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Current innovations in microalgae technology include the use of wastewater as a cultivation medium for renewable energy generation and wastewater treatment. In this study, thermal pyrolysis was performed on a co-culture of Chlorella vulgaris and Arthrospira platensis grown in winery wastewater fed continuously into a membrane photobioreactor. The yield and composition of the reaction gases, reaction liquids, and solid residues collected at different reaction times and pyrolysis temperatures were compared with those of the same co-culture grown in its conventional medium. In general, the gaseous fraction resulted rich in combustible compounds. The highest yield in liquid products (55 %) was obtained by thermal pyrolysis of the co-culture grown in winery wastewater at 500 °C. Liquid fraction was made up of a mixture of oxygenated and nitrogenated compounds that are suitable as chemical intermediates and can therefore contribute to making the pyrolysis treatment economically feasible. For example, this fraction resulted particularly rich in crotonic acid, useful for the synthesis of copolymers (crotonic acid-vinyl acetate) and probably derived from the thermal cracking of polyhydroxy alkenoate. The results of this study suggest that thermal pyrolysis may be a good strategy to recover the energy potential of microalgae co-cultures used to treat wastewater. Graphical abstract

Copper based catalysts are central for carrying dehydrogenation reactions. However, these materials are prone to deactivation by sintering and coke deposition. Irreversible sintering occurring during reaction (under the effect of temperature) is known to decrease both activity and selectivity, where the unwanted dehydration activity of the support might also play an important role. From this perspective, the quite unreactive silica supports may be attractive. However, using classical catalyst preparation methods (e.g. impregnation), it is a challenge to obtain a stable and homogeneous dispersion of Cu over SiO2 owing to the weak support-active phase interactions. Taking a sidestep, aerosol-assisted sol-gel is a promising alternative for the facile preparation of mesostructured metallosilicates with high metal dispersion. Here we report, for the first time, Cu-SiO2 made by the aerosol-assisted sol-gel method and exploited in the ethanol non-oxidative dehydrogenation to acetaldehyde. These catalysts are compared with a series of catalysts made by impregnation to investigate, through a thorough characterization survey, the effect of the synthesis procedure as well as the effect of Cu loading. We show that aerosol-made catalysts do not suffer heavy sintering, reach high ethanol conversions with acetaldehyde selectivity above 75%, and only slowly deactivate upon time due to a (reversible) coking phenomenon.

Commercial pure γ-Al2O3 and SiO2 (1−30 wt.%) doped γ-Al2O3 were characterized as acid catalysts in ethanol conversion and used as supports for NiO and MoO3. Supported catalysts were prepared by incipient wetness impregnation. All catalytic materials were characterized by BET, XRD, FE-SEM microscopy, UV–vis and IR spectroscopies. Pure and silica-doped NiO/Al2O3 materials were used as precursors of metal catalysts for CO2 hydrogenation. Pure and silica-doped MoO3/Al2O3 materials were used as catalysts for ethanol oxidative dehydrogenation to acetaldehyde. These data show that the addition of silica in moderate amounts selectively influences a part of the alumina surface and strongly modifies the dispersing properties of alumina support. In particular, silica preferentially bonds over the strongest Lewis acid-base sites of γ-Al2O3, where also Ni2+ and molybdate species tend to interact. Being the SiO2-Al2O3 interaction stronger than the NiO-Al2O3 interaction and the MoO3-Al2O3 interaction, silica displaces nickel and molybdate species to less preferential sites where their interaction with exposed alumina is weaker. This results in more easily reducible Ni2+ species and larger Ni metal particles for silica doped Ni/Al2O3, and more monomeric and less polymeric molybdate species for silica doped MoO3/Al2O3.

