Two Cu-Zn-Al catalysts prepared by the coprecipitation method, both differing in their type of structure, one as a mixed oxide (polymetallic catalyst) and the other as a hydrotalcite-like catalyst, were used for the synthesis of methanol by hydrogenation of CO2 in a fixed bed reactor system, operating under conditions of low pressure (6 bar) and temperature of 265°C. The effect of the composition of the catalyst on its catalytic activity under low pressure conditions was investigated. The main results show that the highest CO2 conversion is found with Cu-ZnAl polymetallic catalyst, however, the best selectivity to methanol is shown for Cu-Zn-Al hydrotalcite-like catalyst.

The Canary Islands, renowned for their tourism appeal, grapple with a pronounced energy challenge stemming from their geographic fragmentation and heavy reliance on external energy sources, particularly fossil fuels. Moreover, the region's history is marked by recurring energy crises, underscoring the imperative need for a swift and decisive transition towards renewable energy sources. This research examines the potential of waste biomass as a renewable energy source in the Canary Islands. This reliance on non-renewable energy sources leads to increased energy costs and greenhouse gas emissions, making the pursuit of a sustainable energy future a strategic priority in the region. This study proposes to assess the potential of residual biomass from the main crops of the Canary Islands, such as bananas, tomatoes, potatoes, and grapes, for bioenergy production. Statistical data were used to estimate the total availability of residues, while parameters like residue-to-product ratio, moisture content and calorific value were determined to calculate the energy potential of the residual biomass. The research findings reveal that the annual production of residual biomass from the primary crops in the Canary Islands is 234,744 tonnes (111,425 Tn/year from banana cultivation, 52,961 Tn/year from tomato cultivation, 40,102 Tn/year from potato cultivation, and 30,256 Tn/year from grape cultivation). This biomass has the potential to generate around 1.39 PJ of energy, equivalent to approximately 4.79% of the current energy consumption of the archipelago. Considering that renewable sources contribute to only around 20% of the energy production in the Canary Islands, the availability of this resource presents an exceptional opportunity for the region. By harnessing its natural resources, the Canary Islands can pursue sustainable economic growth while simultaneously mitigating negative environmental impacts. Definitely, the assessment of the potential of residual biomass plays a crucial role in evaluating sustainable energy resources and represents an important step towards a more sustainable energy future in the Canary Islands.

This work presents a study of synthesis and characterization of catalysts-based cerium and nickel supported on the pumice stone (Ce/Pumice and Ni/Pumice) to be used in the gasification process of an invasive species present in the Canary Islands, such as Pennisetum setaceum to obtain syngas. Specifically, the effect of the metal impregnated on the pumice, and the effect of catalyst on the gasification process was studied. For this purpose, the composition of the gas was determined and the results obtained were compared with those obtained in noncatalytic thermochemical processes. Gasification tests were performed using a simultaneous thermal analyzer coupled with a mass spectrometer, providing a detailed analysis of the gases released during the process. The results showed that during the catalytic gasification process of the Pennisetum setaceum, the gases produced appear at lower temperatures in the catalytic process that in the non-catalytic process. Specifically, H2 appears at 640.42 degrees C and 641.84 degrees C when Ce/pumice and Ni/pumice were used as catalyst, respectively, compared to 697.41 degrees C for the non-catalytic process. Moreover, the reactivity at 50 % of char conversion for the catalytic process (0.34 and 0.38 min-1 for Ce/pumice and Ni/pumice, respectively) was higher than for the non-catalytic process (0.28 min-1), indicating that the incorporation of Ce and Ni on the pumitic material increases the gasification rate of the char compared to the pumitic support. Catalytic biomass gasification is an innovative technology that can provide new opportunities for research and development of renewable energy technologies, as well as for the creation of green jobs.

