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The carbon dioxide reforming of methane has attracted attention from researchers owing to its possibility of both mitigating the hazards of reactants and producing useful chemical intermediates. In this framework, the activity of the nickel-based catalysts, supported by yttria-stabilized zirconia and promoted with holmium oxide (Ho2O3), was assessed in carbon dioxide reforming of methane at 800 °C. The catalysts were characterized by N2-physisorption, H2 temperature-programmed reduction, temperature-programmed desorption of CO2, X-ray diffraction, scanning electron microscopy (SEM) together with energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) techniques. The effect of holmium oxide weight percent loading (0.0, 1.0, 2.0, 3,0, 4.0, and 5.0 wt %) was examined owing to its impact on the developed catalysts. The optimum loading of Ho2O3 was found to be 4.0 wt %, where the methane and carbon dioxide conversions were 85 and 91%, respectively. The nitrogen adsorption–desorption isotherms specified the mesoporous aspect of the catalysts, while the SEM images displayed a morphology of agglomerated, porous particles. The TEM images of the spent catalyst displayed the formation of multiwalled carbon nanotubes. TGA of the 4.0 wt % of Ho2O3 catalyst, experimented over 7-hour time-on-stream, displayed little weight loss (2O3 and its adjustment of the support.

A preliminary evaluation of the techno-economic feasibility of an industrial glycerol etherification process for bio-additives production has been carried out. The attention has been focused on the etherification reaction in presence of isobutylene (IB) or tert-butanol (TBA) in a batch reactor, catalyzed by an optimized heterogeneous system. Specifically, the Hyflon-based catalyst resulted more efficient and selective to desired products than commercial resin, limiting the competitive reactions of IB oligomerization and byproduct formation. In case of IB, a mixture of poly-ethers, suitable as oxygenated additives for diesel engines, containing very low amount of mono-tert-butylethers ( 85%) was achieved under optimized reaction conditions. The analysis of the whole process demonstrated the techno-economic sustainability of the proposed routes, leading to a production price of glycerol poly-ethers of 1,14 USD/kg and 2,38 USD/kg, by using IB or TBA respectively.

Dry reforming of methane (DRM) for the production of synthesis gas (syngas: H2+CO) was performed over a series of nickel-based catalysts supported on γ-alumina promoted by B, Si, Ti, Zr, Mo and W. All catalysts were prepared by the wet incipient impregnation method and were characterized by X-ray diffraction (XRD), N2 physisorption, H2-TPR, CO2-TPD, XPS, SEM and TGA. Among different catalysts investigated, 5Ni3SiAl and 5Ni3WAl catalytic systems were found highly active with excellent coke resistance in DRM, as both catalyst systems showed >64% CH4 conversion, >70% CO2 conversion, and >0.90 mol H2/CO ratio over seven hours of reaction. The strong interaction between NiO and γ-alumina support in the presence of Si or W oxide modifier (in 5Ni3SiAl or 5Ni3WAl) was indicated as the main factor positively affecting both Ni dispersion and stability.

Abstract The direct hydrogenation of CO2 into dimethyl-ether (DME) has been studied in presence of zeolite-based hybrid catalysts, prepared through gel-oxalate coprecipitation of copper, zinc and zirconium precursors (in an atomic ratio of 60 : 30 : 10 respectively) in a solution containing different home-made zeolites (i.e., Sil-1, MFI, Y, FER, BEA, MOR), for a final CuZnZr/zeolite weight composition of 1:1. All the samples were properly characterized with different techniques for determining the textural, structural and morphological nature of the catalytic surface. N2 physisorption highlighted a variation both in the specific surface area and in the pore size distribution from the parent zeolites to the hybrid catalyst. TEM analyses disclosed how the pre-formed zeolite architecture affects the distribution of the oxides on the surface, significantly controlling not only the activity-selectivity pattern under the adopted experimental conditions (TR, 200–260°C; PR, 30 bar, GHSV: 8.800 NL/kgcat/h), but also the catalyst stability during time on-stream.

