Glycerol (1,2,3-propanetriol) is a water-soluble biomass-derived polyol with versatile chemical reactivity. [94,96,97] Approximately 100 kg of glycerol per ton of biodiesel in the form of concentrated aqueous solutions (80 wt%) are annually produced worldwide in the biodiesel industry as a byproduct of the transesterification of vegetable oils and animal fats with methanol. [98] The high number of applications of glycerol in different fields such as cosmetics, pharmaceuticals, foods, and drinks cannot ab­sorb the surplus of this compound created by the biodiesel industry. Extra glycerol could be consumed as a fuel in internal combustion engines but, unlike ethanol, glycerol cannot be used blended with gasoline because of its low solubility in hydrocarbons and high viscosity. Furthermore, the purification of crude aqueous glycerol for chemical purposes is costly and energy-consuming. Consequently, new technologies, with potential to up­grade aqueous solutions of glycerol, would be valuable. In this respect, a promising route for glycerol conversion involves the production of syn­gas through aqueous-phase reforming (APR) processes. [99] By means of this route, concentrated aqueous solutions of glycerol can be converted to gaseous H2, CO and CO2 mixtures over supported metal catalysts at mod­erate temperatures (498-548 K). Platinum is the preferred metal for this conversion because it favors C-C cleavage reactions (leading to CO, H2 and CO2) versus C-O cleavage reactions (leading to light hydrocarbons). [73,100] To selectively produce syngas versus CO2-enriched mixtures, re­action conditions and catalytic materials must be selected to control WGS reactions. Thus, by operating with inert materials like carbon as a support (instead of using inorganic oxide supports that can activate water), low total pressures (to avoid high partial pressures of water), and high glycerol concentrations (allowing water to become the limiting reagent in WGS), syngas streams with adequate H2/CO ratios for Fischer-Tropsch synthesis can be produced from aqueous glycerol over Pt/C catalysts. [99]

To allow for coupling of endothermic glycerol reforming with exo­thermic Fischer-Tropsch synthesis in a single reactor, it is crucial that the former process is carried out efficiently at low temperatures. However, under these conditions, the metallic surface of Pt is likely to be saturated with adsorbed CO, [101] thus decreasing the overall catalytic rate. One effective strategy to overcome this limitation involves the utilization of alloys such as Pt-Re and Pt-Ru, on which the strength of adsorption of CO is lower compared to Pt. [102,103] This new route involving low — temperature gasification of aqueous glycerol to syngas integrated with Fischer-Tropsch synthesis represents an interesting alternative to complex BTL approaches (Section 4.1). Thus, unlike biomass gasification, glycerol reforming can be carried out at temperatures within the range employed for Fischer-Tropsch synthesis, thereby allowing effective integration of both processes in a single reactor [104] with improved thermal efficiency (since heat required for endothermic reforming is provided by exother­mic F-T process). Furthermore, concentrated aqueous solutions of glyc­erol (as produced in biodiesel facilities) can be converted to undiluted and impurity-free syngas, thereby eliminating the need for large gasifiers with oxygen-production plants and expensive gas-cleaning units. Thus, unlike BTL, this aqueous-phase route allows for costcompetitive operations at small scale, which is advantageous for the processing of distributed bio­mass resources.

Nitrogen sorption measurements were carried out by a Belsorp-mini II gas analyzer at 77 K. The specific surface area (SBET) was determined by the BET equation (p/p0 = 0.05-0.15). The pore size distribution was determined from the desorption branch of the isotherm using the Bar — rett-Joyner-Halenda (BJH) theory. The samples were pretreated at 90 °C while degassing (~0.1 Pa). X-ray diffraction (XRD) measurements were conducted with an ARL X’tra X-ray diffractometer of Thermo Scientific (Waltham, MA, USA) equipped with a Cu Ka1 tube and a Peltier cooled lithium drifted silicon solid stage detector. Raman spectra are recorded using a Raman type FRA106/S spectrometer of Bruker (Karlsruhe, Ger­many), equipped with a Nd-YAG laser (X = 1064 nm).

7.4 CONCLUSIONS

Periodic Mesoporous Organosilica functionalized with sulfonic acid groups has been successfully synthesized and characterized. An ethenylene bridged PMO material was chosen as starting material and this was further post-modified in several steps. A bromination and subsequent substitution reaction was used followed by an oxidation turning the material into a sol­id acid catalyst. This material has been investigated for the acetylation of glycerol. The material showed an equal activity as Amberlyst-15; the lat­ter being usually considered as the reference most-efficient catalyst mate­rial for such kind of reactions. Recyclability experiments showed that the sulfonated Periodic Mesoporous Organosilica is reusable and showed the same total acetylation yield after three runs. Homogeneous tests showed that the acetylation of glycerol indeed occurs heterogeneously, suggesting the absence of leaching, e. g., of sulfonate species, in the medium, and thus the high stability of our material under working conditions.