Two 20 wt.% Co/SiO2 catalysts have been prepared using silica gel as a support and cobalt acetate or nitrate as precursors. They were characterized before and after reaction using XRD, skeletal IR and DR-UV–vis-NIR spectroscopies and FE-SEM microscopy. Fresh catalysts are active in CO2 methanation at atmospheric pressure but rapidly deactivate at 623–673 K, due to formation of encapsulating carbon. However, they retain a more stable activity in producing CO by the reverse water gas shift (rWGS) reaction. Methanation and rWGS appear to occur on independent sites. The Co/SiO2 catalyst produced from Co-acetate precursor shows stable activity in Ethanol Steam Reforming (ESR) at 873−973 K, producing also carbon whiskers (nanotubes) that, however, do not cause catalyst deactivation at the laboratory conditions and timescale. The catalyst produced starting with Co-nitrate is even more active in ESR but it deactivates fast. At lower temperature or when deactivated with respect to ESR, both catalysts shift to high activity in ethanol dehydrogenation to acetaldehyde, showing that the ability to activate water is mostly lost. The differences observed among catalysts produced from cobalt acetate and cobalt nitrate precursors can be associated to the different pH of the impregnating solution. The higher pH of cobalt acetate solution results in surface dissolution / hydrolysis of silica and this may be at the origin of the formation of cobalt silicate surface species, which can also stabilize the support against high temperature reactivity. This might favor larger Co particles formation, less active, but also giving rise to inert cobalt species.

A side-stream ammonia stripping system coupled with a full-scale anaerobic digestion plant is considered. The system is based on an ammonia stripping unit (thin film evaporator, TFE), a Venturi scrubber and a reactive absorption column. A portion of the sludge treated in the digesters is continuously withdrawn and transferred to the TFE, where ammonia is stripped through a biogas stream. The ammonia rich biogas is then treated with a sulfuric acid/water solution in the Venturi scrubber and in the absorption column, with production of an ammonium sulfate solution, which is stored in a tank until utilization as a fertilizer. The aim of this paper is to provide a comprehensive engineering framework supporting the design of a full-scale ammonia stripping system with associated ammonium sulfate production, to be coupled with pre-existing anaerobic digestion plants. On the one hand, an analytical equation is proposed for the simulation of ammonia desorption and the design of the ammonia stripping unit as a function of the selected operating conditions of flowrate, temperature and pH. On the other hand, corrosion issues affecting the storage tank are studied. Corrosion tests, carried out on a selected paint system, demonstrate no development of coating degradation or disbonding, even if local damage occurs in the film. Thus, guidelines to avoid corrosion are given.

The applications of silica-aluminas in industrial catalytic processes are briefly reviewed. The literature data on the surface chemistry and structural chemistry of silica-aluminas are summarized. The Al-stuffed amorphous silica model is proposed for fully amorphous materials, and described. The reasons for the versatility of these materials as acid or acido-basic catalysts as well as tunable supports for metal and sulphide catalysts are also discussed.

Solid acids are the green alternative for heterogeneous acid catalysis, in particular for industrial processes exploiting biomass. Niobium–phosphorus oxides are valid candidates owing to their specific acidic properties and tolerance to water, on the other hand their synthesis often involves hazardous precursors and complex multistep procedures. We have recently employed Nb2Cl10 and POCl3 to synthesize Nb–P–Si mixed oxides with SiO2 content equal to 95 and 92.5 mol% and Nb/P molar ratios equal to 1 and 2, which showed remarkable catalytic activity and water stability in different biorefinery reactions. Here we propose a more sustainable hydrolytic sol–gel route to obtain these materials, starting from ammonium niobium oxalate hydrate and phosphoric acid. The one-pot procedure occurs in water at room temperature, with safe, available and inexpensive precursors, and does not require any catalyst, additive or organic solvent resulting in an energy-efficient protocol. The structural characterisation of the gel-derived solids, performed by FTIR, Raman and 29Si–31P solid state NMR spectroscopies, demonstrates that the designed procedure affords homogeneous samples at the microscopic level with good reproducibility, thus it represents a viable green route for the development of efficient biomass conversion catalytic cycles. Preliminary acid site characterisation and flow reactor experiments in gas-phase ethanol conversion to ethylene demonstrate that these catalytic materials are strongly acidic.