A significant boost to the catalytic technology of CO2-to-DME hydrogenation in a single step was recently given by the design of novel hybrid multimetallic/zeolite systems. However, a significant drop of catalyst activity after few hours of operation time pushes now the research interest towards the development of more stable multifunctional systems, suitable to ensure activity, selectivity and lifetime under typical industrial conditions. In this work, the influence of different home-made zeolite samples (i.e., Sil-1, MFI, Y, FER, BEA, MOR), integrated in a weight ratio of 1:1 with a CuO-ZnO-ZrO2 metal-oxide(s) phase, was investigated under long-term stability tests in a fixed bed reactor during CO2 hydrogenation reaction to assess the activity-selectivity pattern of the hybrid catalyst as well as their deactivation trend during operation time. The individuation of key structure-activity relationships helped to explain how the extent of interaction between the metal-oxides phase with the zeolite surface as well as the strength of the acid sites significantly control the catalyst stability.

The oxidation functionality of Mn(IV) sites has been assessed by density functional theory (DFT) analysis of adsorption and activation energies of CO, H2 and O2 on a model Mn4O8 cluster. DFT calculations indicate that Mn(IV) atoms prompt an easy CO conversion to CO2 via a reaction path involving both catalyst and gas-phase oxygen species, while much greater energy barriers hinder H2 oxidation. Accordingly, a MnCeOx catalyst (Mnat/Ceat, 5) with large exposure of Mn(IV) sites shows a remarkable CO oxidation performance at T ≥ 293 K and no H2 oxidation activity below 393 K. Empiric kinetics disclose that the catalyst-oxygen abstraction step determines both CO and H2 oxidation rate, although different activation energies favor the preferential oxidation (PROX) pattern of the studied catalyst (353–423 K). Conversion-selectivity of 100%, high stability during 72 h reaction time and moderate inhibiting effects of water and CO2 feeding reveal the potential of MnO2 materials as efficient, low-cost and robust PROX catalysts.

The hydrodeoxygenation of raw bio-oil was investigated in a continuous fixed bed reactor over a series of FeMoP/zeolite catalysts, pursuing a maximized and stable production of phenolics and aromatics. After 5 h of reaction, the catalysts reach a pseudosteady activity state. The FeMoP/HZSM-5 catalyst yields the highest amount of carbon products (53.5 wt%) with the highest selectivity towards aromatics (13.6 wt%, dry basis) and phenolics (12.2 wt%), due to the synergy between the weak acidity of the FeMoP and the mild acidity of the HZSM-5 zeolite, which minimizes dehydration and gasification. The MFI framework allows the sweeping of coke precursors.

The production of DME via one-pot CO2 hydrogenation is a strategic way of recycling CO2 with the production of a high-value added product. This work aims to investigate the effect of the main zeolite features, e.g. structure or acidity, on the activity, selectivity and stability of the catalyst for DME production via both methanol dehydration and one-pot CO2 hydrogenation. Several zeolites (i.e. FER and MFI) were synthesized and deeply characterized with XRD, B.E.T, NH3-TPD and FTIR. Obtained crystals were used as catalysts for methanol dehydration as well as for one-pot CO2-to-DME process. Obtained results allow giving new insights about the role of the interaction between metals and acid sites for an efficient DME production via one-pot CO2 hydrogenation. In particular, zeolite acidity plays a crucial role in methanol dehydration step and Lewis acid sites seems to be more active than Brønsted sites. Furthermore, metal/acid proximity plays are a key factor in one-pot CO2 hydrogenation; in fact, the catalytic performances of multifunctional catalytic bed improve by increasing the metal/acid sites proximity. The findings of this research allow to highlight the main factors to be taken into account in terms of design and optimization of new catalytic systems for DME synthesis.

The selective N-alkylation of amines with alcohols via the borrowing hydrogen strategy represents a prominent sustainable catalytic method, which produces water as the only by-product and is ideally suited for the catalytic transformation of widely available alcohol reaction partners that can be derived from renewable resources. Intensive research has been devoted to the development of novel catalysts that are mainly based on expensive noble metals. However, the availability of homogeneous or heterogeneous non-precious metal catalysts for this transformation is very limited. Herein we present a highly active and remarkably easy-to-prepare Ni based catalyst system for the selective N-alkylation of amines with alcohols, that is in situ generated from Ni(COD)(2) and KOH under ligand-free conditions. This novel method is very efficient for the functionalization of aniline and derivatives with a wide range of aromatic and aliphatic alcohols as well as diols and exhibits excellent functional group tolerance including halides, benzodioxane and heteroaromatic groups. Several TEM measurements combined with elemental analysis were conducted in order to gain insight into the nature of the active catalyst and factors influencing reactivity.