Biofuels production via the Fischer-Tropsch technology is a conversion process of solid biomass into liquid fuels (Biomass-To-Liquid or BTL) as it is depicted in Figure 2. More specifically the solid biomass is gas­ified in the presence of air and the produced biogas rich in CO and H2 (synthesis gas), after being pretreated to remove coke residues and sulfur compounds, enters the Fischer-Tropsch reactor. The Fischer-Tropsch re­actions allow the catalytic conversion of the synthesis gas into a mixture of paraffinic hydrocarbons consisting of light (C1-C4), naphtha (C5-C11), diesel (C12-C20) and heavier hydrocarbons (>C20). Even though the Fisch- er-Tropsch reactions yields depend on the catalyst and operating param­eters employed [43-45], the liquid product (naphtha, diesel and heavier hydrocarbons) yield is high (~95%). The produced synthetic naphtha and diesel fuels can be used similarly to their fossil counterparts. The heavier product however, which is called as Fischer-Tropsch wax, due to its waxy/ paraffinic nature should get upgraded via catalytic hydrocracking to get converted to mid-distillate fuels (naphtha and diesel).

The conversion of Fischer-Tropsch wax into mainly diesel was studied in virtue of the European Project RENEW [46]. During this project Fisch­er-Tropsch wax with high paraffinic content of C20-C45 was converted into a total liquid product consisting of naphtha, kerosene and diesel fractions via catalytic hydrocracking. However the total liquid product content of diesel molecules was the highest and the diesel fraction was further sepa­rated and characterized having density of 0.78gr/ml and cetane index of 76 [47]. The schematic of the BTL process with actual images of the feed­stock, Fischer-Tropsch wax and synthetic diesel are given in Figure 8.

All reactions were carried out in glass pressure reaction vessels equipped with a magnetic stirrer. The temperature, controlled using an external oil bath, was raised to the desired value (100 °C or 120 °C) and held for the desired time (1 h or 3 h) with vigorous stirring. In a typical reaction, SSA (0.15 g), 1-octene (1.35 g), 1-butanol (0.15 g), phenol (0.94 g), water (0.15

g) , acetic acid (0.15 g), acetaldehyde (0.12 g), hydroxyacetone (0.12 g), D — glucose (0.15 g), 2-hydroxymethylfuran (0.15 g) and the internal standard (99.9% 1-dodecane, 0.02 g) were charged in that order. Catalysts studied included SSA, Cs25/K10, A15, A36 and DX2. After reaction (typically, 3

h) , all products were diluted in methanol and identified by analysis on a Shimadzu QP2010S gas chromatograph equipped with a mass selective detector (GC-MS) using helium as the carrier gas. A SHRXI-5MS (30 m * 0.25 mm I. D. * 0.25 pm film) capillary column was used with a 50:1 split ratio and a solvent cut time of 3 min. The temperature program, started at 30 °C (5 min), was ramped from 30 to 300 °C at 10 °C/min and held at 300 °C for 8 min. An auto-sampler and the same analysis method were used for all product analyses. MS identification of the products was based on molecular mass, fragmentation patterns and by matching the spectra with a digital compound library. The percent phenol conversion to other products in the upgrading reactions was determined by the change in peak area versus that of the 1-dodecane internal standard.

5.4 CONCLUSIONS

Liquid phase supported acid-catalyzed olefin/alcohol reactions with mod­el bio-oils indicate that silica sulfuric acid is an improved catalyst with greater hydrothermal stability and catalytic activity over Cs25/K10 and other resin sulfonic acids. Development and demonstration of this im­proved catalyst meets one goal of this study. Cs25/K10 lost most of its catalytic activity, poisoned by the coke formation from hydroxyacetone,

2- hydroxymethylfuran and D-glucose. Decomposition of resin-bound sul­fonic acids occurred.

