SIPS 2018

DETAILLED PROGRAM OVERVIEW

Layered Double Hydroxides-based Materials as Catalysts for Sustainable Chemical Processes
Ioan-cezar Marcu¹;
¹LABORATORY OF CHEMICAL TECHNOLOGY & CATALYSIS, FACULTY OF CHEMISTRY, UNIVERSITY OF BUCHAREST, Bucharest, Romania;
PAPER: 169/AdvancedMaterials/Invited (Oral)
SCHEDULED: 11:20/Wed./Grego (50/3rd)

ABSTRACT:
Layered double hydroxides (LDH) belong to the anionic clays family, having the general formula M2+1-xM3+x(OH)2An-x/n·mH2O with a M2+/M3+ molar ratio between 1.5 and 4 [1]. M2+ and M3+ are bivalent (e.g., Mg2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) and trivalent (e.g., Al3+, Ga3+, In3+, Cr3+, Mn3+, Fe3+) cations, respectively, with ionic radii not too different from that of Mg2+ [2]. They are hexa-coordinated to hydroxyl groups, forming brucite-like sheets which stack to create a layered structure. A large variety of inorganic and organic counter-anions An- can be intercalated in the inter-layer space to compensate the positive charge introduced by the M3+ cations partially replacing M2+ cations in the layers. Two or more cations can simultaneously enter the brucite-like sheets, where they are homogeneously distributed and intimately mixed together. Due to their structure, along with their compositional flexibility, the LDH possess versatile physico-chemical properties which make them good candidates as multifunctional nanostructured catalysts and catalyst precursors [1, 3]. Various transition metals cations can be introduced into the layers of the LDH structure, but also into the inter-layer space as heteropolyanions and organometallic complexes where they are responsible for the redox properties of these materials and, therefore, for their catalytic properties in oxidation reactions. They can be used as such, particularly for low-temperature liquid-phase oxidation and epoxidation processes, or as mixed oxides obtained by their controlled thermal decomposition for high-temperature gas-phase selective oxidation, oxidative dehydrogenation, and total oxidation processes [4]. The thermal decomposition of the LDH leads to highly homogeneous mixed oxide structures with high specific surface areas, thermal stabilities, and tunable acid-base and redox properties. Due to these properties, the transition-metal-containing mixed oxides obtained from LDH precursors have been recognized as very promising catalysts for sustainable chemical processes, such as catalytic selective oxidation for obtaining chemicals and intermediates and complete oxidation as a promising valuable technology for the destruction of volatile organic compounds [4]. Through a number of examples selected mainly from our own research work, the high potential of transition-metal-containing LDH-based materials as catalysts for sustainable oxidation processes will be clearly demonstrated based on the correlation preparation method— physico-chemical characteristics— catalytic performance.

References:
[1] D. Tichit, B. Coq, CATTECH 7 (2003) 206-217.
[2] F. Cavani, F. Trifiró, A. Vaccari, Catal. Today 11 (1991) 173-301.
[3] G. Fan, F. Li, D. G. Evans, X. Duan, Chem. Soc. Rev. 43 (2014) 7040-7066.
[4] I. C. Marcu, A. Urdă, I. Popescu, V. Hulea, in Sustainable Nanosystems Development, Properties and Applications, M.V. Putz, M.C. Mirică (Eds.), IGI Global, Hershey, 2017, Ch. 3, p. 59-121.