This paper aims at shedding more light on the reaction mechanism behind the direct hydrogenation of CO2 streams into DME in presence of hybrid catalysts. Starting from the physico-chemical properties of an optimized CuO-ZnO-ZrO2/HZSM-5 catalytic system, whose synergy among active sites of different nature (i.e., metal/oxide and acid/base) was recently proposed as the key to overcome the typical limitations showed by random mixing of two preformed catalysts, new evidences are herewith reported about catalytic performance, conditions for activation of reactants, limiting steps and product formation. Likewise to other proposed mechanisms at the state of the art, the catalyst efficiency is resulted to be dependent on several catalyst features, related not only to the metal-oxide phase responsible for CO2 activation/hydrogenation, but also to specific characteristics of the zeolite (i.e., porosity, specific surface area, population, location and strength of acid sites, interaction with active metals, ...), influencing the activity-selectivity pattern. The production of DME is conditioned by the rate of methanol formation in proximity of the metal-oxide interface, followed by a rapid transferring of methanol towards the neighboring acid sites of the zeolite. Operando spectroscopic investigations performed under simulated reaction conditions (30 bar, 200− 260 ◦C) have shown that the intermediates formation strongly depends upon a concurrence of texture, structure and surface aspects; however, depending on the reaction conditions, methanol formation normally passes through the formation of formate species. From a technological point of view, a re- action pressure of 30 bar appears as the ideal compromise between CO2 conversion and limitation of operative costs, while, due to thermodynamic restrictions, a reaction temperature not higher than 200 ◦C is necessary to attain DME selectivity close to 90 %.

The increasing alarm of global warming always draws interest in reactions like dry reforming of methane (DRM) where both global warming gases (CO2 and CH4) are converted into value-added chemical building blocks, such as syngas. Nickel catalyst active sites along with support acid-base profiles play a key role in DRM. Herein, xLa2O3+(100-x) Al2O3 (x = 0, 10, 15, 20%) supports are prepared and followed by NiO dispersion over the produced support by impregnation method. It was tested for DRM reaction and characterized with TGA, XRD, TEM, IR, Surface area and porosity measurement, H2-TPR, CO2-TPD and NH3-TPD techniques. Upon increasing the basic lanthana proportion in the acidic alumina support, the crystallinity of alumina and acidity of total support decline. Up to 15% Lanthana addition in support claims a low acid and rich basic surface including super basic sites (related to unidentate carbonates) which governed optimum catalytic performance 64% CH4 conversion, 79% CO2 conversion and H2/CO ~ 1 up to 460-min in time on stream test. 20% lanthanum oxide loading led to inferior performance due to rapid loss of surface area, pore-volume, pore diameter, acidity and medium basic strength sites. Fine-tuning of acid-base lanthana-alumina support with dispersed Ni species are a means for understanding DRM.

The influence of the semiconductor microstructure on the photocatalytic behavior of Pt-PtOx/TiO2 catalysts was studied by comparing the methanol-reforming performance of systems based on commercial P25 or TiO2 from sol–gel synthesis calcined at different temperatures. The Pt co-catalyst was deposited by incipient wetness and formed either by calcination or high-temperature H2 treatment. Structural features of the photocatalysts were established by X-ray powder diffraction (XRD), electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS), optical absorption, Raman spectroscopy and TEM measurements. In situ reduction of Pt during the photocatalytic reaction was generally observed. The P25-based samples showed the best H2 production, while the activity of all sol–gel-based samples was similar in spite of the varying microstructures resulting from the different preparation conditions. Accordingly, the sol–gel-based TiO2 has a fundamental structural feature interfering with its photocatalytic performance, which could not be improved by annealing in the 400–500 °C range even by scarifying specific surface area at higher temperatures.