Amorphous catalytic materials belonging to the Nb2O5–P2O5–SiO2 system were prepared through an original sustainable sol-gel procedure, and characterized by surface area, porosity and acidity measurements. Their acid properties have been investigated by FT-IR spectroscopy of adsorbed pyridine, ammonia titration and TPR, as well as by titration with 2-phenylethylamine from organic solution. They present Lewis acidity attributed to niobium surface cationic centers, and Brønsted acidity sufficiently strong to protonate pyridine. The total acidity depends on the niobium content. The conversion of ethanol was investigated by vapor phase Temperature Programmed Reaction, steady-state catalytic experiments and static In Situ FTIR experiments. The samples are active in converting ethanol to ethylene with 100% selectivity at low conversion (523–573 K), but also produce acetaldehyde by dehydrogenation at higher temperature and conversion. They show an unusually poor activity for the production of diethylether also at low ethanol conversion. Ethoxy groups act as reaction surface intermediates.

A series of manganese base oxides (MnCe, MnZr and MnCeZr) obtained by co-precipitation, were characterized by SBET, XRD, TPR, XPS and studiedby FTIR in the oxidation reaction of a typical Cl-VOC such as chloroform, CHCl3. The oxides were compared with a manganeseoxide obtained from the recycling of spent batteries (MnOx). In addition, the catalytic combustion of CHCl3 in a fixed-bed reactor was analyzed and the CHCl3 conversion decreased in the order: MnZr > MnOx = MnCeZr >MnCe. In all cases, the conversion is higher than that obtained without a catalyst. The surface Mn4+/Mn3+ ratio would favor the decomposition of Cl-VOC. The study of CHCl3 reaction atmosphere by in situ IR reveals that in the absence of catalysts, CCl4, COCl2, C2Cl4 and CH2Cl2 were observed. On the other hand, C2Cl4 is not formed in the presence of catalysts, although CCl4 and CH2Cl2 were observed and must be avoided

CO₂ methanation is a very promising technology for the production of alternative fuels with the simultaneous use of greenhouse gases. Therefore, intensive research is carried out on the optimization of catalysts with excellent properties for operation in the area of low temperatures. Here, we present research on a catalyst composed of 19 wt % NiO supported on alumina/calcium aluminate. The catalyst was modified with V₂O₅ in order to be suited for extrusion and scale-up in the frame of power to gas technology. Samples with various vanadium contents (Ni–xV, where x represents the amount of vanadium) were prepared in the form of ground granules obtained from 0.5 mm diameter spherical grains. X-ray diffraction (XRD), transmission electron microscopy (TEM), skeletal infrared (IR), diffuse reflectance ultraviolet–visible-near-infrared (DR-UV–vis-NIR), and X-ray photoelectron (XPS) spectroscopies, as well as H₂ temperature-programmed reduction (H₂-TPR), were used to characterize the samples. Catalytic performances of the catalyst samples were tested in CO₂ hydrogenation at 1 atm. Among the many supported Ni catalysts tested in our laboratories, the catalysts of 0.5 and 1 wt % V showed very high activity, with the highest CH₄ yield of 97% at 623 K. These catalysts exhibited 100% CH₄ selectivity up to 673 K. The excellent performances of the studied catalysts are attributed to the possible formation of Ni–V solid solution alloy nanoparticles.

The waste materials available as sources of silicon and aluminum for producing porous materials like amorphous silicas, aluminas, amorphous silica-aluminas, and zeolites, to be used as catalyst and adsorbents, are briefly summarized. The procedures for preparing these materials from wastes are also taken into account. The limits of this approach in terms of economy and environmental protection are also briefly considered. It is concluded that mesoporous materials can be prepared from wastes, but care to product quality and to overall process efficiency is needed.

