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The preparation and stabilization of gold nanoparticles with a precise control of size and dispersion is highly attractive for a variety of applications, and a key aspect is thermal stability of the nanoparticles. This paper focuses on understanding the effect of TiO2-based nanodomains, dispersed on mesoporous silicas, and how they control gold nanoparticle stability. The anatase domains have been incorporated through two different strategies: co-hydrolysis of Si and Ti reagents that directly form the mesoporous material through self-assembling with surfactant micelles, or the post-impregnation of the mesosporous silica with Ti(acac)2. Both strategies lead to different incorporation of the anatase domains: partially embedded inside the silica walls, or occupying the mesopores. We have observed that the inclusion in the pores favors the stability of the final material due to a more favorable gold-support interaction and also due to a stabilizing effect associated with a scaffold effect of the anatase crystals, which hinders the collapse of the mesostructure.

The catalytic upgrading of crude bio-oils obtained through the pyrolysis of lignocellulosic biomass remarkably improves the properties of the final bio-oil. It has been demonstrated that the impregnation of hierarchically structured ZSM-5 zeolites with metal cations (Sn, Cu, Ni or Mg) promotes oxygen removal. Remarkably, the Mg-loaded hierarchical zeolite has led to the best fuel characteristics, achieving the greatest reduction in the oxygen-content and the lowest acidity. The promotion of ketonization reactions of acids with aldehydes to produce ketones seems to be favored over the Lewis acid sites created after incorporation of Mg cations at the ion exchange sites. A slightly lower deoxygenation rate is obtained for Cu-loaded hierarchical ZSM-5 zeolite. However, some subtle differences are identified. The most significant feature is the remarkable amount of evolved CO observed in the gas fraction. Thus, it could be assumed that decarbonylation of acids to aldehydes at Cu cations incorporated at ion exchange positions seems to be the prevalent deoxygenation reaction for this solid. Similarly, the preferential mechanism for O-removal using hierarchically structured Ni and Sn-ZSM-5 zeolites derived catalysts seems to proceed through decarbonylation and decarboxylation reactions at the metal acid Lewis sites. Although a prevalent reaction mechanism could not be identified, lower cation incorporation at ion exchange positions could explain the inferior deoxygenation rate. In all the cation-loaded hierarchical zeolites, the incorporation of metallic species at the ion exchange sites decreases the production of desired aromatics and this is linked with a lower amount of Brønsted acid sites.

One-pot combination of the in-situ generation of hydrogen peroxide (H2O2) with selective oxidation reactions enhances the environmental and economic attractiveness of the use of H2O2 as green oxidant at industrial scale. This tandem reaction improves not only the safety aspects associated to H2O2 storage and transportation but also reduces the capital and operation costs. This review covers the progress in the field focussing on the areas of catalysis development, mechanistic understanding and engineering approaches (such as membrane reactors) for specific systems involving epoxidation of propylene oxide, hydroxylation of benzene, oxygenate synthesis from methane and Fenton processes, highlighting the main challenges to overcome in the near future.

Air pollution poses a major environmental concern worldwide. In metropolitan areas, motor vehicle exhaust contributes a major source of contaminants. More restrictive legislations regarding automotive emissions resulting in a remarkable decrease in the amount of pollutants associated to new vehicles. With current three-way catalysts (TWC), a recognized challenge in preventing these emissions is the lack of treatment capacity of hydrocarbons (HC) and CO under cold-start conditions. Fresh catalysts start to operate at ca.170 ºC, but aged catalysts light-off at ca. 200-225 ºC. These catalysts need between 60 to 120 seconds to reach these temperatures and during this time, about 50 to 80% of unburned HCs and around 80% CO are emitted. To curb the HC emissions, the incorporation of an inorganic nanoporous material to act as a HC trap prior to the TWC, is one of the most promising solutions. Zeolites are often considered as HC trap materials due to their stability under a variety of conditions. Different zeolites and zeotypes, with varying pore dimensionality and pore network connectivity, have been studied as adsorbents for HC emission control during the cold-start period. However, none of the reported materials have demonstrated the necessary characteristics of a HC trap under very demanding operational conditions. In this sense, a priority goal is to find an adsorbent that fulfills this requirement.

A set of catalysts comprised of gold on different CeO2 supports has been prepared by a nanocasting route and characterized by several physicochemical techniques. These catalysts have been tested for CO oxidation and show outstanding catalytic activity. Higher calcination temperatures of the hard template, producing a poorly ordered silica template, have led to a higher amount of oxygen vacancies on the surface of CeO2. The presence of surface oxygen defects in the support combined with the deposition of Au nanoparticles (ca. 3 nm) homogeneously dispersed on the CeO2 support may explain the excellent behaviour for low temperature CO oxidation. Surprisingly, it has been observed that the degree of inverse replication of the template is not relevant in the catalytic performance, as in all cases neither the characteristics of the ceria surface nor the dispersion and oxidation state of gold are greatly modified by the formation of inter-particle bridges.

