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The hydrogenation of CO2 into methane is considered a plausible process to storage renewable energy in form of methane and reducing CO2 anthropogenic emissions. Microporous solids such as zeolites have been scarcely studied yet for this application. This study aims to evaluate and compare the catalytic performance of zeolite (Y and BETA) supported Ni catalysts for CO2 methanation. The physicochemical properties of the prepared catalysts were characterized by XRD, BET, CO2-TPD, H2-TPR and XPS, and CO2 methanation was carried out in a tubular reactor at conditions of H2/CO2 = 4, GHSV = 10,000 h−1 and temperatures from 200 to 500 ⁰C. Neutralization of both zeolites by Na+ ion exchange enhanced the CO2 conversion as weaker CO2 adsorption sites and reducibility are promoted. BETA resulted in a better support than Y zeolite due to the presence of more easily reducible Ni2+, which acts as precursor of active Ni° accessible under reaction conditions. Indeed, the surface basicity and Ni dispersion of Ni/BETA catalysts were considerably promoted by impregnation of different loads of La2O3, which increase the amount of CO2 adsorption sites and even active hydrogenation sites resulting in a significant increase of activity and selectivity towards CH4. The optimal Ni-10%La2O3/Na-BETA formulation resulted in T50 of 320°C, CO2 conversion of 65% at 350 °C, with almost total selectivity to CH4 and maintaining stability for more than 24 h.

Conventional Ni/Al2O3 catalyst, currently used for COx removal in ammonia production, admits room for improvement as catalysts for application in low temperature CO2 methanation, which is the aim of this work. The Incipient Wetness Impregnation (IWI) has been replaced by Glycerol Assisted Impregnation (GAI) method and, afterwards, a secondary metal (Ru) has been co-impregnated forming a bimetallic system. The monometallic as well as bimetallic systems have been characterized by several techniques (TGA, XRD, N2-physisorption, TEM, H2-TPR, H2-TPD, STEM-EDX and operando FTIR) and tested for CO2 methanation reaction in a downflow fixed bed reactor (conditions: P =1 bar, H2: CO2 ratio = 4 and WHSV = 30,000 mL h−1 g−1). GAI method together with a reducing calcination atmosphere (20 %H2/N2) results effective to avoid the formation of large metal particles during the synthesis, especially for Ru/Al2O3 formulation. In fact, the Ru dispersion of the catalyst prepared by GAI (RuAlGAI) is around 5 times higher than that of RuAlIWI catalyst. On the other hand, NiAlGAI presents larger population of reduced particles but bigger in size than NiAlIWI catalyst, which finally provides the former with slightly higher metal surface and superior catalytic performance. By co-impregnating small amounts of Ru (0.5, 1.0 or 1.5 wt%) the Ni surface is considerably increased which, together with Ru synergistic collaboration, results in a methane yield rise from 20 to 44 % at 300 °C. The operando FTIR results show no differences in the reaction pathway with GAI preparation method and incorporation of Ru, but different evolution of reaction intermediates concentration with temperature. The bimetallic Ni-RuAl system presents much higher capacity to adsorb CO and hydrogenate the reaction intermediates (adsorbed formates and carbonyls) by dissociated H2 than its monometallic counterparts.

A series of VOx/TiO2/ZSM5 were prepared in order to enhance the acid functionalities of commercially used VOx/TiO2 for the combined abatement of NO and o-dichlorobenzene (o-DCB, model molecule to simulate dioxins and furans) from the off-gases of a Municipal Solid Waste (MSW) incinerator plant. The catalysts have been prepared by wet impregnation varying the TiO2 content from 0 to 46%. VOx/TiO2 was also prepared as a reference sample. Combining catalysts characterization (N2 adsorption-desorption isotherms, XRD, TEM, NH3-TPD, H2-TPR and Raman) and activity data, we found that high TiO2 loading VOx/TiO2/ZSM5 catalyst, is highly suitable catalyst for dDiNOx process. The NO conversion is higher than the reference VOx/TiO2 catalyst partly due to higher amount of acid sites provided by the zeolite and partly due to Ti-V interaction, which is a key factor in the conversion of both o-DCB and NO. The TiO2 is heterogeneously dispersed over zeolite, but VOx dispersion is enhanced as the TiO2 content is increased, leading to a higher active polymeric species contribution, as in the sample V/46Ti/Z (confirmed by correlation between TOF and Ti-V interaction).