The intermittent nature of renewable resources requires for most applications the development of efficient and cost-effective technologies for steady supply of electrical energy. The storage of energy in the form of hydrogen chemically bound within organic molecules (rather than physically as compressed gas or cooled liquid) represents an alternative approach that is attracting great research interest. Compared to other liquid organic hydrogen carriers (LOHCs), dimethyl ether (DME) appears to have the largest potential impact on society, especially if inserted in technological chains of CO2 sequestration and utilization, so to determine an effective mitigation of environmental issues, without any net effect on the carbon footprint. Specifically, the steps of H2 storage and H2 release can take place in two coupled chemical processes, constituted by the exothermic synthesis of DME via CO2 hydrogenation and the endothermic steam reforming of DME, respectively. Herein, the latest advances in the development of heterogeneous bifunctional and hybrid catalysts for the direct hydrogenation of CO2 to DME are thoroughly reviewed, with special emphasis on thermodynamics, catalyst design and process feasibility. Despite many aspects behind the mechanism of DME synthesis from H2-CO2 streams are still to be uncovered, the recent progress in the research on H2 release by DME steam reforming is increasing the interest for effectively closing this binary H2 loop, in view of future green deals and sustainable research developments.

The formation, growth and transformation of the carbon residue (coke) deposited on the catalyst during the raw bio-oil hydrodeoxygenation have been studied. These deposits have a great impact on the overall process performance, and they have been formed in accelerated deactivation conditions (450 degrees C, 65 bar, space time of 0.09 g(cat) h g(bio-oil)(-1)) using a continuous fixed bed reactor and a FeMoP/HZSM-5 catalyst. Coke deposition causes partial deactivation of the catalyst, which reaches a pseudosteady state of constant activity and also contant yields of interesting chemicals. The evolution of the coke in the transient state has been studied through temperature-programmed oxidation, Raman spectroscopy and elemental analysis. We have identified three different types of coke, whose composition evolves with time on stream towards condensed and stable structures. The assessment of the evolution of the reaction medium composition and the application of the principal component analysis (PCA) methodology have evidenced that the dynamics of coke have three stages: (1) it is controlled by the thermally-induced deposition of thermal lignin; (2) followed by the interconversion into intermediate coke through aging reactions; and (3) it ends up in a pseudosteady state dominated by the formation of catalytic coke species originating from both deoxygenated and carbonized intermediate coke as well as the condensation of aromatics in the reaction medium. This work has been carried out with the financial support of the Ministry of Economy and Competitiveness of the Spanish Government, some co-founded with ERDF funds (CTQ201567425-R, CTQ2016-79646-P), the Basque Government (IT121819), and the European Commission (Horizon H2020-MSCA RISE-2018, Contract No. 823745). Dr Idoia Hita is grateful for her postdoctoral grant awarded by the Department of Education, University and Research of the Basque Government (POS_2015_1_0035).

Applied catalysis / B 272, 118950 (2020). doi:10.1016/j.apcatb.2020.118950, Published by Elsevier, Amsterdam

This research was focused on the valorisation of glycerol, exploring the feasibility of an efficient route for oxygenated additives production based on its etherification with bio-butanol. A home-made BEA zeolite sample with a tuneable acidity has been proposed as the catalytic system, being tested in a stirred reactor under different etherification conditions. Although a reaction temperature as high as 200 °C resulted to be beneficial in terms of glycerol conversion (~90%), only by operating at milder conditions the product selectivity to glycerol-ethers can be better controlled, in order to obtain a bio-fuel complying with the requirements for mixing with fossil diesel or biodiesel, without any need of purification from large amount of by-products. A comprehensive identification of all the compounds formed during the reaction was performed by a GC–MS analysis, on the basis of the complex network of consecutive and parallel reaction paths leading not only to the desired ethers, but also to many side products not detected in similar acid-catalyzed reactions in liquid phase and not available in the most used mass-spectra libraries.

A series of coprecipitated binary Cu-ZrO2 catalysts was found to show an interesting activity–selectivity pattern during methanol synthesis from catalytic hydrogenation of carbon oxides (PR, 20–30 atm; TR, 200–240 °C). The effects of various pre–treatments as well as the copper/zirconia ratio on the structural and chemical properties of these samples were examined. The isoconversional Ozawa-Flynn-Wall method was applied to study the reduction behaviour, while the best fit modelling was used to establish the plausible mechanism of copper reduction. The extent of methanol formation rate was found to be dependent on the structure formed upon catalyst reduction, both in CO and in CO2 hydrogenation conditions. The pre–calcination of the sample at a temperature as high as 650 °C negatively affected the methanol formation rate under CO hydrogenation conditions, while under the same activation treatment an increased specific activity was observed in CO2 hydrogenation conditions, although with a minor methanol selectivity, since the rate of the WGS reaction was stronger enhanced. The incorporation of Zn into the catalyst formulation resulted in a visible increasing of the methanol formation rate, owing to the formation of a copper–zinc mixed oxide during calcination, which leads to higher metal dispersion also depressing the methane formation rate.