The development of rapid and accurate techniques to predict the composition of crude bio-oils obtained via the pyrolysis of lignocellulosic biomass is a prerequisite for their industrial implementation. Here, we demonstrate the potential of the Fourier Transform Infrared Spectroscopy to replace the gas chromatography-mass spectrometry (GC-MS) in determining the compositional groups of bio-oils. Using mid-infrared spectroscopic technique as predictor, chemometric tools based on partial least squares regression models were contrasted with GC-MS results to foresee the various families of organic compounds. A broad data set, consisting of more than one hundred samples obtained from the thermal and catalytic pyrolysis of woody biomass and from the upgrading of bio-oil vapors by catalytic cracking over zeolites and metal oxides was used. The applicability of the developed model was assessed by external validation using the Kennard-Stone algorithm, showing that more than 90 wt% of the bio-oil composition was accurately determined. These results pave the path for the on-line monitoring of the forthcoming manufacture system of second-generation biofuels through rapid and costeffective characterization of the pyrolysis bio-oils, thus enabling industrial producers to make timely decisions.

A highly effective hydrocarbon (HC) trap for the abatement of cold start HC emissions with specific adsorption sites for the different molecules present in the exhaust gases has been designed by means of molecular simulation tools, and later synthesized.

The modelling of breakthrough curves obtained in the adsorption of propene as a model compound onto different inorganic solids is described. All the runs were performed in a fixed bed at atmospheric pressure, employing a process temperature of 30 °C and propene concentrations in the range 0.0022–0.0222 mol/Nm3. The experimental conditions were therefore similar to those observed in the initial flue gases of cold start engines. The work described was mainly focused on the study of the influence of the adsorbent characteristics (composition, porous structure and surface area) on the kinetics of the adsorption process. The equilibrium adsorption values were initially determined from the breakthrough curves and satisfactorily fitted by the Langmuir isotherm model. These values were then used together with experimental breakthrough curves to analyse the kinetic expressions obtained applying the Linear Driving Force (LDF) model to the dynamic adsorption process. Values of the mass-transfer coefficient, surface and effective diffusion coefficients of propene have been calculated and are reported.

A key target to reduce current hydrocarbon emissions from vehicular exhaust is to improve their abatement under cold-start conditions. Herein, we demonstrate the potential of factorial analysis to design a highly efficient catalytic trap. The impact of the synthesis conditions on the preparation of copper-loaded ZSM-5 is clearly revealed by XRD, N2 sorption, FTIR, NH3-TPD, SEM and TEM. A high concentration of copper nitrate precursor in the synthesis improves the removal of hydrocarbons, providing both strong adsorption sites for hydrocarbon retention at low temperature and copper oxide nanoparticles for full hydrocarbon catalytic combustion at high temperature. The use of copper acetate precursor leads to a more homogeneous dispersion of copper oxide nanoparticles also providing enough catalytic sites for the total oxidation of hydrocarbons released from the adsorption sites, although lower copper loadings are achieved. Thus, synthesis conditions leading to high copper loadings jointly with highly dispersed copper oxide nanoparticles would result in an exceptional catalytic trap able to reach superior hydrocarbon abatement under highly demanding operational conditions.

A key target to reduce current hydrocarbon emissions from vehicular exhaust is to improve their abatement under coldstart conditions. Here, we demonstrate the exceptional properties of a hierarchical Cu/HZSM5 zeolitebased system as a catalytic trap. The largely increased external surface area coupled with the preserved intrinsic properties attainable upon alkaline treatment and subsequent acid washing of a conventional ZSM5 zeolite enable an improved dispersion of copper species in the hierarchical counterpart. The impact of postsynthetic modification on the preparation of coppercontaining ZSM5 is clearly revealed by XRD, N2 sorption, FTIR, NH3TPD, TEM, SEM, and HAADFSTEM. By providing stronger adsorption sites, the introduction of copper species improves the retention of propene and toluene with respect to the protonic zeolites, and enables their further conversion to carbon dioxide and water on reaching its desorption temperature. The equivalent adsorption capacity and improved oxidation activity and lower susceptibility to deactivation exhibited by the hierarchical Cu/HZSM5 catalyst visavis its conventional counterpart yield a superior bifunctional catalyst able of reach full hydrocarbon conversion under realistic operating conditions.