A series of metal loaded ZSM5 including Cu/, Fe/, Mn/ and V/ was prepared and their catalytic activity, selectivity and durability were compared with the commercially used VO x /TiO 2 catalyst for the combined abatement of NO and o -dichlorobenzene ( o -DCB, model molecule to simulate PCDD/Fs) from the off-gases of a municipal waste incinerator (MWI) plant. Catalysts textural, acid and redox properties have been characterized by N 2 adsorption–desorption isotherms, XRD, NH 3 -TPD and H 2 -TPR and a higher surface area, acidity and reducibility of the metal loaded zeolite catalysts have been confirmed. By catalytic tests carried out in the experimental conditions close to those employed in MWI plants, it was concluded that VO x /TiO 2 show higher catalytic performance than metal/zeolite catalysts. A relationship between metal reducibility and the catalyst activity was found. However, zeolites due to their high acidity are less selective to NH 3 oxidation reaction (negligible N 2 O formation) and therefore higher NO conversion is obtained in a wider operating temperature window. Using zeolites selectivity to CO is lower, although traces of trichlorobenze are detected. Both reactions are well fit to first order reaction kinetic over all the catalysts. In addition, neither of the catalysts show evidence of deactivation during 12 h of reaction. Among metal/zeolites, Cu/Z is the most active catalyst, whereas Fe/Z is the less for both NO reduction and o -DCB oxidation reactions. Unfortunately, Cu/Z high selectivity to highly chlorinated compounds, like trichlorobenzene, was also found.

Fe-ZSM-5 zeolite was synthesized by following different routes namely ion exchange from solution, impregnation and solid state ion exchange. All the catalysts were tested in the oxidation of trichloroethylene (TCE) in vapor phase. The catalysts were characterized using different physico-chemical technique which included BET surface area analysis, NH3-TPD analysis, H2-TPR analysis, XRD analysis, TEM analysis, DRS UV–vis, EPR, and XPS. The characterization results gave significant insight on the active sites responsible for the oxidation. It was found that Fe nanoparticles present in the extra framework of the zeolite were largely responsible for oxidation rather than the acidic sites. The catalysts prepared by impregnation or solid state ion exchange method were found to be active in the oxidation of TCE; however, comprehensively less active than the catalyst synthesized by ion exchange method. The activity of Fe-ZSM-5 was also compared with H-ZSM-5, and it was found that the activity and stability of Fe-ZSM-5 catalyst was much higher than the protonic form. Studies on the deactivation mechanism of the catalysts showed that the major reason for loss in activity was due to formation of FeCl3 rather than coke deposition.

The use of fossil fuels to satisfy the growing energy demand results in the emission of a huge amount of CO2 to the atmosphere. One alternative to overcome this environmental issue is the CO2 valorization through the storage and in situ hydrogenation to CH4. In this work, Ru-CaO/Al2O3 and Ru-Na2CO3/Al2O3 dual function materials are synthesized with different adsorbent loadings, namely 5, 10 and 15 wt.%. The prepared catalysts are characterized in terms of surface area by N2 adsorption and desorption, crystallinity by XRD, Ru dispersion by H2-chemisorption and TEM, basicity by CO2-TPD and reducibility and oxidation state of the noble metal by H2-TPR and XPS. Temperature programmed surface reaction experiments with H2 on samples with pre-adsorbed CO2 reveal that the decomposition of surface carbonates and the subsequent hydrogenation occurs at lower temperatures for catalysts containing Na2CO3 than CaO. A complete reaction scheme describing the CO2 adsorption and hydrogenation process has been proposed based on the temporal evolution of reactants and products. Oxides (CaO or Na2O) and hydrated oxides (Ca(OH)2 or NaOH) have been identified as CO2 storage sites, the former oxides being more reactive towards the CO2 adsorption. CH4, H2O and minor amounts of CO are detected during the hydrogenation step. The CO2 storage and hydrogenation to CH4 is promoted with increasing the adsorbent loading. Maximum CH4 production of 414 μmol g−1 is observed for Ru15%CaO/Al2O3 at 400 °C. High temperature is needed to efficiently decompose the highly stable carbonates formed onto CaO. On the other hand, the higher Ru dispersion along with a lower stability of carbonates in Ru10%Na2CO3/Al2O3 promotes CH4 formation (383 μmol g−1) at notably lower temperature, i.e. 310 °C. Thus, Ru10%Na2CO3/Al2O3 is regarded as a suitable catalyst for the CO2 storage and in situ hydrogenation to CH4.

