the nature of Cu species, which in turn may vary with reaction temperature, depending on the Cu content. From these results, we propose a new mechanism of PROX reaction on CuCe catalysts, including Cu°/Cu+ and Ce3+/Ce4+ redox pairs and direct CO oxidation on Cu°.

In the present work, we investigated the influence of the synthesis method of Nb-promoted Cu/Zn materials on their physicochemical and catalytic properties. Cu/ZnO/Nb2O5 was prepared by coprecipita...

The development of society is dependent on commodities such as fuels and chemical feedstock. Most of these commodities are obtained from oil as raw material. Although the need to find a friendly solution to couple an economically viable energy model with a greener solution, it is known that technologies applying renewable sources are in an early stage of development. The conversion of methane into clean fuels or chemical feedstock with high commercial value, such as hydrogen, ethylene, or methanol is interesting from the energetic and economic point-of-view. Among the methods of methane conversion, the industrially used is the steam reforming (MSR), in which methane reacts with water to produce syngas, a mixture of CO and H2. Nevertheless, this reaction is highly endothermic and responsible for a large volume of CO2 emitted by the reactor burners that provide energy to the reactors. An interesting alternative process for methane conversion is the dry reforming of methane (DRM), which consists of the reaction of methane with CO2, also yielding syngas. The advantage of this reaction is the utilization of two harmful gases to the atmosphere. The disadvantage of this reaction is due to the catalyst deactivation by carbon deposition. In heterogeneous catalysis, there is a strong relationship between catalytic performance and surface and textural properties, that are outlined by the number and distribution of available active sites. In this way, different synthetic routes may be used to design these properties and obtain products of commercial interest, such as ethylene. The commercial production of ethylene occurs by the recuperation of refinery gases, thermal cracking of light hydrocarbons, mainly ethane and propane, or a combination of both processes. An alternative process of ethylene production may be from natural gas and or biogas. This process can be performed by the syngas route or by oxidative coupling of methane (OCM). The first process is an indirect conversion of methane and involves several steps, which increases the process costs. The second one is a direct conversion, where methane is directly converted into C2 (ethane and ethylene) hydrocarbons. Although the OCM is not yet a reaction on an industrial scale, several efforts are being made to design a catalytic system to achieve C2 hydrocarbons yields above 30%, the minimum required. Besides that, another technology has been studied to directly produce ethylene via the oxidative coupling of methane using CO2 as a mild oxidant (CO2-OCM). These technological routes for the valorization of methane and CO2 will be addressed in this review.

Ni-Ga alloy catalysts were synthesized by a surfactant-assisted co-precipitation method and were tested in CO2 hydrogenation to methanol at 10 bar and at ambient pressure. The presence of surfactant in the synthesis led to a decrease in particle size, with the catalyst produced using 1% of surfactant (C_1%) presenting the smallest and most homogeneous particle size. A difference between the catalysts was also observed in the change of the crystalline phase after the reaction, where the C_1% catalyst presented the lowest loss of the Ni5Ga3 active phase. Methanol productivity showed positive relations with smaller particle size and higher quantity of Ni5Ga3 crystalline phase remaining after the reaction, with the C_1% catalyst presenting the highest methanol productivity. Catalytic evaluation under different conditions showed that higher temperature and GHSV values led to poorer selectivity to methanol. The C_1% catalyst also presented good activity at ambient pressure and remained stable after 5 h, with no deactivation. A mechanistic study employing DRIFTS analyses found that the reaction pathway on Ni-Ga alloy involved both the RWGS and formate routes, as shown by the presence of formate, methoxy, and CO intermediates.

Tri-reforming of methane (TRM) combines steam reforming, dry reforming, and partial oxidation of CH4 in a single reactor. The H2/CO product ratio usually ranges from 1.5 to 2.5, which makes the TRM...

Three Ni/CeZrO2/MgAl2O4 catalysts synthesized using different Zr/Ce molar ratios (0.25, 1, and 4) were studied for methane tri-reforming. The catalysts were characterized using XRD, 27Al-NMR, H2-TPR, CO2-TPD, XPS, and in situ techniques (XPD and XANES). The addition of CeZrO2 at Zr/Ce = 0.25 on the MgAl2O4 spinel support considerably reduced the amount of carbon deposits, because the methane decomposition reaction was attenuated by the presence of less agglomerated Ni0 species produced after the reduction process. The highest CO2 adsorption capacity (basicity) was associated with the participation of medium-strength basic sites, which facilitated coke gasification and led to higher CO2 conversions. A syngas with quality (H2/CO ratio) of 1.8 was produced, suitable for use in Fischer-Tropsch reactions.

