Palestra: HDO of model molecules derived from lignin catalyzed by molybdenum oxides: influence of the support and copper promoter

Resumo da Palestra: Bulk and supported molybdenum catalysts, in addition to the effect of copper as a promoter, were investigated on the activity, selectivity, and stability of molybdenum oxide in the hydrodeoxygenation of molecules derived from lignin. The catalytic performance was correlated with physicochemical properties using ICP-OES, XRD, XPS, Raman spectroscopy, N 2 physisorption, TPR, H 2 O-TPD, and oxygen chemisorption. The results showed that under the studied conditions, both the use of support and the addition of copper promoted the activity of molybdenum oxides, preserving the selectivity regardless of the tested molecule. The characterization studies showed that the species formed were mainly CuMoO 4 in bulk samples, MoO 3 , over titania and silica samples, and metallic copper, Cu 2 O, and MoO 2 , over activated carbon samples. The H 2 O-TPD and O 2 chemisorption results indicate that the inclusion of copper to molybdenum oxide promoted the reduction of molybdenum, the creation of oxygen vacancies, and the formation of H•, factors that favored the selective cleavage of the C–O bond. The hydrodeoxygenation of phenol promoted benzene formation (selectivity above 98%), indicating that the route followed was direct deoxygenation. Guaiacol was more reactive than anisole but had a lower rate of HDO due to a steric constraint. The distribution of products showed that the preferred route for anisole was demethylation, followed by deoxygenation, providing the formation of phenol and benzene. While for guaiacol, the main route was demethoxylation, providing phenol as the main product.

Palestra: From waste to value: CO2 conversion into liquid chemicals

Resumo da Palestra: The use of CO₂ as a carbon source, along with renewable H₂, to synthetize fuels and value-added chemicals is a promising route for mitigating CO₂ emissions via carbon capture and utilization (CCU) strategies. While CO₂hydrogenation is challenging, considerable progress has been made towards methanol (CH₃OH) synthesis, reaching a industrial level. CH₄ and CO are other molecules with one carbon (C1 products) that are concomitantly produced. Molecules with two or more carbons (C2+), such as hydrocarbons, olefins, and oxygenates, e.g. ethanol, possess high economic value and energy density than C1 products. They are versatile molecules with potential use as fuels and polymer precursors. Nevertheless, the C-C coupling reaction is difficult to control, and the reaction selectivity remains a daunting challenge when developing catalysts for C2+ synthesis. Another issue is how to minimize the formation of C1 products. The synthesis of C2+ products require the use of higher pressures (typically >20 bar). We have recently found that Ni catalysts with excellent selectivity toward CO at atmospheric pressure have the tendency to produce CH₄ when submitted to higher pressures, preventing the carbon chain growth. We have showed that the CO selectivity could be preserved at high pressure by designing a Ni₃ZnC catalyst phase. Later, we found that the in situ formation of the intermetallic nickel-zinc carbide phase also occurs when starting with Ni/ZnO, preserving the reaction selectivity towards the production of syngas at high pressures. The next step was the development of catalysts containing Fe, Cu, Co and K, following a similar approach to unlock the formation of C2+ products. The main results will be discussed in this talk.

Palestra: Effective synthesis of iron and vanadium nanocomposites with reduced graphene oxide for the photodecomposition of dyes

Resumo da Palestra: Water contamination is one of the major environment-related issues. It is associated not only with health problems, but with severe socioeconomic impacts, and synthetic dyes play a crucial role. Indigo carmine (IC) is an artificial vibrant blue dye, spread worldwide due to its use in denim making, but it is toxic, mutagenic, and very stable in nature. Among different techniques used to remediate dying wastewater pollution, heterogeneous photocatalysis of organic dyes emerges as a promising approach due to its advantages, such as catalyst recovery and reuse, use in mild conditions and pollutant chemical transformation. These reactions are considered advanced oxidative processes (AOPs). Nanocomposites of magnetite (Fe3O4) anchored on reduced graphene oxide (RGO) with different Fe3O4: RGO mass ratios and V 2 O 5 nanostructures with different morphologies as rods (B), massive microspheres (EM) and core- shell microspheres (CS), also anchored on RGO were synthesized, characterized and evaluated in indigo carmine (IC) photo Fenton discoloration. The Fe3O4:RGO nanocomposites presented high dispersion of iron oxide particles, at about 12nm on RGO surface sheets, though Fe3O4 high content related to RGO. The samples also showed bandgap energies below that found for bulk Fe3O4, showing an important effect of RGO. The complete IC discoloration was obtained after 30 min of reaction with Fe:RGO 17:1. XPS Fe2p3/2 showed that Fe3+/Fe2+ ratio was maintained even after three recycles (4 runs), meaning that RGO is responsible for stabilizing Fe3O4 particles, thus maintaining its photocatalytic activity. In the V 2 O 5 :RGO systems, V 2 O 5 - B/RGO showed the best performance probably due to the presence of V +4 (structural defects). Among the V 2 O 5 nanostructures, V 2 O 5 -B was the best and V 2 O 5 -CS the worst. After addition in RGO, the performance of the V 2 O 5 -B/RGO catalyst increased by 37% and the V 2 O 5 -CS/RGO increased by 48%. In this system, the pH of the reaction medium can increase the degree of reaction discoloration.

Palestra: Capture and Valorization of CO2: Opportunities in Homogeneous Catalysis with Metal Complexes

Resumo da Palestra: The rapid increase in atmospheric carbon dioxide (CO₂) levels and its detrimental effects on the environment have spurred a global drive to mitigate CO₂ emissions. One promising approach to address this challenge is the capture and valorization of CO₂ using homogeneous catalysis with metal complexes. By activating and transforming CO₂ into valuable products, this approach not only contributes to environmental sustainability by reducing greenhouse gas emissions but also offers economic opportunities by generating useful chemicals and materials. Homogeneous catalysis has paved the way for diverse and sustainable routes in the conversion of CO₂ into value-added products, encompassing processes such as hydrocarboxylation, hydrogenation, carbonylation, ammonium carbamate formation, carbonate synthesis, methanation, and catalytic transformation to methane. Among these, the transformative potential of photocatalysis shines prominently, as it leverages light-driven reactions mediated by transition metal complexes to orchestrate CO₂ reduction, unlocking a novel and environmentally conscious avenue for harnessing CO₂ as a valuable resource across industries. In this presentation, my main goal is to introduce the audience to the primary homogeneous photocatalytic systems used for CO₂ reduction, particularly in the generation of CO. By providing an overview of these essential processes, the intention is to spark an interest and curiosity among attendees, encouraging them to consider potential research endeavors in this field. Through this informative session, I aim to contribute to a deeper understanding of CO₂ valorization and its implications for a more sustainable future.