Design of hybrid of nickel and carbon nanocatalysts and their applications on hydrogenation reactions

Author(s)

Bruno Henrique Arpini

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2022-08-29

Examining board members

Liane Marcia Rossi; Reinaldo Giudici; Janaina Fernandes Gomes

• Advisor: Liane Marcia Rossi

Abstract

Ni catalysts are widely used in hydrogenation reactions, including CO2 reduction, but this metal does not stand out for its selectivity. There are still many questions about the possible factors that control the selectivity of classical nickel catalysts in the hydrogenation of CO2 at atmospheric pressure, either to produce CH4 (Sabatier Reaction) or CO (Reverse Gas-Water Shift Reaction - RWGS). In this thesis, we developed a systematic study of the aging of nickel catalysts supported on silica (Ni/SiO2) under different atmospheres, and we managed to completely suppress the formation of CH4. This change was attributed to the formation of a species of Ni carbide (Ni3C), capable of desorbing CO much more easily compared to the free Ni surface. This improvement in selectivity for RWGS was observed when we performed the intentional coating of Ni with N-doped C (Ni@NC/SiO2). The catalyst managed to control the selectivity for CO, even with a larger average particle size, which, according to the state-of-the-art, should be better for the formation of CH4. This result is due to a weaker interaction of CO* on the surface of the coated catalyst when compared to the classical Ni catalyst. The Ni@NC/SiO2 catalyst also showed higher activity in the hydrogenation of alkynes when compared to the Ni/SiO2 and Ni Raney® catalysts. A complete Hammet correlation study and theoretical calculations showed that there may be a migration of hydrides generated on Ni surface to pyridine N-containing sites at 25 °C, or the possibility of a heterolytic cleavage of H2 on the Ni/C-N surface, to justify the higher activity found (AU)

• FAPESP's process: 17/24348-7 - Development of hybrid catalysts for conversion of CO2 into chemicals and fuels
• Grantee: Bruno Henrique Arpini
• Support Opportunities: Scholarships in Brazil - Doctorate