In this study, we evaluated aspects of the CO2 hydrogenation mechanism, correlating structure-activity relationships of Cu-ZnO-ZrO2 catalysts prepared by one-pot surfactant-assisted co-precipitation with different surfactant ratios. Identifying the CO2 hydrogenation pathway intermediates is key to controlling the reaction selectivity. Experimental evidence shows that the CO2 is dissociating into CO* and O* onto the surface of the Cu-ZnO-ZrO2 catalyst. The adsorption and dissociation of CO2 were evidenced by a combination of in situ ambient-pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Fourier Transform Infrared Spectroscopy (FTIR) with a transmission cell. AP-XPS showed that the catalysts are composed of a Cu2+, Zr3+, and Zr4+ mixture and two kinds of Zn2+ species. After the H2 reduction process, only Cu2+ was reduced to Cu0. The Zn and Zr species were oxidized by the dissociated O* species. In situ transmission FTIR showed that CO was adsorbed onto the Cu+/0 sites. The catalyst with the higher surfactant molar ratio exhibited the highest CO2 conversion close to the equilibrium conversion, as well as a good methanol formation rate.

In this work, atomically dispersed rhodium over co-precipitated ceria-based supports were prepared by wet impregnation. The structural and surface properties of materials were investigated by X-ray diffraction, N2 physisorption isotherms, and X-ray photoelectron spectroscopy. The fraction of isolated sites was quantified by infrared spectroscopy using CO as a probe molecule. The formation of a defective surface by incorporation of 15% (mol/mol) of zirconium on ceria structure increased ~5-fold the fraction of isolated sites on catalyst compared to unmodified ceria. The doped-support efficiently trapped rhodium atoms avoiding agglomeration and increasing stability during CO oxidation reaction in a wide range of temperatures (30–200 °C) when compared to single-sites deposited on silica.

Supported Ni-Ga alloys have emerged as potential catalyst to mitigate CO2 emissions by its conversion into methanol at mild conditions, however, its performance depends on the optimization of the alloy-support effects, which is unclear up to now. Herein, we investigate the influence of alloy-support synergy in the catalytic performance of Ni5Ga3 supported on SiO2, CeO2, and ZrO2, by combining in-depth structural, chemical and spectroscopic characterization and density functional theory (DFT) calculations. In situ DRIFTS confirmed further hydrogenation of key reaction intermediates in Ni5Ga3/ZrO2 surface, while weak CO2 adsorption in Ni5Ga3/SiO2 avoided intermediate stabilization on the surface and, strong interaction with Ni5Ga3/CeO2 poisoned interface active sites. Additionally, the relative energies of reactants and key intermediates in the three distinct regions of the catalyst (support surface, alloy surface, and alloy-support interface), calculated through DFT, allowed us to propose a reaction mechanism for the most promising catalyst, Ni5Ga3/ZrO2.

Kinetic aspects of the operating parameters for the catalytic conversion of H2/CO2 to methanol over two novel catalysts were evaluated to understand the effect of the polymorphic ZrO2 phase composed of Cu0/+-ZnO sites at the atomic level and its impact on the reaction mechanism. The catalysts were characterized by in situ and ex-situ XRD, N2 adsorption/desorption isotherms, FRX, TPR, TPD-N2O, in situ XANES, TPD-CO2, and in situ DRIFTS techniques. The influence of different reaction variables such as the GHSV, temperature, pressure, and H2/CO2 ratio were studied using a fixed bed continuous plug flow reactor. The Cu-ZnO catalyst supported on the tetragonal zirconia polymorph exhibited the highest methanol yield due to the lower activation energy when compared to the catalyst with a greater amount of the monoclinic phase. In addition, the catalysts were reused for 8 cycles of 6 h to evaluate their stability, which can translate into lower costs for large-scale methanol production. The estimation of the kinetic parameters for the Cu-Zn oxide catalysts supported on ZrO2 polymorphs was important to understand the reaction mechanism, as well as to provide useful information for scaling up the process.

