Oyola Rivera, Oscar

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    Catalytic conversion of biomass renewable feedstocks to platform molecules using Brønsted acid catalysts
    (2018-05) Oyola Rivera, Oscar; Cardona Martínez, Nelson; College of Engineering; Hernández Maldonado, Arturo J.; Suárez, Oscar M.; Pagán Torres, Yomaira J.; Acevedo Rullán, Aldo; Department of Chemical Engineering; Abelleira Martínez, Oscar J.
    The fractionation of sugarcane bagasse, plantain peel and brewer’s spent grains to glucose, xylose and lignin was studied using 0.50 and 0.05 wt% H2SO4 as catalyst in a mixture of 80:20 wt% γ-valerolactone:water. We studied the production of glucose and xylose with up to 90, 94 and 88% cumulative yields for sugarcane bagasse, plantain peel and brewer’s spent grains, respectively. We studied the effects of the reaction conditions and physicochemical properties of the biomass wastes on the production of sugars from agriculture residues. The results showed that the reaction conditions affect the production of sugars and the effect may be different for each residue depending on its physicochemical properties. The lignin content, biomass crystallinity and ashes compositions are the physicochemical properties that most affect the production of sugars. The lignin can affect the accessibility to hemicellulose and cellulose during the reaction reducing the amount of sugars that can be obtained from biomass. The ashes present in the biomass may have alkaline species that can neutralize the acid catalyst reducing the rate of sugar production. The sugar production decreases as the biomass crystallinity increases. We show that the physicochemical properties of the sugar cane bagasse, plantain peel and brewer’s spent grains have a significant effect on its conversion to sugars. Also, we studied the production of levoglucosenone (LGO) via levoglucosan (LGA) and cellulose dehydration using Brønsted solid acid catalysts in tetrahydrofuran (THF). We evaluated the use of propylsulfonic acid functionalized SBA-15 (PS-SBA- 15), commercial acid functionalized SiO2 and zeolite catalysts for the dehydration of LGA. PS-SBA-15 showed the best catalytic performance to produce LGO from LGA. The highest LGO yield obtained from LGA using PS-SBA-15 was 58.6%. That yield is more than two times higher to that obtained using sulfuric acid, which was 24.5%. We showed that the conversion of cellulose to LGO using a solid acid catalyst must be assisted by a homogeneous acid catalyst such as sulfuric acid (H2SO4), to promote the depolymerization of cellulose into LGA. The main role of the solid Brønsted acid catalyst is the dehydration of LGA to LGO during the cellulose conversion to LGO. We identified that surface properties such as acid-surface interactions and hydrophobicity are important variables to explain the catalytic behavior of the solid acid catalysts evaluated. We also studied the stability of PS-SBA-15 in THF and 1.2 mM H2SO4 in THF. The physicochemical properties of the silica catalysts change for different treatment times in THF. However, these changes do not have a significant effect on the acidity and structure of the silica catalysts. On the other hand, adding H2SO4 to the THF causes a decrease in the acidity of the PS-SBA-15 after treatment. We demonstrated that solid Brønsted acid catalysts produce higher yields to produce LGO from LGA and cellulose than sulfuric acid. Also, we identified that the catalysts surface properties are a crucial parameter for the dehydration of LGA to LGO. Finally, we investigated the effect of Brønsted acidity on the production of dimethyl ether (DME) from carbon dioxide (CO2) using Pd-Ga2O3 catalysts supported on SiO2. A modification of a sol-gel method for the incorporation of Ga on the SiO2 surface was developed in order to improve the formation and dispersion of the Brønsted acid sites on the catalyst surface. The acidity analysis revealed that the Brønsted acid loading is higher on the catalyst synthesized using the sol-gel modified method. We observed that increasing the Brønsted acidity leads to an increase in the ratio of DME to methanol produced from CO2. We demonstrate a new simple method to improve the formation and the availability of Brønsted acid sites on Ga2O3/SiO2 catalyst surface using a modification of a sol-gel impregnation method. Also, the ratio of DME to methanol production is highly dependent of the Brønsted acidity loading on the catalysts surface.
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    Catalytic conversion of CO2 to hydrocarbons
    (2014) Oyola Rivera, Oscar; Cardona Martínez, Nelson; College of Engineering; Martínez Iñesta, María; Curet Arana, María; Acevedo Rullán, Aldo; Department of Chemical Engineering; Rivera Montalvo, Luis
    The production of methanol and dimethyl ether via CO2 hydrogenation was studied using Pd catalysts supported on α-Ga2O3, α-β-Ga2O3 and β-Ga2O3 polymorphs. The catalytic activity improves with the increase in the content of Pd2Ga intermetallic compound over the surface. The content of Pd2Ga over Pd/Ga2O3, reduced at 573 K, depends on the Ga2O3 crystalline phase present on the catalyst. A slight catalytic deactivation with time on stream was observed. The catalyst supported over α-β-Ga2O3 displayed the largest deactivation. The deactivation of the material appears to be the result of a loss of basic sites over the catalysts surface. The selectivity to dimethyl ether is not dependent on the Pd2Ga content, but depends on the catalyst acidity. The content of Pd2Ga over Pd/Ga2O3 catalysts was identified to be a crucial parameter for CO2 hydrogenation to methanol and dimethyl ether.