M(II)Al4 Type Layered Double Hydroxides—Preparation Using Mechanochemical Route, Structural Characterization and Catalytic Application

Abstract

The synthesis of the copper-poor and aluminum-rich layered double hydroxides (LDHs) of the CuAl4 type was optimized in detail in this work, by applying an intense mechanochemical treatment to activate the gibbsite starting reagent. The phase-pure forms of these LDHs were prepared for the first time; using copper nitrate and perchlorate salts during the syntheses turned out to be the key to avoiding the formation of copper hydroxide sideproducts. Based on the use of the optimized syntheses parameters, the preparation of layered triple and multiple hydroxides was also attempted using Ni(II), Co(II), Zn(II) and even Mg(II) ions. These studies let us identify the relative positions of the incorporating cations in the well-known selectivity series as Ni2+ >> Cu2+ >> Zn2+ > Co2+ >> Mg2+. The solids formed were characterized by using powder X-ray diffractometry, UV–Vis diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. The catalytic potential of the samples was investigated in carbon monoxide oxidation reactions at atmospheric pressure, supported by an in situ diffuse reflectance infrared spectroscopy probe. All solids proved to be active and the combination of the nickel and cobalt incorporation (which resulted in a NiCoAl8 layered triple hydroxide) brought outstanding benefits regarding low-temperature oxidation and increased carbon monoxide conversion values.

Synthesis of NiFe layered double hydroxides with varied layer charge densities: the templating effect of dioctyl sulfosuccinate

“…17,18 LDHs with x values smaller than 0.20 or larger than 0.33 have scarcely been reported. Examples are M 2+ Al-LDHs (M 2+ = Mg, Ni, Co, Zn, and Cu) with x > 0.33 [19][20][21][22][23][24][25][26] and MgAlcarbonate-, 10 -nitrate-, 27 -benzoate-, 28 -terephthalate-, 28 and -deoxycholate-LDHs, 29 MgGa-carbonate-LDH, 11,30 MgFe-chloride-, 31 and -carbonate-LDHs, 32 NiAl-carbonate-LDH, 33 and NiFe-carbonate-LDH with x < 0.20. 33 The study on the extended x has been limited and the successful preparation of a single phase LDH with x < 0.20 or x > 0.33 has not been reported so far.…”

Synthesis and Structure Refinement of [Co–Al4–X] LDHs (X = NO3– and SO42–) from Nordstrandite

“…The approximate formula is written as [Co 0.54 Al 2.4 (OH) 6 ]­(SO 4 ) 0.57 ·2.7H 2 O (Table ). This formula indicates a higher water content compared to other reported LDHs of this class. − …”

“…18 Szabados et al in a recent work report the synthesis of [Cu−Al 4 −X] LDHs (X = NO 3 − and ClO 4 − ) starting from gibbsite. 19 Britto and Kamath refined the structures of b-[Zn−Al 4 −X] (X = SO 4 2− and NO 3 − ) with a P12 1 /n 1 space group. 13 They also report a high chromate sorption capacity for b-[Zn−Al 4 − NO 3 ].…”

“…Szabados et al . in a recent work report the synthesis of [Cu–Al 4 –X] LDHs (X = NO 3 – and ClO 4 – ) starting from gibbsite …”

The magnetic properties of MAl4(OH)12SO4·3H2O with M = Co2+, Ni2+, and Cu2+determined by a combined experimental and computational approach

“…12, 13 and references cited therein) and recently their catalytic properties. 14 Our limited knowledge about their properties reflects the difficulty of obtaining phase pure samples; an issue only realized recently and solved by the combination of extensive synthesis optimization and detailed sample characterization by a suite of advanced characterization techniques. 12,13,15 The MAl 4 -LDH crystal structure (Fig.…”