Two 20 wt.% Co/SiO2 catalysts were prepared using silica gel as a support and cobalt acetate and nitrate as precursors, respectively. As a comparison unsupported amorphous cobalt nanoparticles (10–80 nm) were synthesized by decomposing cobalt carbonyl. They were characterized before and after reaction using XRD, IR spectroscopy in the range of framework vibrations, DR-UV–vis-NIR spectroscopies and FE-SEM microscopy. They are active in CO2 methanation at atmospheric pressure. However, unsupported cobalt and the silica-supported catalyst prepared using cobalt acetate deactivate fast at 623–673 K, also due to formation of encapsulating carbon. On the other hand, they retain more stable activity in the reverse water gas shift (rWGS) reaction, producing CO. Methanation and rWGS appear to occur on independent sites. The silica-supported catalyst produced from cobalt nitrate show more stable methanation activity, attributed to the presence of smaller cobalt particles (10–20 nm) that resist deactivation. For both unsupported CoNPs and Co/SiO2, the significant parameters for catalysts deactivation have been determined for CO2 methanation. The differences observed among catalysts produced starting from cobalt acetate and cobalt nitrate, can be associated to the different pH of the impregnating solution.

International audience; The present work reports the feasibility of valorizing waste glass and aluminum scraps into zeotype materials. The raw materials were reacted hydrothermally at 60°C using alkaline fusion prior to hydrothermal treatment. The obtained powders were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM) and magic angle spinning nuclear magnetic resonance (MAS NMR) of 27 Al and 29 Si nuclei. The influence of some parameters like alkalinity, reaction time and particle size on the nature of obtained zeolites has been also studied. The characterization methods demonstrated that the final products are aluminosilicate materials with a high cation exchange capacity containing Na-FAU and Na-P1 zeolites. The above results show that valorization of waste glass and aluminum scraps to obtain Na-FAU and NaP1 zeolites is possible and can be a sustainable alternative to the traditional synthesis methods.

This review begins with the historical development of the theories of acidity and of the preparation of acids. The historical aspects of acid catalysis and catalysts are also briefly surveyed. The fundamentals concerning acidity and acid catalysis in liquid phases and at the solid-liquid interfaces are discussed. The factors determining acidity and activity, as well as practical applicability, of solid catalysts such as protonic zeolites are reviewed in detail. Methods for investigation of surface acidity of solids at both solid/vapor and solid/liquid interfaces are briefly discussed. Finally, most of solid acid families are considered and their properties critically reviewed.

Graphitic carbon nitride (gCN(H)) is a semiconductor with high mechanical and thermal stability which provides good dispersion of metal particles. As it is resistant to corrosion, it constitutes an...

Ethanol is one of the most important organic solvents used as a fuel, chemical, and as an intermediate for organic chemical synthesis. However, its use as a fuel has several drawbacks including corroding the engine, producing lower energy than conventional fuel, and adsorbing water. Hence, it needs to upgrade into a highly efficient fuel such as n-butanol. In addition, the demand for raw materials increases due to the development of current industries such as plastic, solvent, and surfactant industries. However, the fossil resources, the main sources for current raw materials production, are limited and continuously depleted. As a result, the conversion of low-cost biomaterials like bioethanol into high-value raw materials for current industries is a promising perspective. In this chapter, some potential reaction processes in bioethanol conversion including dehydration, oxidation, steam reforming, dehydrogenation, and Guerbet reaction are summarized. These catalytic reactions and ethanol-derived products are discussed to elucidate the current picture of ethanol transformation.

