Copper-based layered double hydroxides (LDH) for the production of hydrogen and other value-added products

Author(s)

Rodrigo Morais Menezes dos Santos

• Document type: Doctoral Thesis
• Press: Araraquara. 2020-04-29.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
• Defense date: 2020-04-08
• Advisor: Celso Valentim Santilli

Abstract

Nowadays, the problems associated with the use of fossil fuels have been a topic of great concern, generating interest in processes based on the use of clean and renewable energy. Ethanol produced from renewable sources has proved to be advantageous in several aspects and promising in the replacement and/or complementation of the petrochemistry in the future, in obtaining several value-added products. Layered double hydroxides (LDH) and their derivatives have received much attention in the past decades due to important applications, particularly in catalysis, with advantages related to the uniform distribution of metallic cations in their structure, at the atomic level, in addition to the flexibility of compositions. Furthermore, when subjected to a thermal decomposition, LDH give rise to stable and highly dispersed metallic nanoparticles in a mixed oxide matrix, showing strong metal-support interaction. In this work, catalysts derived from CuZnAl-LDH containing 0, 5, 10 and 20% wt. copper were synthesized, evaluating their characteristics and their efficiency in the ethanol dehydrogenation reaction (EDR). The catalysts were analyzed by a set of techniques, with emphasis on the characterization by quick-XAS of the Cu and Zn species involved in the stages of formation of the catalyst and reaction under operando conditions. Through the use of chemometric tools, such as MCR-ALS in the treatment of datasets, it was observed that the copper content in the catalyst influences the phase composition in the support, providing different compositions of nano-ZnO, nano-ZnAl2O4 and an intermediate, identified as a tetrahedral pre-nucleus (TPN) of zinc. On the other hand, the support composition modifies the textural properties of the catalysts and, especially the nanoparticle sizes and dispersion of the active phase, related to the activity of the catalysts. Studying different activation routes, it was observed a greater activity related to a mixture of Cu+ :Cu0 species in relation to Cu0 species but with high instability of Cu+ species in conditions of greater conversions (at higher temperatures and copper contents). Additionally, the results show the importance of support in the dispersion of the active phase and stability, in which the use of LDH precursors showed interesting properties to be applied in a wide variety of catalytic reactions. (AU)

• FAPESP's process: 15/23410-5 - Copper-based layered double hydroxides for hydrogen production and other value-added products
• Grantee: Rodrigo Morais Menezes dos Santos
• Support Opportunities: Scholarships in Brazil - Doctorate