Value-added products synthesis by the one-step CO2 hydrogenation reaction has attracted much attention of researchers. In this paper, three catalysts: Cu/V-AlPILC,CuFe/V-AlPILC, and CuCo/V-Al PILC, prepared by impregnation method on Al-pillared clay support were studied. The effect of Fe and Co additives on the physicochemical properties of Cu-based catalysts was characterized by X-ray powder diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), N2 adsorption/desorption isotherms, temperature programmed reduction (TPR), Transmission Electron Microscope (TEM), X-ray photoelectron spectroscopy (XPS), N2O decomposition, CO2 and NH3 temperature-programmed desorption (CO2-TPD and NH3-TPD), and Fourier Transform Infrared Spectroscopy after gaseous pyridine adsorption (Py-FTIR) techniques. These catalysts were evaluated for CO2 hydrogenation into value-added products at temperatures ranging from 250 to 300 °C for 3 h and 40 bar pressure. Stability test was performed at 250 °C for 24 h and 40 bar pressure. The catalytic behavior revealed that a linear relationship does exist between the CO2 conversion with the metallic area. The DME and methanol synthesis showed a correlation with the basic and acid sites. The CuFe/V-Al PILC catalyst showed the highest selectivity for methanol and DME at 250 °C.

Hydrogen technology has been greatly increased in last decades as a promising solution to protect the environment. When carbon-based feedstocks are used, such as natural gas, biomass and biogas, the water gas shift reaction (WGSR) plays an important step in the production of high pure hydrogen for several purposes. By this reaction, the residual carbon monoxide in the gaseous stream (coming from steam reforming of carbon-based feedstocks) can be converted to carbon dioxide and then removed from the stream, avoiding the poisoning of industrial metallic catalysts as well as of electrocatalysts in fuel cells. Aiming to obtain no toxic catalysts that can replace the commercial chromium-doped hematite catalysts, lanthanum-doped hematite was studied in this work. Iron oxide-based samples with different amounts of lanthanum (La/Fe (molar) = 0.02; 0.08 and 0.2) were obtained by sol-gel method and calcined at 600. °C. The catalysts were characterized by X-ray diffraction, specific surface area measurements, temperature programmed reduction, Raman spectroscopy, Mössbauer spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. It was found that lanthanum affected the textural and reducing properties of hematite, depending on the amount. Moreover, lanthanum oxide increased the activity of hematite by decreasing the size of hematite crystals and then increasing the number of exposed active sites. In addition, lanthanum favored hematite reduction to produce magnetite (active phase). The activity increased with the amount of lanthanum in solids, the lanthanum-richest sample being the most active catalyst. Fil: Rangel, Maria do Carmo. Universidade Federal da Bahia; Brasil Fil: Querino, Peterson Santos. Universidade Federal da Bahia; Brasil Fil: Borges, Sarah Maria Santana. Universidade Federal da Bahia; Brasil Fil: Marchetti, Sergio Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas ; Argentina Fil: Assaf, José Mansur. Universidade Federal do São Carlos; Brasil Fil: Ruiz Vásquez, Doris Polett. Universidad de Concepción; Chile Fil: Rodella, Cristiane Barbieri. Centro Nacional de Pesquisa Em Energia E Materiais; Fil: Freitas Silva, Tatiana de. Universidade Federal do São Carlos; Brasil Fil: Marques da Silva, Alisson Henrique. Universidade Federal do São Carlos; Brasil Fil: Ramon, Adriana Paula. Universidade Federal do São Carlos; Brasil

Here, we have systematically investigated how the nature of the support influenced the oxygen mobility and activities in catalysts comprised of AgPt nanoshells deposited over inorganic oxides. We first synthesized AgPt nanoshells by galvanic replacement reaction between Ag nanospheres and PtCl6 2− (aq) combined with Pt reduction using hydroquinone as an auxiliary reducing agent. The nanoshells were then supported over TiO2, Al2O3 and CeO2. Through this methodology, we prepared materials with similar metallic nanoparticle AgPt compositions (~0.99 wt% Pt), sizes (43 ± 2 nm diameter), spherical shapes, surface morphologies, number of active sites $$ (\sim4.5\;\upmu{\text{mol}}\;{\text{g}}_{{{\text{cat}} .}}^{ - 1} ) $$ and uniform distribution over the supports, differing only in terms of the nature of the support. The oxide reduction temperature, its capability of re-oxidation and the presence of oxygen mobility were strongly dependent on the metal–support interaction between AgPt nanoshells and oxide supports. These properties have significantly influenced their catalytic performances toward the CO oxidation. At 230 °C, the CO oxidation TOF was 40.4 ± 0.4, 6.9 ± 1, 1.4 ± 0.8 min−1 for AgPt/CeO2, AgPt/TiO2, AgPt/Al2O3, respectively. These differences were attributed to the concentration of oxygen vacancies in each catalyst, which presented exactly the same trend as that of the catalytic activities. Our results may have important contributions to the design of highly active metal oxide-based catalysts toward gas-phase oxidation transformations.