The different types of heterogeneous catalyst currently applied in the chemical industry are described. The catalytic activity is correlated to their main surface properties, which are the object of investigation based on surface science and theoretical calculations. Acidic, basic, oxidation, hydrogenation, and dehydrogenation catalysts are described. Metal, oxide, sulfide, and halide catalytic materials are considered. The practical need for promoters and stabilizers is underlined, frequently resulting in multicomponent and multiphasic catalytic systems. The complexity and multidisciplinarity of the field of heterogeneous catalysis research are emphasized, where collaboration among chemical engineers, material scientists, physical, inorganic, and organic chemists, and surface and material physicists is needed to fully understand phenomena and develop technologies. As a case study, the steam reforming process for producing hydrogen from natural gas is considered. The available data make it clear that knowledge on the molecular phenomena for most industrial processes is still largely incomplete and subject to debate. It is emphasized that surface science and surface chemistry, as well as computational studies, are needed to further improve existing technologies and to apply heterogeneous catalytic processes in the new era of industrial chemistry based on renewables.

Three Ni-based natural gas steam reforming catalysts, i.e., commercial JM25-4Q and JM57-4Q, and a laboratory-made catalyst (26% Ni on a 5% SiO2–95% Al2O3), are tested in a laboratory reactor, under carbon dioxide methanation and methane steam reforming operating conditions. The laboratory catalyst is more active in both CO2 methanation (equilibrium is reached at 623 K with 100% selectivity) and methane steam reforming (92% hydrogen yield at 890 K) than the two commercial catalysts, likely due to its higher nickel loading. In any case, commercial steam reforming catalysts also show interesting activity in CO2 methanation, reduced by K-doping. The interpretation of the experimental results is supported by a one-dimensional (1D) pseudo-homogeneous packed-bed reactor model, embedding the Xu and Froment local kinetics, with appropriate kinetic parameters for each catalyst. In particular, the H2O adsorption coefficient adopted for the commercial catalysts is about two orders of magnitude higher than for the laboratory-made catalyst, and this is in line with the expectations, considering that the commercial catalysts have Ca and K added, which may promote water adsorption.

A mesoporous alumina has been synthetized by a hydrothermal method describe by Ĉejka and al. who use as precursor an aluminium isopropoxide and subsequently calcining the precipitate obtained in nitrogen flow at 683 K for 6h. The structural and morphological study evidence that the alumina obtained is a thermal stable γ-Al2O3 phase up to 1073 K with a specific surface area value of 174 m2g-1. The study of the surface hydroxyl groups in the sample γ-Al2O3 phase calcined at 1073 K (hereinafter called ALMP1073) reveals the presence of three types of active OH groups absorbing at 3787, 3725 and 3690 cm-1 and that they are significantly acidic, but not enough to protonate pyridine., i.e, they can be considered as Lewis acid. Catalytic test in ethanol dehydration prove that the ALMP1073 sample is active and selective in the dehydration of ethanol to diethylether in the range 523-573 K, as well as in the dehydration of ethanol to ethylene in the range 623-723 K These data are consistent with those obtained by infrared spectroscopy. The ethoxy groups formed on the surface of γ-Al2O3 are proposed as intermediate species in the ethanol dehydration reaction for both diethylether and ethylene formation.

Production of propylene, the second-largest petrochemical after ethylene, has received considerable attention in recent years due to its wide applications and avoiding oil dependence. Many processes have been developed to produce propylene from fossil resources and renewable materials. In this review, we will introduce the current processes to produce propylene. In parallel, biopropylene production from bioethanol using a widely used material in petrochemistry, ZSM-5, has also been discussed. The physicochemical properties of ZSM-5 to be applied as an efficient catalyst for this reaction, such as the particle/crystal size, the Si/Al ratio, metal addition, and its stability, as well as reaction conditions and pathways have been discussed to suggest the potential parameters to control the bioethanol dehydration into propylene.

Ni-based catalysts, 13.5 Ni wt.%, with enhanced thermal stability and catalytic performance for CO2 methanation have been synthesized with different La2O3 loadings. Catalysts have been extensively characterised by: XRD, IR, H2-TPR, IPA-TPD, UV–vis-NIR, FE-SEM and tested in CO2 methanation. SiO2 addition to Al2O3 support decreases the activity for CO2 methanation, while lanthanum acts as suitable promoter by strongly increasing catalytic performances. Silica presence successfully inhibits the formation of crystalline perovskites phases, stabilizes support morphology, and allows the introduction of high La2O3 loadings, allowing a better control of acid-base properties. 37 % wt. La2O3 addition gives rise to even higher performances than those previously observed, i.e. 83 % CH4 yield at 573 K. Reaction orders for CO2 and H2 have been determined; La- addition is confirmed to be responsible for a reduction in the CO2 reaction order, suggesting a stronger CO2 adsorption and the possible role of these species as a reactant reservoirs.