The activity of three-way catalysts is highly dependent on the reactants present in the automobile exhaust gases (CO, NO x , HC, O 2 , H 2 O, CO 2 , N 2 ) as well as their relative concentration. Thus, the influence of each reactant on the kinetic behavior of the whole mixture makes difficult to establish the accurate kinetics of the system. Activity experiments carried out close to the real operation conditions (GHSV, concentration, etc.) with a Pt/CeO 2 /Al 2 O 3 catalyst supplied data on the CO and HC oxidation and NO reduction reactions in environments formed by different reactant combinations (from binary mixtures to the whole mixture simulating the real conditions at the automobile converter). The obtained results have shown notable variations in the oxidation/reduction mechanisms depending on the presence (or absence) of components in the environment. The presence of water always promoted the three-way activity of the catalyst. The compensation effect applied to the CO, NO and HC conversions confirmed that kinetic expressions obtained with partial mixtures (not very close to the real converter environment) have only limited application for determining the whole kinetic scheme occurring in the automobile converters.

The deactivation of protonic zeolites in the catalytic oxidation of 1,2-dichloroethane (DCA) was evaluated. DCA oxidation reactions were carried out in a conventional fixed-bed reactor at atmospheric pressure under conditions of lean DCA concentration in air (1000 ppm). The outlet composition was analysed by a gas chromatograph, an IR spectroscopy-based analyser and another UV analyser. The effect of the zeolite crystalline structure was examined in order to track the catalytic stability of H-ZSM-5, H-MOR and H-BEA under typical reaction environment and conditions (1000 ppm DCA, 300 °C, 13,500 h−1). With the aim of a better understanding of the deactivation pathway, the influence of the space velocity and temperature on the durability of protonic zeolites was analysed. Since some products formed during reaction could also cause deactivation, H2O and HCl were introduced in the feed stream along with the DCA itself, so as to evaluate their effect. In general terms, coke formation was concluded to be the main reason for zeolite catalyst deactivation. Coke was formed from the intermediate vinyl chloride (VC), which resulted from a first dehydrochlorination step of DCA.

The catalytic activity of Pt on alumina catalysts, with and without MnO x incorporated to the catalyst formulation, for CO oxidation in H 2 -free as well as in H 2 -rich stream (PROX) has been studied in the temperature range of 25–250 °C. The effect of catalyst preparation (by successive impregnation or by co-impregnation of Mn and Pt) and Mn content in the catalyst performance has been studied. A low Mn content (2 wt.%) has been found not to improve the catalyst activity compared to the base catalyst. However, catalysts prepared by successive impregnation with 8 and 15 wt.% Mn have shown a lower operation temperature for maximum CO conversion than the base catalyst with an enhanced catalyst activity at low temperatures with respect to Pt/Al 2 O 3 . A maximum CO conversion of 89.8%, with selectivity of 44.9% and CO yield of 40.3% could be reached over a catalyst with 15 wt.% Mn operating at 139 °C and λ = 2. The effect of the presence of 5 vol.% CO 2 and 5 vol.% H 2 O in the feedstream on catalysts performance has also been studied and discussed. The presence of CO 2 in the feedstream enhances the catalytic performance of all the studied catalysts at high temperature, whereas the presence of steam inhibits catalysts with higher MnO x content.

A number of experiments were carried out with fresh and aged high surface area Ce 0.68 Zr 0.32 O 2 mixed oxide samples with complex feed-streams in order to determine their performance as three way catalyst (TWC). The results confirmed the oxygen storage capacity (OSC) of these samples, which favour NO conversion in cycled versus stationary stoichiometric operation. Several experiments carried out with different feed-streams have shown that a pre-reducing treatment can significantly improve both NO reduction at low-temperature and selectivity to N 2 , which can be very useful to reduce the emission of nitrogen oxides immediately after starting the automobile. Although a significant reduction of the specific surface area of the mixed oxide takes place during ageing at 1173 K, it has been shown that the performance of the sample remains similar or even better than when fresh, due to an increased OSC. Thus, the reduction of CO and hydrocarbon emissions during start could be achieved by situating the catalytic converter nearer the exhaust to the engine, where the catalyst will be heated faster.