The use of different olefins and alcohols leads to different product se — lectivities. This study has demonstrated many of the competing reaction pathways which occur in bio-oil upgrading by acid-catalyzed alcohol/ olefin treatment in much greater detail than all previous work, thereby accomplishing a second major goal of this work. Upgrading bio-oil via simultaneous reactions with olefin/alcohol under acid-catalyzed condi­tions was complex, involving many simultaneous equilibria and compet­ing reactions. These reactions mainly include phenol alkylation, olefin hydration, esterification, etherification, acetal formation, olefin isomeriza­tion and oligomerization, cracking and reoligomerization of tertiary cat­ion centers from protonated olefins and their fragments, hydroxyacetone dimerization (including cyclization) and intermolecular aldol condensa­tion. Also, levulinic acid formation both from sequential dehydration, ring contractions, hydrations and ring opening of monosaccharides, and from sequential rehydration, ring opening, dehydration and tautomerization of 2-hydroxymethylfuran occurred. Synergistic interactions among reactants and products were determined.

somenzation
О efin isomers
Oligomerization
Olefin Oligomers
Olefin
Alcohols
Ethers
R-O-R (RI
-OH
R-O-R ♦ H20
R — C-OR
R-COOH
R-O-R
R — OH	R-O-R
OR* OHR — OH
R — O-R (R) + H20
(‘)R-OH
R*-OH2
RM,-C-OR* ♦ H20
R-COOH
r*-qh|
R — OH
R""
‘RO^H(R…. )
HO OR
Raw ‘ Bio-oil ‘S
R’-OH
о он
ЦПОИ
н2о/н
Hexoses
НОН? С о СНО
но
но. о
V<NOH
о он
он
Bio-oil
FIGURE 2: Reaction pathways of the model bio-oil components during upgrading with olefin/alcohol over solid acid catalysts.

Water removal by acid-catalyzed olefin hydration is the key reason for the success of this upgrading process. As water concentration drops, es­terification and acetal formation equilibria shift toward ester and acetal products. In turn, the formed esters and acetals as well as the added alco­hol help reduce the phase separation present between hydrophilic bio-oil and hydrophobic olefin. All of this occurs while maintaining all the caloric value of both the raw bio-oil and the alcohol and olefin reagents. This work also provides further insight into the complexity of this bio-oil up­grading approach.

1.4.1 PARTICLE SIZE EFFECTS

Within nanocatalysis, the particle size is a well-documented key parameter influencing both activity and selectivity. This reflects the combination of quantum and geometric effects associated with the respective evolution of electronic properties from atomic like to delocalised bands, and shift­ing population of low to high coordination surface atoms, with increas­ing nanoparticle size and dimensionality. Kaneda et al. [130] hypothesised that the unique reactivity of 2060 atom Pd clusters supported on titania towards aromatic alcohol selox arose from a distribution of Pd0, Pd+ and Pd2+ surfaces sites, with n-bonding interactions between the phenyl group and Pd2+ species facilitating subsequent oxidative addition of the O-H bond by neighbouring Pd0 and eventual P-hydride elimination. Surface hydride was hypothesised to react with oxygen from a neighbouring Pd2O centre forming H2O and regenerating the metal site. Optimal activity for cinnamyl alcohol selox to cinnamaldehyde coincided with clusters pos­sessing the maximum fraction of Pd+ character.

Particle size dependency was also reported for the catalytic transforma­tion of benzyl alcohol over Pd nanoparticles dispersed on alumina, SiO2 and NaX zeolite supports [131, 132]. For Pd/NaX and Pd/SiO2-Al2O3, ben­zyl alcohol selox was fastest over particles between 3 and 5 nm, whereas geraniol and 2-octanol were structure-insensitive. Systematic studies of particle size effects in cinnamyl and crotyl alcohol selox over amorphous and mesostructured alumina and silica supports have likewise uncovered pronounced size effects in both initial selox rates and TOFs [133-136], which increase monotonically with shrinking nanoparticle diameters (even down to single atoms) [137]. HAADF-STEM analysis reveals atomically dispersed palladium exhibits maximal rates towards benzyl, cinnamyl and crotyl alcohols, with selectivities to their corresponding aldehydes >70 %. The origin of such size effects is revisited below. The use of colloidal Pd nanoclusters for aqueous phase alcohol selox is limited [138-140], where­in Pd aggregation and Pd black formation hinders catalytic performance. However, the successful stabilisation of 3.6 nm Pd nanoclusters is reported using an amphiphilic nonionic triblock copolymer, Pluronic P123; in the selective oxidation of benzyl alcohol, 100 % aldehyde selectivity and high selox rates are achievable, with high catalytic activity maintained with negligible sintering after 13 recycling reactions [141].