The production of methanol (MeOH) and dimethyl ether (DME) through CO 2 hydrogenation is an attractive route to recycle CO 2 and control its emission to the atmosphere. In the present work, the hydrogenation of CO 2 into MeOH and DME over Al-pillared clays impregnated with different metals (Cu-X/V-AI PILC, where X = Ce and Nb) was investigated in the temperature range 200–300 °C. The influence of additives on the physico-chemical properties of the catalysts was evaluated by N 2 adsorption, ex situ XRD, TPR analysis, and in situ XANES and XRD. The acid sites were analyzed by FTIR analysis after adsorption of pyridine and NH 3 -TPD. The basic and metallic sites were analyzed by CO 2 -TPD and N 2 O-TPD, respectively. In situ XANES was used to investigate the Cu + and CuO species. MeOH and DME selectivities were directly related to the presence of acid, basic and metallic sites and with the reaction temperature. The results indicated that the CuCe/V-Al PILC catalyst was the most promising catalyst for DME synthesis from CO 2 .

One-pot synthesis of nanostructured ternary oxides of Ni, Al, and Ti was designed and performed via evaporation induced self-assembly (EISA). For the purpose of comparison, analogous oxides were also prepared by the impregnation method. The resulting materials were applied in two catalytic reactions: steam reforming of ethanol (SRE) for H2 production (subjected to prior activation with H2) and ethanol dehydration (ED; used without prior activation), to in situ analyze carbon accumulation by ethylene depletion when ethanol interacts with acidic sites present on the support. Modification of Ni–Al mixed oxides with titania was shown to have several benefits. CO2, NH3, and propylamine sorption data indicate a decrease in the strength of acidic and basic sites after addition of titania, which in turn slowed down the carbon accumulation during the ED reaction. These changes in interactions between ethanol and byproducts with the support led to different reaction pathways in SRE, indicating that the catalysts ob...

ABO 3 basic catalysts were synthesized by the nitrate-b-alanine solution combustion method at about 400 °C. The powders were formed by combustion route in times up to 5 min and presented high crystallinity and a single-phase, without the calcination step. XRD analyses showed that the oxides containing calcium (CaZrO 3 and Ca 0.9 Li 0.6 Zr 0.9 O 3 ) presented perovskite structure with the orthorhombic system, whereas a monoclinic structure was observed in the oxide Li 2 ZrO 3 . The catalysts were characterized by FEG-SEM, TPD-CO 2 , TGA, N 2 physisorption (BET) and ICP OES. The catalytic activity of the materials was tested in the transesterification of both methyl acetate (model reaction) and soybean oil with ethanol to produce biodiesel. Ca 0.9 Li 0.6 Zr 0.9 O 3 was the most active oxide in the model reaction, reaching a maximum conversion in ethyl acetate of 92%, followed by the oxide Li 2 ZrO 3 , with the conversion of 64%. The CaZrO 3 catalyst conversely presented negligible catalytic activity. Reuse tests have indicated that the catalysts containing Li can be reused for up to six reaction cycles, with an average conversion of around 50% up to its sixth reuse. Ca 0.9 Li 0.6 Zr 0.9 O 3 also shows promising for the biodiesel production since its FAEEs yield was good (60% m/m) under mild reaction conditions (molar ratio oil/ethanol 1:12 and 50 °C for 30 min). It was noticed that the incorporation of Li to calcium zirconate has resulted in more efficient and promising catalysts for the transesterification, what is possibly related to the textural and basic alterations occurred with the Li insertion. Although the metallic ions leaching of the most active materials has been detected, no reaction was observed in homogeneous phase.