The modification of the physicochemical properties of synthetic zeolites is an important element when these materials are applied as heterogeneous catalysts in the view of more sustainable and effective processes. In this work, desilicated ZSM5 samples were tested on the methanol to dimethyl ether dehydration. Desilication time strongly affects the textural and acidic properties of the samples, and those characteristics determined a different catalytic behaviour. Contact time of 60 min with NaOH solution (alkaline desilication) favourably impact on the activity of the catalysts and its stability against deactivation in terms of methanol conversion and yield to DME, in comparison with parent zeolite and sample prepared after 30 min of desilication. This effect is due to a combination of changes in the properties of acidic sites and mesoporous volume, as confirmed by stability test over 80 h of reaction. The analysis of formed coke confirmed this evidence since the most performing catalyst showed the lowest tendency to form coke as the main consequence of the improved accessibility to the acid sites determined by the induced mesoporosity.

Ternary CuxZnyAlz catalysts were prepared using the hydrotalcite (HT) method. The influence of the atomic x:y:z ratio on the physico-chemical and catalytic properties under CO2 hydrogenation conditions was probed. The characterization data of the investigated catalysts were obtained by XRF, XRD, BET, TPR, CO2-TPD, N2O chemisorption, SEM, and TEM techniques. In the &ldquo, dried&rdquo, catalyst, the typical structure of a hydrotalcite phase was observed. Although the calcination and subsequent reduction treatments determined a clear loss of the hydrotalcite structure, the pristine phase addressed the achievement of peculiar physico-chemical properties, also affecting the catalytic activity. Textural and surface effects induced by the zinc concentration conferred a very interesting catalyst performance, with a methanol space time yield (STY) higher than that of commercial systems operated under the same experimental conditions. The peculiar behavior of the hydrotalcite-like samples was related to a high dispersion of the active phase, with metallic copper sites homogeneously distributed among the oxide species, thereby ensuring a suitable activation of H2 and CO2 reactants for a superior methanol production.

The catalytic behaviour of a CuZnZr-FER hybrid catalyst was assessed in the direct CO2-to-DME hydrogenation reaction, considering the effects of structural and surface properties induced on the system by homemade ferrierite samples at different acidity and grain size. Notwithstanding a comparable initial activity under the adopted experimental conditions (TR = 220–260 °C; PR = 3.0 MPa; GHSV = 8800 NL/kgcat/h), the investigated catalyst samples exhibited a different behaviour in terms of stability, with a progressive decay with time mostly marked on the hybrid containing ferrierite at larger acidity. Irrespective of the zeolite grain size, TEM analysis showed a low tendency of catalysts to form carbon deposits, while the comparison of surface properties of “fresh” and “used” samples evidenced a significant metal sintering occurring during reaction, proportional to the Si/Al ratio. The loss of metallic surface area was mainly connected to water formation, as proved in the measurements at high contact time in which a larger net drop between initial and final DME yield, resulting from a higher partial pressure of water, was recorded.

The use of novel nickel based catalysts for the catalytic hydrotreatment of pyrolytic sugars, the carbohydrate rich fraction of pine derived pyrolysis liquids, is reported. The catalysts are characterized by a high nickel loading (38 to 57 wt%), promoted by Cu, Pd, and/or Mo and a SiO2 based inorganic matrix. Experiments were carried out at 180 degrees C and 120 bar initial hydrogen pressure (room temperature) in a batch reactor set-up to gain insight in catalyst activity and product properties as a function of the catalyst composition. The most promising catalyst in terms of activity, as measured by the hydrogen uptake during reaction, was the Ni-Mo/SiO2-Al2O3 catalyst whereas the performance of the monometallic Ni/SiO2-Al2O3 catalyst was the lowest. As a result, the product oil obtained by the bimetallic Ni-Mo catalyst showed the highest H/C ratio and the lowest molecular weight of all catalysts tested. A detailed catalyst characterization study revealed that addition of Mo to the Ni catalyst suppresses the agglomeration of nickel nanoparticles during the catalytic hydrotreatment reaction.

