Silicate anion-stabilized layered magnesium–aluminium hydrotalcite

Preparation of an MCM‐22/Hydrotalcite Framework Composite and Its Catalytic Application

“…As‐synthesized HT shows reflections around 2 θ values of 12 and 23, corresponding to the (003) and (006) planes of the layered HT structure, respectively. The powder XRD pattern of pure MCM‐22 shows all reflections characteristic of the MWW (framework code of MCM‐22 zeolite) structure . The XRD profile of the as‐synthesized composite (MAMCM and MAMCM‐1), has reflections corresponding to the coexistence of both the layered HT structure and MCM‐22.…”

“…The 29 Si MAS NMR spectra of the composite materials show chemical shift values in the range –85 to –110 ppm, which is attributed to Si in different tetrahedral environments, such as Q 4 [Si(0M) 4 Si], Q 3 [Si(1M) 3 Si], and Q 2 [Si(2M) 2 Si], where M = Al, Mg, or H. The presence of the dominant Q 4 and Q 3 signals indicates the presence of Si in a condensed nature, similar to that in microporous materials , , . The observed broad signal indicates that framework silicate anions form as short‐range ordered structures and extra‐gallery silicate species, which is consistent with previously reported results , , . The observed NMR chemical shift values correspond to Si(OSi) x (OH) 4–2 x species, where x = 1 to 2, which indicate Si in layered‐type materials, as it is known to be in MCM‐22.…”

“…The MAMCM composite was prepared by a three‐step procedure. Initially the MCM‐22 and MA‐HT precursor gel were separately obtained as per procedures described in the literature , , . The MCM‐22 gel was prepared with a molar gel composition of SiO 2 /NaOH/Al 2 O 3 /HMI/H 2 O = 1:0.3:0.033:0.5:40 , .…”

“…In the second step, briefly, MA‐HT gel was prepared with a molar composition of Mg 2+ /Al 3+ /CO 3 2– /NH 4 + /H 2 O = 0.116:0.038:0.0769:0.379:30.6 . Solution 1 was prepared by dissolving metal nitrates of Mg and Al such as Mg(NO 3 ) 2 · 6H 2 O (29.74 g) and Al(NO 3 ) 3 · 9H 2 O (14.2 g), respectively, and solution 2 was prepared by dissolving bases such as (NH 4 ) 2 CO 3 (7.38 g) and NH 4 OH (13.28 g) in equal amounts of 30.6 m in deionized H 2 O (550.8 g).…”

“…In this regard, it is worth to mention here that recently, the introduction of silicate into the interlayer space of hydrotalcite materials was demonstrated. The resultant materials possess higher surface area and expose active sites favoring superior catalytic activity to that of traditional oxide catalysts derived from pure HT …”