The adsorption of water, pyridine, CO and CO2 on a commercial γ-Al2O3 and a commercial amorphous silica alumina (ASA) cracking catalyst are reinvestigated by means of FTIR spectroscopy. It is concluded that the real active hydroxyl groups on γ-Al2O3 are those absorbing at 3790, 3770 and 3730 cm−1 and that they are significantly acidic. The strongest Lewis acid sites are identified as Nuclear Magnetic Resonance (NMR)-silent (or still undetected) tricoordinated Al3+, becoming tetracoordinated when interacting with basic adsorbates. More than one pyridine molecule may adsorb over such highly coordinatively unsaturated sites at high pyridine vapour pressure. It has also been confirmed that the existence of Bronsted acid sites sufficiently strong to protonate pyridine on ASA is its intrinsic property, not due to coadsorbed water. A “stuffed amorphous silica” model is proposed for low-alumina ASA, where part of Al3+ ions compensate the charge in-balance due to the substitution of Al for Si in a silica-like tetrahedral framework. Interstitial Al3+ occupy 4-, 5- or 6-coordination interstices in the amorphous silica-like framework as do alkali cations in “stuffed silicas” aluminosilicates. Such “interstitial” Al3+ ions when located accidentally in opened interstices exposed at the surface play the role of strong Lewis sites. When these ions are located near a silanol group, they increase the Bronsted acidity of the terminal silanols by neutralizing the negative charge produced by their dissociation when interacting with bases.

Spent alkaline and zinc-carbon batteries were subjected to a biohydrometallurgy process, in order to recover manganese and mixed manganese zinc oxides. Two solids were synthesized, one of them prepared by reaction of MnSO4 and KMnO4 (MnOx) and the other obtained by chemical precipitation with NaOH (ZnMnO). The characterization by XRD, TPR, FTIR and XPS revealed the presence of Mn3+ and Mn4+ cations in both samples, and the presence of ZnO and Mn-Zn spinels in ZnMnO. The samples were evaluated in the oxidation reaction of ethanol and toluene. The results in the flow reactor showed that ethanol conversion on both catalysts, MnOx and ZnMnO, is rather similar, but toluene conversion is markedly higher on MnOx, due to a greater Mn/Zn ratio and to the absence of a crystallized ZnO phase. The FTIR study demonstrated that ethanol is oxidized to acetaldehyde at low temperature, and to CO2 and CO at 400 C. Traces of CH4 in the gas phase are also detected at high temperature. The formation of ethoxy and acetate groups is observed at the catalyst surface. With respect to toluene oxidation, CO2 is detected at 300 C and when the temperature is increased, CO is also observed in the gas phase. The results showed that: (i) the alkaline and Zn-carbon batteries can be recycled as catalysts and (ii) the solids can be used in the catalytic process for VOCs control., Centro de Investigación y Desarrollo en Ciencias Aplicadas

Lanthana on alumina samples (0.2, 0.8 and 4.7 theoretical monolayers) were prepared by incipient wetness impregnation using γ-Al2O3 as support. Characterization has been performed by BET, XRD, skeletal FT-IR, DR-UVvis, XPS, HR-TEM, IR spectra of the surface OH, adsorbed pyridine and CO2, and isopropanol TPD. Ethanol conversion was investigated both in temperature-programmed surface reaction (TPSR) dynamic conditions as well as in steady-state flow reactor tests. Lanthanum addition stabilizes alumina with respect to sintering and loss of surface area and La- containing phases are observed only for the high-La loaded catalyst. La-alumina catalysts are less active in ethanol dehydration than alumina but more selective to diethyl ether at partial conversion. 5%La2O3/Al2O3 is also equally or more selective than alumina to ethylene at high conversion, producing less carbonaceous material during reaction. Thus, this catalytic system might be a good candidate for (bio)ethylene production through (bio)ethanol dehydration.

