Evaluation of the reactivity, selectivity and lifetime of hydrotalcite-based catalysts using isopropanol as probe molecule

Research on Chemical Intermediates https://doi.org/10.1007/s11164-021-04640-2 Evaluation of the reactivity, selectivity and lifetime of hydrotalcite‑based catalysts using isopropanol as probe molecule Zoulikha Abdelsadek1,2 · Sergio Gonzalez‑Cortes3 · Feroudja Bali2 · OuizaCherifi2 · Djamila Halliche2 · Patrick J. Masset4 Received: 6 September 2021 / Accepted: 15 December 2021 © The Author(s) 2022 Abstract Hydrotalcite catalysts derived from NiAl and NiAlMg mixed oxides were successfully prepared by coprecipitation at a constant pH of 11. Physicochemical methods were investigated to determine their structural and textural properties. Using isopropanol as a probe molecule, the acid–base properties of the catalysts were investigated, and the evaluation of reactivity, selectivity and lifetime was established. Keywords Hydrotalcite · Structural characterization · Isopropanol probe reactions · Acid–base properties Introduction Hydrotalcite is the generic name for isomorphic compounds of general formula Mg6Al2(OH)16 CO3·4H2O. Hydrotalcite-type anionic clays, layered double hydroxides (LDHs) containing exchangeable anions belong to materials that have attracted much attention in recent years. The structure of the layered double hydroxides can be visualized as the structure of brucite, Mg (OH)2. The brucite phase is constituted * Zoulikha Abdelsadek * Patrick J. Masset 1 Institute of Electrical and Electronics Engineering, University of M’hamed-Bougara, Independence Avenue, 35000 Boumerdès, Algeria 2 Laboratory of Chemistry and Natural Gas, Faculty of Chemistry, USTHB, El‑Alia, B.P. 32, 16111 Bab‑Ezzouar, Algiers, Algeria 3 Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK 4 Faculty of Mechanical Engineering, Koszalin University of Technology, ul. Śniadeckich 2, 75‑453 Koszalin, Poland 13 Vol.:(0123456789) Z. Abdelsadek et al. of octahedrons with six OH− groups each surrounded by Mg2+ ions. Sheets are then constituted by the replication of octahedrons. For derived hydrotalcite structures, a part of Mg+2 of the brucite is replaced by divalent and trivalent cations, where their atomic radius must be close to M g2+radius (r = 0.65 Å). The substitution leads to an excess of positive charges in the hydroxide layers, which are compensated by anions located in interlayer interspaces. The general chemical formula of LDHs is [M1−x2+Mx3+(OH)2]x+[An−]x/n.mH2O, with M2+ and M3+are divalent and trivalent metals, An−is an exchangeable interlayer anion such as CO32−, NO3−, Cl−…etc. and 3+ x is the molar fraction ratio M3+M+M2+ , respectively. The value of x is an important parameter to obtain a pure hydrotalcite structure with a good crystallinity. It has been reported that this is obtained only in the range 0.2 ≤ x ≤ 0.33. When x takes a value higher than 0.33, the gibbsite phase Al(OH)3 forms. Likewise, for low values of x, i.e., x < 0.2, the brucite phase Mg(OH)2 is stable [1, 2]. Different preparation methods of the hydrotalcites were investigated to tune their physical and chemical properties in order to apply them in specific applications. However, the coprecipitation process remains the best synthesis approach for the following reasons [3, 4]: • • • • • Easy and friendly condition method, Cost-effective, High reproducibility, High production rate and easily scalable, Good dispersion of the active phase. Several textural and structural properties of non-calcined and calcined hydrotalcite phases as nanomaterials have been applied in a wide variety of fields such as medicine, pharmaceutical, biotechnology, electronic, environment, catalysis and catalysts system (Fig. 1) [1]. Recently, oxides obtained by calcination of hydrotalcite have attracted much attention as catalytic system for applications, such as natural gas conversion and production of hydrogen by dry reforming of methane [5, 6], Friedel Craft reaction [7], methanol synthesis [8], etc. The calcination of hydrotalcites at sufficiently high temperatures leads to their dehydration, which is accompanied by de-hydroxylation and then decarboxylation reactions. It ends up with the collapse of the lamellar structure. In addition, mixed oxide phases are obtained at temperatures beyond 450 °C. The following properties can be highlighted from the combination of metal oxides [1, 6, 8–10]: • Stable phases with a significant specific surface (between 100 and 300 m2/g), • Tunable acidic/basic and redox properties, • Homogeneous dispersion of the active phase. The catalytic activity and selectivity of the catalyst are closely related to its acid–base, redox properties, textural and structural features resulting from the synthesis conditions. Several probe molecules like CO2 and NH3 were used to 13 Evaluation of the reactivity, selectivity and lifetime of… Fig. 1  Different applications of hydrotalcite characterize the basic and acidic properties of the solids surface, respectively. The conversion of alcohol as catalytic test reaction has been intensively investigated and used to characterize and evaluate the acid–base character of solid catalysts [11, 12]. Most of the attention has been paid to targeted molecules (e.g., isopropanol) that are transformed into products depending on the nature of the available reactive centers onto the heterogeneous catalyst surface. Such reactions have the advantage of being simple and easy to be followed through the quantification of conversion rates. In addition, it can be performed at relatively low temperatures. In contact with an acidic or basic solid, the isopropanol probe molecule may undergo mainly two types of competitive elimination reactions: (i) dehydration, which yields propylene and takes place on acid sites of the catalyst. The formation of di-isopropyl is also possible as a product of the dehydration of propylene and (ii) dehydrogenation reaction produces acetone and hydrogen and occurs in basic sites [13–15] (Fig. 2). The yield and selectivity of products for isopropanol transformation depend on the acid–base features of catalytic surface, which constitutes a well-suited probe molecule in the design of advanced catalysts. For each application, especially for catalysis applications, the acid–base properties of the catalysts are key parameters regarding their reactivity, selectivity and lifetime. There is strong incentive to enhance solid base properties of catalysts in order to improve their catalytic activity for reactions, such as alkylation, isomerization and Knoevenagel condensation reaction under specific friendly experimental conditions. Materials like zeolites, alkaline earth, basic resin, nickel ferrite spinel, oxides (ZnO, MgO), vanadium-containing catalysts and modified carbon have already been investigated for these reactions and isopropanol transformation [16–18]. Recently, there has been a great interest in the utilization of oxides obtained from calcined hydrotalcites due to their promising (...truncated)