3.4.1 ANALYSIS OF CARBOHYDRATES AND THEIR TRANSFORMATION PRODUCTS

Let us consider first the analysis of a sample of hemicelluloses dissolved in water. The general analytical strategy is given in Figure 10. An ana­lytical procedure using GC based on acid methanolysis consists of the following steps [23]. Freeze drying of a 2 mL solution of hemicellulose in water with the subsequent addition of 2 M HCl in water-free metha­nol, is followed by keeping the sample at 100 °C for three hours of neu­tralization with pyridine, addition of internal standard (sorbitol), evapo­ration, silylation (hexamethyldisilazane and trimethylchlorosilane), and finally GC analysis. The latter could use, for instance, a split injector (260 °C, split ratio 1:15) with a 30 m/0.32 mm i. d. column coated with dimethyl polysiloxane (DB-1, HP-1), hydrogen or helium as a carrier gas and FID with a following temperature programme: 100-280 °C and ramping 4 °C/min.

An advantage of direct methanolysis of wood samples is that essen­tially only hemicelluloses are cleaved and very little cellulose. Moreover, contrary to hydrolysis, it allows less degradation of released monosaccha­rides. Methanolysis can be used also for direct analysis of solid wood and fiber samples. A typical chromatogram is presented in Figure 11, showing several peaks for a particular sugar due to the presence of a & P anomers of pyranoses & furanoses (Figure 12).

Due to the complexity of the product mixture and the analytical pro­cedure correction factors are needed. For instance, cleavage (the meth — anolysis) could be incomplete for certain glycosidic bonds, such as the Xyl-MeGlcA bond. Some degradation of formed sugars, especially uronic acids may happen and the products can have different detector responses. In order to determine correction factors it is recommended to perform methanolysis, silylation and GC analysis on a sample containing equal amounts of Ara, Xyl, Man, Glc, Gal, GlcA, GalA, etc., and pure hemicel­luloses and pectins (if present) and to compare peak areas with the area of the internal standard.

Another example worth considering is the gas-phase catalytic trans­formation of levoglucosan over zeolites [24,25]. The reaction scheme is given in Figure 13. In [24,25] for HPLC analysis an acid Aminex cation H+ column with sulfuric acid (0.005 M) as a mobile phase with a flow of 0.5 ml/min at 338 K was used, along with an Aminex HPX — 87C column and mobile phase-calcium sulfate (1.2 mM) with a flow rate of 0.4 ml/min at 353 K. A refractive index detector was applied. Figure 14 illustrates that the separation is very much dependent on the analytical conditions.

Stability of the samples is another important issue, which should also be carefully considered, as illustrated in Figure 15. Samples stored in a freezer exhibited another peak, which is certainly a result of transforma­tions happening during storage.

An even more prominent difference in analysis was noticed in the aqueous reforming of sorbitol [27-29]. Comparison of the analysis for different columns is given in Figure 16 demonstrating that for the iden­tification of reaction products tedious and time-consuming analytical work is required.

ELS DE CANCK, INMACULADA DOSUNA-RODRIGUEZ, ERIC M. GAIGNEAUX, and PASCAL VAN DER VOORT

9.1 INTRODUCTION

The discovery of Periodic Mesoporous Organosilicas (PMOs) [1-3] with organic bridging groups incorporated in their silica framework has been the start of a fascinating research area which provides materials with huge potential [4-6]. Different organic bridges have been employed for very diverse applications, such as heterogeneous catalysts [7,8], bio-sen­sors [9,10], chromatographic packing materials [11,12], low-k materials [13,14], adsorbents of pollutants [15] and controlled drug delivery sys­tems [16-19]. PMOs are highly porous materials with large specific sur­face areas, pore volumes and narrow pore size distributions. Furthermore, they exhibit a high thermal and mechanical stability [20-22], especially in comparison with other porous silica materials [23]. This type of material is

Periodic Mesoporous Organosilica Functionalized with Sulfonic Acid Groups as Acid Catalyst for Glycerol Acetylation. © De Canck E, Dosuna-Rodriguez I, Gaigneaux EM, and Van Der Voort P. Materials 6 (2013), doi:10.3390/ma6083556. Licensed under a Creative Commons Attribution 3.0 Unported License, http://creativecommons. org/licenses/by/3.0/.

synthesized with structure directing agents such as the non-ionic triblock co­polymer P123. Around this template, a silica source is condensed in basic or acid aqueous environment. Usually, an organo bis-silane (R’O)3-Si-R-Si- (OR’)3 is used where R represents the organic bridging group and R’ usually a methyl or ethyl group. Already many reports have appeared on different bridging groups (R) like phenylene, ethylene, ethenylene and ethylbenzene but also more complex and flexible organic functionalities have been de­scribed. Furthermore the bridging group can be modified to fine-tune the material for a specific application such as solid acid catalysis [4].