The direct conversion of ethanol to higher value 1-butanol is a catalytic transformation of great interest in light of the expected wide availability of bioethanol originating from the fermentation of renewable resources. In this contribution we describe several novel compositions of porous metal oxides (PMO) as highly active and selective catalysts for the Guerbet coupling of ethanol to 1-butanol in the temperature range 180-320 degrees C. The novel PMO catalysts that do not contain any noble metals are obtained by calcination of a series of hydrotalcite precursors synthesized through modular procedures. In particular, catalyst compositions simultaneously containing Cu and Ni dopants have shown excellent catalytic activities. Up to 22% 1-butanol yield at 56% ethanol conversion was reached in a batch mode; recycling and leaching tests showed excellent robustness of the new catalysts. An extensive characterization by means of several techniques such as powder XRD, SEM, TEM, BET, and NH3- and CO2-TPD was performed in order to understand structure-activity trends.

An easy and cost-effective method to prepare mono-disperse carbon microspheres via a hydrothermal carbonization process (CHT) under moderate conditions (200 degrees C) has been investigated. The preparation was carried out using glucose in aqueous solution. The results clearly revealed that the procedure employed allowed obtaining amorphous microspheres, 200-300 nm in size, and spheres of 1-2 mu m, characterized by a surface area close to 600 m(2)/g. TEM-EELS and XRD analyses demonstrated that the crystallinity grade of carbon micro-spheres significantly increases after N-2 treatment at 1000 degrees C for 6 h. Moreover, the presence of surface functional groups, revealed by DRIFT analysis, allowed functionalizing the carbon spheres by sample inorganic acid treatment or by inorganic acid treatment followed by impregnation with fluorinated superacid ionomer (Hyflon). These catalytic systems resulted to be very active in glycerol etherification reaction, allowing obtaining, differently from a commercial A15 catalyst, a mixture of tert-butylethers containing a very low amount of side products. (C) 2016 Elsevier B.V. All rights reserved.

Ni based phosphate zirconium catalysts were prepared by impregnation technique and used under CH4 dry reforming conditions. Catalysts (x%Ni/8%PO4–Zr, where x = 5, 10, 15 or 20) were characterized by nitrogen physical adsorption-desorption, X-ray diffraction, temperature programmed reduction, CO2 and NH3 temperature programmed desorption, thermal gravimetric analysis and transmission electron microscopy (TEM-EDAX). Catalysts displayed a typical mesoporous structure and different reducibility grade as a function of Ni loading, diagnostic of a different extent of metal-support interaction. Activity and stability strongly depend upon Ni loading while the best performance was observed for catalyst characterized by a Ni loading of 10 wt%. The CO2-TPD profiles of spent catalysts indicated that such catalyst had more tendency to gasify coke formed over the catalyst surface. TGA analysis of used catalysts quantitatively showed that catalysts at higher Ni loading deactivated as result of huge graphitic carbon formation on catalyst surface. On the contrary, system 10%Ni8%PO4/ZrO2 turns out to be an excellent candidate to conduct the methane reforming reaction with CO2 without coke formation at high CH4 and CO2 conversions. Phosphate play a fundamental role in promoting Ni–ZrO2 interaction which reflects in the stabilization of catalytic system against metal sintering and coke formation.