Among the several classes of chemical reactions, the green oxidation of organic compounds has emerged as an important topic in nanocatalysis. Nonetheless, examples of truly green oxidations remain scarce due to the low activity and selectivity of reported catalysts. In this paper, we present an approach based on the optimization of both the support material and the active phase to achieve superior catalytic performances towards green oxidations. Specifically, our catalysts consisted of ultrasmall Au NPs deposited onto MnO2 nanoflowers. They displayed hierarchical morphology, large specific surface areas, ultrasmall and uniform Au NPs sizes, no agglomeration, strong metal-support interactions, oxygen vacancies, and Auδ+ species at their surface. These features led to improved performances towards the green oxidations of CO, benzene, toluene, o-xylene, glucose, and fructose relative to the pristine MnO2 nanoflowers, commercial MnO2 decorated with Au NPs, and other reported catalysts. We believe that the catalytic activities, stabilities, and mild/green reaction conditions described herein for both gas and liquid phase oxidations due to the optimization of both the support and active phase may inspire the development of novel catalytic systems for a wealth of sustainable transformations.

The preferential oxidation of CO (CO-PROX) is promoted at the interface between CuO and CeO

The innumerous advantages of heterogeneous catalysts employed in biodiesel production have stimulated the search for a solid catalyst capable of replacing the industrially used homogeneous catalysts. This paper investigates the effect of the sol-gel method in the catalytic activity and stability of Li-MgAl mixed oxides prepared by the “in situ” lithium addition to a MgAl hydrotalcite. The analyses based on N2 physisorption, thermogravimetric analysis, X-ray diffractometry, scanning electron microscopy and temperature-programmed desorption of CO2 were carried out to elucidate the properties of the catalysts. Considerable differences in the physico-chemical properties of the catalysts were observed with the Li addition. Li reduced the surface area and increased the crystallite size of the oxides. Furthermore, Li-MgAl mixed oxides prepared by the calcination of the sol-gel MgAl hydrotalcites presented substantial morphological differences when compared to the same oxides obtained by heat treatment of hydrotalcites synthesized via the conventional co-precipitation route. Furthermore, Li increased the number and strength of the base sites which resulted in the increase of the oxide reactivities towards the transesterification reaction between methyl acetate and ethanol. The activity was dependent on the Li loading on the catalysts. The catalyst containing only 5 wt.% Li turned out to be highly active (( 85% conversion at 50°C, ethanol/methyl acetate molar ratio = 6/1, 4 wt.% of catalyst and 30 min of reaction). Stability tests showed that the Li-MgAl catalysts lose activity after 3 reuse cycles.

Mixed oxide catalysts derived from hydrotalcites were applied to model biogas reforming (CH 4 :CO 4 = 1.5:1). Ni x /MgAl and Ni x /MgAlCe (x = 10% or 25% w/w nominal nickel content) were prepared by the coprecipitation method. Both Ni10%/MgAl and Ni10%/MgAlCe catalysts showed potential for syngas production due to their stability. CO 2 -TPD measurements and XANES results helped understand the Ni10%/MgAl and Ni10%/MgAlCe catalysts performance be similar. XANES spectra suggested that the majority of Ni +2 would be present inside the solid solution in Ni10%/MgAlCe, making the activation process more difficult, which probably compromised the conversions enhancement in relation to Ni10%/MgAl. The H 2 /CO ratio lower than unity makes the obtained syngas suitable for the Fischer-Tropsch process. The carbon deposits on Ni10%/MgAlCe catalyst were less stable, which means that it could be gasified more easily.

Catalysts based on CaO/MgAl oxides were prepared by Ca(NO 3 ) 2 .4H 2 O impregnation onto MgAl hydrotalcite followed by calcination at 600 °C/0.5 h. The materials were characterized by means of XRD, N 2 physisorption, FEG-SEM equipped with energy-dispersive X-ray spectroscopy (EDS) and TPD of CO 2 . The oxide reactivities were evaluated using the model transesterification reaction between methyl acetate and ethanol under mild reaction conditions (50 °C, ethanol/methyl acetate molar ratio = 6/1 and 4 wt.% of catalyst). MgAl mixed oxide was inactive for transesterification. On the other hand, the Ca addition onto the oxides considerably increased the base site amounts and strengths of the Ca/MgAl, greatly improving their catalytic performances. Remarkably high conversions were obtained for 40-Ca/MgAl compared to commercial CaO. Thus, the CaO dispersion over MgAl mixed oxide showed to significantly improve the catalytic performance of CaO. Stability tests revealed that the Ca/MgAl can be reused for at least 5 reaction cycles and the reaction occurs through a heterogeneous process. Due to the high activity, this type of catalyst can be pointed as a promising heterogeneous catalyst for biodiesel production although the Ca leaching must be formerly resolved for practical use.