The activity of cerium/zirconium mixed oxides for TWC applications submitted to different thermal treatments under oxidising, reducing and redox-cycled atmospheres has been investigated. The effect of each individual reactant in the reaction system has been studied using feedstreams in which some components had been removed and substituted by nitrogen. The conclusions extracted from the individual reactions have been used to describe the role and effect of each reactant when all the components are present in the feedstream, and to explain the differences observed in the catalytic performance after different treatments. Finally, a Ce/Zr mixed oxide composition has been proposed as the best support for TWC applications.

The complete catalytic oxidation of trichloroethylene (TCE) over alumina-supported noble metal catalysts (Pt and Pd) and in the presence of hydrogen-rich compounds, i.e. water, hexane and toluene was evaluated. Experiments were performed at conditions of lean TCE concentration (around 1000 ppm) in air, between 250 and 550°C in a conventional fixed-bed reactor. Hexane and toluene were added to the feedstream in a concentration of around 1000 ppm and water concentration varied from 1000 to 15 000 ppm. TCE oxidation occurred faster in the presence of hexane and toluene over both catalysts. Over palladium catalysts, water did not alter catalytic activity, whereas over platinum catalysts water enhanced TCE oxidation at low temperatures ( 400°C). Selectivity to HCl was much improved by feeding water as a hydrogen-supplying reactant; 7500 ppm of water enhanced HCl outputs from 39.4 to 78.0% with Pd, and from 37.5 to 58.9% with Pt. Selectivities to C2Cl4, formed by chlorination of the feed, and Cl2 were greatly reduced. On the other hand water promoted complete oxidation of TCE to CO2, and thus reduced selectivity to CO. In the presence of hexane and toluene, formation of HCl was also enhanced. Hexane showed higher inhibition ability than toluene over both catalysts for the C2Cl4 and Cl2 formation. Unlike in the presence of water, selectivity to CO increased, as a consequence of partial oxidation of both hydrocarbons.

The catalytic activity of several cerium/zirconium mixed oxides for TWC applications has been investigated with the aim of optimising the Ce/Zr composition. Their catalytic activity was surprisingly high, considering that no noble metal was present in the composition, particularly for oxidation reactions (CO and C3H6), while their reduction activity was very small (NO). The specific activity of the mixed oxides for CO and C3H6 was found to be the contribution of the individual specific activity of the single oxides. The best activity in practice (lowest T0 and T50 and highest X773) was found for the mixed oxide with a Ce/Zr ratio of 80/20, as a combination of its high specific activity and the highest specific surface area.

The influence of water and the nature of the hydrocarbon -methane, ethylene, propene and 1-butene- processed in the feedstream on the three-way behaviour of a ceria-modified alumina supported platinum catalyst is investigated. Experiments were carried out with static feedstreams with air-to-fuel ratios between 14.13 and 15.17 as well as with oxidizing-reducing cycled feedstreams simulating the real automobile exhaust mixture. Conclusions are drawn on the importance of water-gas shift and steam reforming reactions and their relationship with inhibition self-poisoning effects of carbon monoxide and/or hydrocarbons. Comparison of data of the prepared catalyst and those obtained at the same operational conditions with two commercial catalysts, with only platinum/alumina and platinum-rhodium/ceria-alumina respectively, allows confirmation of the effects of ceria and establishes the role of rhodium when added to the catalyst.

The effects of the addition of calcia, ceria and lanthana to alumina-supported platinum catalysts on the simultaneous control of hydrocarbon, carbon monoxide and nitrogen oxide automobile emissions (three-way catalyst behaviour) were analyzed. The activity of the prepared samples was determined with steady-state, reducing and oxidizing, simulated feedstreams as well as with a cycled oxidizing-reducing feedstream averaged at the stoichiometric conditions which resembled the exhaust air/fuel fluctuations in a closed-loop emission control system. Activity of the catalysts was also analyzed after conducting accelerated thermal and chemical ageing in order to test their durability. Under normal operating conditions of the automobile engine, Pt/Al2O3 catalysts promoted by rare-earth oxides are able to achieve high HC, CO and NO conversions. The behaviour of the catalysts in the cold start period was determined by analysis of light-off temperatures and a comparison was made with those corresponding to some commercial samples and others reported in the literature. The catalysts prepared in this work showed lower light-off temperatures than those of commercial and reported Pt/Al2O3 catalysts but these temperatures were not so low as with PtRh/Al2O3. In all cases, the prepared catalysts resulted in a better resistance to accelerated ageing. Samples with ceria showed the best resistance to accelerated ageing.