Concerning this topic, some very promising results have already been published regarding the incorporation of an acid functionality such as a sulfonic acid group and its catalytic activity. Several diverse methods have been applied to prepare sulfonic acid containing PMO materials. These strategies include the direct sulfonation of the phenylene bridge [24-26], as first attempted by Inagaki et al. [27], and the cocondensa­tion of an organo bis-silane with (3-mercaptopropyl) trimethoxysilane (MPTMS) [28-31] followed by an oxidation of the thiol functionality. The latter can also be achieved by the in-situ oxidation of the thiol func­tionality by the addition of H2O2 during the cocondensation process of tetraethoxyorthosilicate (TEOS) and MPTMS [32,33]. Other silanes have been used in cocondensation processes with an organo bis-silane such as 2-(4-chlorosulfonylphenyl)-trimethoxysilane [34] and perfluorinated al — kylsulfonic acid silanes [35-37].

In the specific case of ethenylene bridged PMOs, — SO3H moieties can be acquired by the direct sulfonation of the C=C bond [38]. However, the sulfonic acid group can detach from the material, depending on the environment used during catalysis. Another explored route is the use of a Diels Alder reaction where the ethene bond acts as dienophile. Kondo et al. [39,40] described the cycloaddition of the ethene bond with ben — zocyclobutene and subsequently the resulting phenylene moiety is sulfo — nated to obtain a heterogeneous catalyst. These authors tested this material for several catalytic reactions (esterification of acetic acid with ethanol, the Beckmann and pinacole-pinacolone rearrangement) and the catalyst showed excellent conversion results. This Diels Alder process has been further used to expand the functionalization possibilities [41].

Another example of modifying the surface of an ethenylene bridged PMO material has been reported by the research group of Kaliaguine [42]. First, the surface silanols were end-capped with hexamethyldisilazane af­ter which a Friedel-Crafts alkylation with benzene was made, and sub­sequently the benzene moiety was sulfonated with concentrated sulfuric acid. The — SO3H containing material exhibited a high catalytic activity in the self-condensation of heptanal.

In this study, the pure trans-ethenylene bridged PMO material [43] is chosen as support material. Thiol functionalities were incorporated ac­cording to a procedure previously described by our research group [44] and subsequently oxidized in order to obtain — SO3H. This material was thoroughly characterized and the solid acid was tested in the acetylation of glycerol. Furthermore, the reusability of this catalyst was investigated.

The straight chain paraffinic molecules resulting from the aforementioned reactions, even though they offer increased cetane number, heating value and oxidation stability in the biofuels which contain them, they also de­grade their cold flow properties. In order to improve the cold flow proper­ties, isomerization reactions are also required, which normally take place during a second step/reactor as they require a different catalyst. Some ex­amples of isomerization reactions are given in Schemes 10 and 11.

R-CH2-CH2-CH3 —— ► R’CH’CH3

CH3

SCHEME 10

Furan compounds such as furfural (2-furaldehyde) and HMFare obtained by dehydration of sugars over mineral acid catalysts such as HCl or H2SO4 at moderate temperatures (e. g., 423 K). These furan compounds find ap­plications as chemical intermediates in the production of industrial sol­vents, polymers and fuels additives. Furfural is obtained by dehydration of C5 sugars like xylose in a well-developed industrial process. [105] On the other hand, the large-scale production of HMF from C6 sugars is more complicated, and several aspects still remain a challenge, one of which is the utilization of glucose as a sugar feedstock. Thus, HMF is typically produced from glucose with low yields, and current technologies include an additional isomerization step to fructose, since dehydration of fructose to HMF takes place with better selectivity and higher rates. [106,107] Fur­thermore, the control over the unwanted side reactions involving the reac­tant, intermediates and the final HMF product is critical. It is particularly important to prevent HMF from overreacting in the aqueous phase, and utilization of biphasic reactors where HMF is continuously extracted into an organic solvent has shown promising results. [108]