The direct hydrogenation of CO2 into dimethyl-ether (DME) has been studied in presence of copper-based methanol (MeOH) selective catalysts and a commercial ferrierite-type zeolite [1 - 5]. These Cu-based systems are Cu-Zn-Al/ferrierite (CZA/FER) and Cu-Zn-Zr/ferrierite (CZZ/FER). Both hybrid catalysts, obtained through gel-oxalate coprecipitation (OX) and wet impregnation (WI), and physical mixed catalysts with 1:2 and 2:1 weight ratio [2] were explored to compare the activity and the selectivity of these different systems. MeOH-selective catalysts were prepared with a 6:3:1 atomic ratio. All the samples were properly characterized with different physic-chemical techniques in order to determine the textural and the morphological nature of the surface of the catalysts. Firstly, physical adsorption measurements of N2 were elaborated to assess the surface area and the porosity of the samples. Secondly, X-rays diffraction (XRD) patterns were analysed to identify the nature of the phases of the catalysts. In addition, FESEM and EDS techniques were carried out to investigate the morphology and the atomic composition of the surfaces. Eventually, temperature programmed reduction (TPR) measurements were performed for observing the surface and bulk reduction of metal oxides. The experimental campaign was carried out in a fixed bed reactor using 250-500 ?m catalyst particles. According to TPR measurements, the samples were activated by means of a reducing process at a temperature of 350 °C, at atmospheric pressure for 3 h. The reducing atmosphere was obtained with a H2/N2 molar ratio equal to 1:9. After the activation process, a degreening test was performed (2.5 MPa, 275 °C and 13.6 Nl/kgcat/h) to stabilize the catalyst before the activity tests. This procedure was helpful in order to put in evidence if a fresh catalyst was affected by a strong and fast deactivation in reacting conditions [3]. This method highlighted that hybrid catalysts (i.e. CZZ/FER OX 1:2) seem to be very active for few hours, then their activity decreases up to 50 % before reaching a stable operating condition. On the contrary, commercial CZA/FER-based catalysts were not affected by fast deactivation. The diminishing of performances may be probably due to a rearrangement of the catalyst structures at high temperatures. For these reasons, both reduced and aged catalysts has also to be characterized in order to identify the causes of the deactivation and improve catalyst performance and stability. The activity tests were carried out operating at 2.5 MPa with a temperature ranging from 200 °C to 300 °C with steps of 25 ° C. A hydrogen (H2), carbon dioxide (CO2) and nitrogen (N2) gas mixture with a H2/CO2/N2 ratio of 3:1:1 was fed to the reactor. Besides, three different weighted hourly space velocity (WHSV) were investigated from 6.6 to 20.0 Nl/kgcat/h. The results of the activity tests highlighted that hybrid catalysts are more selective towards methanol and dimethyl-ether also at higher temperatures, because the reverse water gas shift (WGS) reaction is more inhibited. Indeed, CZA/FER catalysts were less selective and produce non-negligible amounts of by-products (i.e. C2 hydrocarbons) at temperatures higher than 275 °C. At low WHSV (6.6 Nl/kgcat/h) the thermodynamic equilibrium was approached from 250 °C, but the cumulative MeOH/DME yield is lower than 80 g/kgcat/h. Whereas, the cumulative yield increases at higher WHSV (20 Nl/kgcat/h) reaching a cumulative yield of 256 g/kgcat/h. The CO2 conversion always rises as the reaction temperature grows up due to the endothermic reverse WGS reaction, which is favoured at higher temperatures. As illustrated in Fig. 1 (CZA/FER 1:2, 13.6 Nl/kgcat/h), DME selectivity is extremely higher than CO selectivity at low CO2 conversions, which implies a lower reaction temperature. In literature [3], hybrid CZZ/FER systems could reach extremely high DME yield of about 600 g/kgcat/h, but the stability of these catalysts is a crucial aspect, which has to be improved. These tests showed that hybrid CZZ/FER catalysts might to be improved exploring different synthesis methods in order to increase their activity at lower temperature and possibly also at lower pressures. However, at the same time, selectivity could be improved at higher temperature for increasing the yield through MeOH and DME. These goals could be achieved by trying to add promoters to the structure of these catalysts, or also changing the active phase of the catalysts.

The production of DME from CO2 hydrogenation is a way of recycling CO2 and it requires the use of a hybrid multifunctional catalyst to efficiently catalyze the two consecutive reaction paths of methanol synthesis and methanol dehydration directly in one single step. The aim of this work is to investigate the utilization of zeolite-based catalysts for dimethyl ether synthesis by assessing the role of catalyst features in both methanol dehydration and one-pot CO2 hydrogenation. Obtained results, discussed in terms of turnover frequency reveal that FER-type zeolite prepared with Si/Al=10 exhibits the best performances during vapor-phase methanol dehydration whilst the efficiency of CO2-to-DME process strongly depends on the way in which metallic and acidic materials are coupled. Single grain prepared via gel-oxalate precipitation of CuZnZr over zeolite crystals exhibit the best performances in terms of CO2 conversion and DME productivity.

In the recent years, bio-oil has been attracting great research attention given its potential as a sustainable source of fuels and platform chemicals. When aiming for the production of chemicals (i.e., aromatics, phenolics), hydrodeoxygenation (HDO) has proven to be a versatile approach for achieving an efficient conversion of the most refractory bio-oil components. In this context, phosphided catalysts are known to provide high HDO activities. However, no studies with raw bio-oil are reported to date.