A packed-bed catalytic configuration reactor using pumice granules loaded with lithium (Li/Pumice) as a heterogeneous catalyst was developed for biodiesel production in continuous. For this purpose, Jatropha curcas oil was used as an alternative feedstock to edible oils and diethyl ether was used as a cosolvent to eliminate the limitations of mass transfer between the phases. In this work, the response surface methodology was applied to optimize the fatty acid methyl esters (FAME) yield in biodiesel production. The flow rate (0.7-1.4 mL min-1), the methanol/oil molar ratio (6:1-20:1) and the cosolvent/methanol molar ratio (0.5:1-1.5:1) were the independent variables studied. The effects of these factors over the FAME yield using Li/Pumice as catalyst were evaluated according to a Box-Behnken design. The optimum conditions for the maximum FAME yield (100%) were 1.4 mL min(-1), 20.0 methanol/oil molar ratio and 0.57:1 cosolvent/methanol molar ratio.

Tenerife is one of the main islands of the Canary Islands, which, due to its characteristics as outermost region, has a high energy dependence as well as a limitation on available territory; in addition, as it has been designated as a Remote Area, the elimination of Animal By-Products (ABPs) in landfills is permitted. This treatment does not contribute to the current trend of a circular economy and negatively harms the environment. The energy recovery of this waste through anaerobic digestion to produce biogas would enhance the use of renewable energies, contributing to the meat industry's energy independence and better management of the waste generated by this industry in Tenerife, promoting an energy transition towards cleaner energies. The study of the potential for biomethanization has been carried out both separately and in co-digestion in search of the best biogas production. Of the samples studied, only biogas was obtained in the anaerobic digestion of the rumen content, sewage sludge and for the co-digestion of viscera (cattle, pigs, goats, sheep, and rabbits) with raw blood and sewage sludge. The latter produces 128 mL of biogas per gram of volatile solids (VS) of the mixture, resulting in a total of 4,800 kWhe of electrical energy for Tenerife's estimated waste in 2019.

The skeletal isomerization of I-butene was performed over a series of metal (Cr, Zn) substituted silicoaluminophosphate molecular sieves (SAPO-11, CrAPSO-11 and ZnAPSO-11 solids). For times-on-stream under 2.5 h, the CrAPSO-11 catalyst showed a higher skeletal isomerization efficiency (SIE) than the two prepared SAPO-II samples and a supported Cr/SAPO-11 system. After 2.5 h a drastic decrease in the SLE occurred (for the CrAPSO-11 sample) with a concomitant increase in the formation of butadiene and 2-butenes. The results were in line with the acidity measurements, particularly at low times-on-stream (TOS). At higher TOS reduction of Cr (VI) occurred with a concomitant decrease in the catalyst acidity. The ZnAPSO-11 solid turned out to be more acid and selective than the parent SAPO-11 molecular sieve. The results are discussed in terms of different incorporation models for the corresponding metals.

A series of substituted AlPO4 molecular sieves with the AEL topology were prepared and characterized by different techniques, to evaluate the amount and nature of the additional elements and their effect on the acidity and catalytic properties of the resulting solids. It was found that a one-to-one interaction between Lewis (L) and Brønsted (B) sites occurs after calcination of the substituted materials, leading to an enhanced acidity and causing, as a result, an increase in the selectivity towards isobutene during the transformation of 1-butene. Substitution models are discussed in order to rationalise the origin and nature of such B-L synergism.

Ga-71 MAS n.m.r. analysis and the catalytic behavior during the transformation of l-butene and n-butane strongly suggest the incorporation of Ga into the AIPO(4)-11 (AEL) framework during the synthesis of GaAPSO-11. A unique clear signal at around +120 ppm is proposed to be associated with the presence of tetrahedral Ga in the AEL framework of the unmodified GaAPSO-11. Migration of structural Ga atoms to the silicon domain of the AEL framework seems to occur as a result of a mild hydrothermal treatment, giving rise to an additional signal at +156 ppm, previously associated with tetrahedral gallium in gallosilicates with the MFI topology. The fact that GaAPO-11 and GaAPSO-11 behaved in a way similar to their counterparts AIPO(4)-11 and SAPO-11 during the skeletal isomerization of n-butenes reinforces the idea of an isomorphous substitution of Al(III) by Ga(III) in the AEL framework. The transformation of n-butane was shown to be a valuable test for detecting the presence of small amounts of hydro-dehydrogenating extraframework gallium species (EFGS) in Ga-supported SAPO-11 (Ga/SAPO-11). The fact that the sample of GaAPSO-11 was completely inactive for Eh is transformation leads us to believe that the incorporation of gallium into the tetrahedral positions of the AEL framework was almost complete. (C) Elsevier Science Inc. 1997.