A key target to reduce current hydrocarbon emissions from vehicular exhaust is to improve their abatement under cold-start conditions. Herein, we demonstrate the potential of factorial analysis to design a highly efficient catalytic trap. The impact of the synthesis conditions on the preparation of copper-loaded ZSM-5 is clearly revealed by XRD, N2 sorption, FTIR, NH3-TPD, SEM and TEM. A high concentration of copper nitrate precursor in the synthesis improves the removal of hydrocarbons, providing both strong adsorption sites for hydrocarbon retention at low temperature and copper oxide nanoparticles for full hydrocarbon catalytic combustion at high temperature. The use of copper acetate precursor leads to a more homogeneous dispersion of copper oxide nanoparticles also providing enough catalytic sites for the total oxidation of hydrocarbons released from the adsorption sites, although lower copper loadings are achieved. Thus, synthesis conditions leading to high copper loadings jointly with highly dispersed copper oxide nanoparticles would result in an exceptional catalytic trap able to reach superior hydrocarbon abatement under highly demanding operational conditions.

A high percentage of hydrocarbon (HC) emissions from gasoline vehicles occur during the cold-start period. Among the alternatives proposed to reduce these HC emissions, the use of zeolites before the three-way catalyst (TWC) is thought to be very effective. Zeolites are the preferred adsorbents for this application; however, to avoid high pressure drops, supported zeolites are needed. In this work, two coating methods (dip-coating and in situ crystallization) are optimized to prepare BETA zeolite thin films supported on honeycomb monoliths with tunable properties. The important effect of the density of the thin film in the final performance as a HC trap is demonstrated. A highly effective HC trap is prepared showing 100 % toluene retention, accomplishing the desired performance as a HC trap, desorbing propene at temperatures close to 300 °C, and remaining stable after cycling. The use of this material before the TWC is very promising, and works towards achieving the sustainability and environmental protection goals.

Cold start tests are carried out to evaluate the performance of copper-exchanged zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the role of copper in the performance of these zeolites. It is concluded that the partial substitution of the protons in the parent H-ZSM-5 zeolite is highly beneficial for hydrocarbon trapping due to the formation of selective adsorption sites with specific affinity for the different exhaust components. However, it is also observed that uncontrolled exchanging process conditions could lead to the presence of CuO nanoparticles in the zeolite surface, which seem to block the pore structure of the zeolite, decreasing the hydrocarbon trap efficiency. Among all the zeolites studied, the results point out that a CuH-ZSM-5 with a partial substitution of extra-framework protons by copper cations and without any detectable surface CuO nanoparticles is the zeolite that showed the best performance under simulated cold start conditions due to both the high stability and the hydrocarbon retaining capacity of this sample during the consecutive cycles.

Simulated cold-start tests have been carried out to evaluate the performance of H-ZSM-5 and H-BETA zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the effect of water on their behaviour. It is concluded that the hydrothermal treatment of the zeolites in the acidic form contributes to the better performance of these materials as hydrocarbon traps since the stabilization of the zeolites takes place. Moreover, the decrease of the surface acidity of the zeolites results in an increase of the Si/Al ratio, which contributes to the decrease of the water affinity for adsorption sites. Thus, the competition with hydrocarbon molecules in the exhaust for the adsorption sites is reduced which increases their trap efficiency. The stabilized H-ZSM-5 is the zeolite that showed the best performance with a propene offset temperature of 240 °C, which should be high enough for the three-way catalyst to carry out its role as catalytic converter.

Cold start tests are carried out to evaluate the performance of copper-exchanged zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the role of copper in the performance of these zeolites. It is concluded that the partial substitution of the protons in the parent H-ZSM-5 zeolite is highly beneficial for hydrocarbon trapping due to the formation of selective adsorption sites with specific affinity for the different exhaust components. However, it is also observed that uncontrolled exchanging process conditions could lead to the presence of CuO nanoparticles in the zeolite surface, which seem to block the pore structure of the zeolite, decreasing the hydrocarbon trap efficiency. Among all the zeolites studied, the results point out that a CuH-ZSM-5 with a partial substitution of extra-framework protons by copper cations and without any detectable surface CuO nanoparticles is the zeolite that showed the best performance under simulated cold start conditions due to both the high stability and the hydrocarbon retaining capacity of this sample during the consecutive cycles.

Simulated cold-start tests have been carried out to evaluate the performance of H-ZSM-5 and H-BETA zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the effect of water on their behaviour. It is concluded that the hydrothermal treatment of the zeolites in the acidic form contributes to the better performance of these materials as hydrocarbon traps since the stabilization of the zeolites takes place. Moreover, the decrease of the surface acidity of the zeolites results in an increase of the Si/Al ratio, which contributes to the decrease of the water affinity for adsorption sites. Thus, the competition with hydrocarbon molecules in the exhaust for the adsorption sites is reduced which increases their trap efficiency. The stabilized H-ZSM-5 is the zeolite that showed the best performance with a propene offset temperature of 240 °C, which should be high enough for the three-way catalyst to carry out its role as catalytic converter.