Ni catalysts supported on calcined Mg–Al hydrotalcite, Mg(Al)O, were prepared and the effect of the addition of La and/or Rh was tested in the performance of the catalysts in the dry reforming of methane with excess of methane in the feed, simulating a model sulfur-free biogas. The effect of adding synthetic air was assessed. The catalysts were characterized by surface area (BET), XRD, TPR and XPD. The results showed the reconstruction of the hydrotalcite structure during the Ni(NO3) impregnation, with the segregation of the lanthanum. In the catalyst without Rh and La, Ni showed a strong interaction with the support Mg(Al)O, showing high reduction temperatures in TPR test. The addition of Rh and La increased the amount of reducible Ni species and facilitated the reduction of the species interacting strongly with the support which resulted in high rates of carbon deposition. The NiMgAl catalyst presented the strong Ni-support interactions and the best performance with low carbon deposition at both conditions of reaction. The NiMgAl catalyst did not present deactivation during 24 h of stability testing in the oxidative reforming of a model biogas.

SURFACES+NSP; Environmental problems related to the use of fossil fuels and the development of new technologies for energy production from hydrogen have renewed the interest for the water gas shift reaction (WGSR). For several years, the WGSR has been used to eliminate carbon monoxide from hydrogen-rich streams produced during natural gas reforming, as well as to increase hydrogen production. For reasons of economy, in industrial processes the reaction is carried out in two steps at different temperatures. There is, however, interest to develop catalysts able to operate at one step at intermediate temperatures. In a previous work, we had found that nickel-based catalysts prepared from hydrotalcite-like precursors were promising for WGSR in a single step. In the present work, the influence of the nickel amount on the properties of the catalysts was investigated, in order to find the best formulation for these catalysts. The samples were prepared by precipitation techniques and characterized by chemical analysis, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, specific surface area and porosity measurements, temperature programmed reduction, X-ray photoelectron spectroscopy and transmission electron microscopy. The catalysts were evaluated in WGSR at 1 atm and at different temperatures. During the heating of hydrotalcite-like precursors, aluminum cations were incorporated into the nickel oxide lattice, hindering the reduction of this oxide; however, the addition of zinc decreased this effect. The existing interaction between nickel oxide and alumina (gamma-Al2O3) is comforted by the observation of Moire fringes caused by the interference of crystallographic planes of both phases. All catalysts were active in the WGSR but the nickel-richest ones also produced methane, this effect being diminished or prevented by the addition of zinc to the catalysts. No simple relationship was found between nickel amount and the activity or selectivity of the catalysts probably due to the different interactions among the metals at different reaction temperatures. The most efficient catalyst was obtained by heating the N(0.37)Z(0 37)A(0.25) hydrotalcite, which produces a solid able to work in WGSR in one step at an intermediate temperature (300 degrees C) leading to 100% of carbon monoxide conversion without producing methane. Copyright (c) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

A mesoporous zirconia (ZrO2) series was synthesized by reflux and hydrothermal methods using Pluronic (P-123) as a surfactant. Characterizations by XPD showed that the ZrO2 prepared via reflux consisted of only tetragonal crystalline phase when compared with that obtained by hydrothermal treatment, which was formed by tetragonal and monoclinic phases. The addition of the surfactant had a positive influence on the specific surface area and mesoporous structure ordering of ZrO2, regardless of the method of synthesis. The surface interaction of H2/CO2 mixture with the ZrO2 samples exhibited some dissimilarity due to the unlike surface acidic-basic features of the tetragonal and monoclinic phases. In-situ DRIFTS experiments revealed that the species adsorbed on the zirconia prepared by the reflux method were bidentate bicarbonate, ionic bicarbonate, bidentate carbonate, and polydentate carbonate, whereas the adsorption on the zirconia prepared by refluxing method led to increased intensity of the broadband characteristic of bidentate carbonate and the appearance of two new bands typical of bidentate carbonate and bidentate bicarbonate. After subsequent switching off CO2, it was observed that the carbonate species (1550 cm−1) strongly interacted with the zirconia surface and required high energy amount to be desorbed, which was in good agreement with the CO2-TPD profile. This suggests that these carbonates are not active species when the reaction is carried out at 200 °C.