The catalytic transformations of 1-butene were performed over a chromium-substituted silicoaluminophosphate molecular sieve (CrAPSO-11), over a Cr-supported SAPO-11 molecular sieve (Cr/SAPO-11), and over two SAPO-11 samples. For times-on-stream under 2.5 h, the CrAPSO-11 catalyst showed a higher skeletal isomerization efficiency (SIE) than the two prepared SAPO-11 samples and the supported chromium system. After 2.5 h a drastic decrease in the SIE occurred (for the CrAPSO-11 sample) with a concomitant increase in the formation of butadiene and 2-butenes. The formation of butadiene was considerably hindered over the supported system compared to that of the CrAPSO-11 sample. The cracking reactions as well as the formation of C5+ hydrocarbons were also suppressed over the supported system. The catalysts were recently characterized by XPS and redox cycles (12) and presently studied by XRD, DRS, and NO chemisorption followed by IR spectroscopy and acidity measurements performed with pyridine chemisorption. A larger amount of Cr(VI) was found by DRS and XPS (∼70%) for the oxidic CrAPSO-11 (O2, 773 K), compared to the supported system. For the latter, Cr(III) was the main species present. The NO chemisorption experiments showed the presence of high chromium oxidation states on the oxidic CrAPSO-11. After reduction (H2, 773 K), the distribution of oxidation states of chromium (XPS and NO chemisorption experiments) for the reduced CrAPSO-11 solid, was different ∼40% Cr(VI) and ∼60% Cr(III) compared to the oxidic sample. Cr(VI) showed a higher stability towards reduction in the CrAPSO-11 catalyst when compared to chromium supported on conventional supports. The distribution of oxidation states of chromium was very similar for the oxidic and the reduced Cr/SAPO-11 catalyst. The oxidic CrAPSO-11 catalyst showed an increase in the number of medium+strong acid sites compared to the other catalysts. The reduction process, however, decreased the Brønsted strong acid sites by a factor of two. A concomitant decrease was observed for the medium+strong Lewis acid sites, upon reduction. These results suggest that a partially unsaturated Cr(VI) in the vecinity of P–OH groups may act as strong Lewis sites, generating Brønsted acidity by Brønsted–Lewis interaction, as suggested in the literature. The supported sample showed a decrease of medium+strong Brønsted acid sites compared to the CrAPSO-11 solid. In this case, however, the reduction process did not cause major changes in the acidity distribution. The characterization as well as the catalytic data support and reinforce the model presented by Chen and Sheldon (J. Catal.153, 1 (1995)) for the related CrAPO-5 system. The results suggest the incorporation of chromium into the molecular sieve framework for the CrAPSO-11 catalyst.

The catalytic transformations of 1-butene were performed over a zinc-substituted silicoaluminophosphate molecular sieve (ZnAPSO-11), over a Zn-supported SAPO-11 molecular sieve (Zn/SAPO-11) and over the unpromoted SAPO-11 solid. The ZnAPSO-11 catalyst showed the highest selectivity towards skeletal isomerization as well as the highest skeletal isomerization efficiency (SIE). In addition, the largest number of acid sites, particularly strong acid sites, were observed with temperature-programmed desorption of ammonia (NH3-TPD) over the ZnAPSO-11 catalyst. The acid strength over the latter was also the highest. The agreement between the catalytic and the acidity results obtained in the present work can be explained in terms of the model of Gielgens et al. In this model, the substitution of Al(III) ions by Zn(II) ions leads to partially unsaturated Zn(II) ions in the vicinity of structural P-OH groups. The Brønsted acidity of the latter may be enhanced by Brønsted-Lewis interaction, thus rendering catalysts with stronger acidity necessary for the skeletal isomerization. The lower molar fraction of Al(III) cations found in the ZnAPSO-11 solid, compared to the SAPO-11 sample, strongly supports the above. The results for the Zn-supported system were extremely different. Significant decreases in the strong acidity as well as in the skeletal isomerization selectivity, compared to the ZnAPSO-11 catalyst, were observed. These differences reinforce the idea of incorporation of Zn(II) into the silicoaluminate framework for the ZnAPSO-11 solid.