In this work, winery industry wastes were valorised through the extraction of high added value compounds (polyphenols), followed by thermal conversion of the exhausted solid residues. For this purpose, three different temperatures (623, 723 and 823 K) were tested. The increase of the heat treatment temperature resulted in a significant increment in gas production containing methane and other hydrocarbons. Lipophilic liquid product quantity in grape marc was limited both before and after the polyphenol extraction. The recovery of phenolic compounds before the thermal treatment notably decreases the chemical oxygen demand level of the resulting hydrophilic liquid fraction. The pyrolysis residue represents from 30 to 55% of the initial mass but corresponds to a relevant decrease of its volume, and can be considered a good source of graphitic carbon with higher calorific value with respect to the initial grape waste and applicable for energy production.

3% Ru/Al 2 O 3 catalyst is active in converting CO 2 into methane at atmospheric pressure. At 673 K and above the thermodynamic equilibrium is nearly attained. At 623 K CH 4 yield is above 85%. CO selectivity increases by decreasing reactants partial pressure apparently more than expected by thermodynamics. The reaction order for CO 2 partial pressure is confirmed to be zero, while that related to hydrogen pressure is near 0.38 and activation energy ranges 60–75 kJ/mol. Arrhenius plot demonstrates that only at reduced reactant partial pressure (3% CO 2 ) or high contact times, a contribution due to some diffusional limitation is present. IR study shows that the H 2 —reduced catalyst has high-oxidation state Ru oxide species able to oxidize CO to CO 2 at 173–243 K, while after oxidation/reduction cycle the alumina surface acido-basic sites are freed and the catalyst surface contains both extended Ru metal particles and dispersed low valence Ru species. IR studies show that the formation of methane, both from CO and CO 2 , occurs when both surface carbonyl species and surface formate species are observed. Starting from CO 2 , methane is formed already in the low temperature range, i.e., 523–573 K, even when CO is not observed in the gas phase.

The waste materials available as sources of silicon and aluminum for producing porous materials like amorphous silicas, aluminas, amorphous silica-aluminas, and zeolites, to be used as catalyst and adsorbents, are briefly summarized. The procedures for preparing these materials from wastes are also taken into account. The limits of this approach in terms of economy and environmental protection are also briefly considered. It is concluded that mesoporous materials can be prepared from wastes, but care to product quality and to overall process efficiency is needed.

A process for the continuous extraction of ammonia from anaerobic digesters is proposed. In this process, a portion of the sludge treated in the digesters is continuously withdrawn and transferred to a thin film evaporator (TFE) unit, where the ammonia is stripped through a biogas stream. The ammonia-rich biogas is treated with a sulfuric acid/water solution in a reactive absorption unit, with production of ammonium sulphate. The chemistry of a CH4/CO2/NH3 gas phase in thermodynamic equilibrium with a liquid sulfuric acid/water solution is investigated theoretically, with focus on the simultaneous absorption of CO2 and NH3 into the liquid phase. Pilot plant experimental data confirm the theoretical results. Further pilot plant experimental results obtained during on-off cycles of the stripping equipment demonstrate that, when the TFE unit is off, ammonia concentration in the digestate rises quickly, while, when the stripping equipment is turned on again, ammonia concentration drops down. On average, during the 180 days of pilot plant experimentation, 4.1 g N–NH4 per kg of sludge fed to the digester, i.e. 19.3 g N–NH4 per kg of total solids (TS) fed to the digester, are stripped from digestate and recovered as ammonium sulphate, demonstrating the feasibility of the proposed concept.