Furfural and HMF can be used as building blocks for the production of linear hydrocarbons (in the molecular weight appropriate for diesel and jet fuel) by means of a cascade process involving dehydration, hydrogenation and aldol-condensation reactions, [109,110] as shown in Fig. 7 for HMF. The process starts with acid-catalyzed deconstruction of polysaccharides (e. g., starch, cellulose or hemicellulose) to yield C5 and C6 sugar mono­mers, which are subsequently dehydrated (under the same acid environ­ment) to form carbonyl-containing furan compounds such as furfural and HMF. In a further step, the carbonyl group in the furan compounds serves as a reactive center for C-C coupling through aldol condensation reactions with carbonyl-containing molecules such as acetone, which can be also obtained from biomass-derived sources. [111,112] These condensations are base-catalyzed (e. g., NaOH, Mg-Al oxides) and are typically carried out in polar solvents like water. As a result of the aldol-condensation, a larger compound containing unsaturated C==C and C==O bonds (i. e., al — dol-adduct) is formed and, owing to its hydrophobic character, this adduct precipitates out of the aqueous solution. Recently, improvements have been made in the aldol-condensation process by utilizing biphasic reactors where furan compounds (dissolved in organic THF) are contacted with aqueous NaOH, thus allowing continuous extraction of aldol-adducts into the organic phase. [110] As represented in Fig. 7, the molecular weight of final alkanes can be increased by allowing adducts to undergo a second aldolcondensation process with the initial furanic feedstock. The unsatu­rated C==C and C==O bonds in aldol adducts are subsequently hydroge­nated over metal catalysts such as Pd to yield large water-soluble polyol compounds. The complexity of the process can be reduced by using a bifunctional (metal and basic sites) water-stable Pd/MgO-ZrO2 catalyst. [113] Thus, both aldolcondensation and adduct hydrogenation can be car­ried out simultaneously in a single reactor. The last step of the process involves complete oxygen removal from the hydrogenated aldoladducts to produce liquid alkanes through aqueous-phase dehydration/hydrogena — tion (APD/H) reactions. [114] Oxygen is progressively removed from the water-soluble adducts over a bifunctional metal-acid catalyst by cycles of dehydration and hydrogenation reactions. APD/H can be achieved over Pt-SiO2- Al2O3 in a four-phase reactor involving aqueous solution of ad­ducts, a hydrogen gas inlet stream, a hexadecane sweep stream, and the solid catalyst. [109] The hexadecane stream is important in that it prevents intermediate organic species from overreacting to coke over acid sites. Recently, the utilization of a bifunctional Pt/NbPO4 catalyst, with superior dehydration activity under water environments, [115] has allowed elimi-

nation of the hexadecane sweep stream step and, consequently, production of a pure organic stream of liquid hydrocarbon fuels with targeted molecu­lar weights (C9-C15 for HMF and C8-C13 for furfural) that spontaneously separates from water and retains 60% of the carbon of the initial sugar feedstock. [110]

MARGARITA J. RAMIREZ-MORENO, ISSIS C. ROMERO-IBARRA, JOSE ORTIZ-LANDEROS, and HERIBERTO PFEIFFER

10.1 INTRODUCTION

The amounts of anthropogenic carbon dioxide (CO2) in the atmosphere have been raised dramatically, mainly due to the combustion of differ­ent carbonaceous materials used in energy production, transport and other important industries such as cement production, iron and steelmaking. To solve or at least mitigate this environmental problem, several alternatives have been proposed. A promising alternative for reducing the CO2 emis­sions is the separation and/or capture and concentration of the gas and its subsequent chemical transformation. In that sense, a variety of materials have been tested containing alkaline and/or alkaline-earth oxide ceramics and have been found to be good options.

Margarita J. Ramirez-Moreno, Issis C. Romero-Ibarra, Jose Ortiz-Landeros and Heriberto Pfeiffer (2014). Alkaline and Alkaline-Earth Ceramic Oxides for CO2 Capture, Separation and Subsequent Catalytic Chemical Conversion, CO2 Sequestration and Valorization, VictorEsteves (Ed.), ISBN: 978­953-51-1225-9, InTech, DOI: 10.5772/57444.

The aforementioned ceramics are able to selectively trap CO2 under different conditions of temperature, pressure, humidity and gas mixture composition. The influence of those factors on the CO2 capture (physically or chemically) seems to promote different sorption mechanisms, which depend on the material’s chemical composition and the sorption condi­tions used. Actually, this capture performance suggests the feasibility of these kinds of solid for being used with different capture technologies and processes, such as: pressure swing adsorption (PSA), vacuum swing ad­sorption (VSP), temperature swing adsorption (TSA) and water gas shift reaction (WGSR). Therefore, the fundamental study regarding this matter can help to elucidate the whole phenomena in order to enhance the sor­bents’ properties.