A morphological phase diagram is determined to relate the effect of base concentration and temperature during the hydrothermal synthesis with the final ceria nanostructured morphology. Representative samples of nanoparticles, nanorods and nanocubes have been characterized by XRD, N2 adsorption, TEM, XPS and Raman and catalytically tested for the total oxidation of naphthalene as a model polycyclic aromatic hydrocarbon. Ceria nanoparticles present the highest surface area and smallest crystalline size, leading to the most active of these structures. However if the catalytic activity is normalized by unit of surface area, the observed reactivity trend (nanorods

A theoretical model was built to simulate the adsorption–desorption process of propane onto a Na-ZSM-5 zeolite in a fixed bed under cold start conditions. This model was validated on a set of experimental data obtained for the adsorption, desorption and cold start cycles. The influence of operation conditions was modelled with various propane contents at the inlet of the adsorber, several heating rates in the furnace and space velocities ranging from 2000 to 5500 h−1. Breakthrough curves, desorption cycles and cold start cycles were computed with a coefficient of determination of 0.98, 0.88 and 0.81, respectively. From the comparison of simulated and experimental results, it is evident the high versatility of the model as well as the high accuracy grade.

La presente invención se refiere a una trampa catalítica de hidrocarburos contenidos en gases de escape producidos por un motor de combustión interna, caracterizada porque está libre de metales nobles y comprende al menos una capa de un tamiz molecular de fórmula XH-ZSM-5, donde X representa uno o varios metales de transición y H-ZSM-5 representa una zeolita con una relación Si/Al comprendida entre 10 y 20, que presenta en su estructura interior un intercambio iónico de protones por cationes metálicos en un porcentaje comprendido entre el 20% y el 60% del total de protones presentes en la zeolita en su estado original. La invención también contempla el método de obtención de dicha trampa, su uso en un convertidor catalítico de un motor de combustión y en el propio motor, así como el método de eliminación de hidrocarburos mediante dicha trampa.

During the last twenty years the number of patent publications in the field of the control of hydrocarbon compounds during the cold start period of a gasoline engine has strongly increased and seems now that the number of patents tends to increase during the following years. This fact has been related with increasingly stringent legislations all over the world which highlights the importance of developing efficient systems for the control of cold start hydrocarbon emissions. The technologies that show a higher number of patents are the hydrocarbon trap, the close-coupled catalyst and the electrically heated catalyst.

The lack of treatment capacity of hydrocarbons by three-way catalysts during the “cold start” period creates an important environmental problem. During this period, the temperature of the three-way catalyst is too low for effective operation and cannot convert the hydrocarbons in the exhaust. 50–80% of the total hydrocarbon emissions are produced in this phase that accomplishes the first 60–120 s of the engine operation. In this study, the technology chosen to treat these emissions is the use of HC-traps, and molecular simulations are tested as a tool to reproduce the experimental adsorption behaviour of porous solids. Therefore, experimental and simulated adsorption isotherms of propene (model hydrocarbon) have been obtained for four different crystalline materials with distinctive framework structures (3D and 1D) and a variety of Si/Al ratios and cations (three zeolites: ZSM-5, BETA and Mordenite; and a silicoaluminophosphate molecular sieve: SAPO-5).

Cerium oxides have been prepared by nanocasting of a mesoporous siliceous KIT-6. Through this synthesis method a partially ordered mesoporous structure, as demonstrated by several characterization techniques (N2 adsorption, XRD and HRTEM) has been obtained. Accordingly, very high surface areas have been achieved (up to 163 m2/g), despite using high calcination temperatures (550 °C). We have demonstrated that the aging temperature of the siliceous template is of outstanding importance, as this parameter is directly responsible for both the pore size and the surface area of the catalysts. In addition, whilst a low preparation temperature (40 °C) makes the further removal of the silica template difficult, higher temperatures lead to more compact frameworks with a higher interconnectivity among the networks. These cerium oxide materials have been tested as catalysts for the total oxidation of naphthalene, and display excellent activity, remarkably higher than commercial CeO2. The mesoporous ceria catalysts also demonstrate a high degree of stability with extended time-on-stream and most importantly using high reaction temperatures.

Ceria catalysts have been prepared by a nanocasting procedure using SBA-15, MCM-48 and KIT-6 silica-based templates, and investigated for the total oxidation of naphthalene. In all cases cubic fluorite CeO2 was prepared, and the structure of the template was replicated when SBA-15 and MCM-48 were used. The KIT-6 template was not replicated by the nanocasting synthesis, but in all cases mesoporous CeO2 was obtained with high surface areas (91–190 m2 g−1). All of the catalysts demonstrated high activity for naphthalene oxidation to CO2, and the most active was the catalyst prepared from the KIT-6 template. The high activity was attributed to the small crystallite size of the CeO2, combined with high surface area and the highly accessible catalyst surface.