Alkali-Free Zn–Al Layered Double Hydroxide Catalysts for Triglyceride Transesterification

Abstract

Zn-Al layered double hydroxides (LDHs) of general formula [Zn 2+ (1−x) Al 3+ x (OH) 2 ] x+ (CO 3 2− ) x/2 ·yH 2 O are promising solid base catalysts for the transesterification of lipids to biofuels. However, conventional synthetic routes employ alkali hydroxide/carbonate precipitants which may contaminate the final LDH catalyst and biofuel. The use of (NH 3 ) 2 CO 3 and NH 3 OH as precipitants affords alkali-free Zn-Al-LDHs spanning a wide composition range. The hydrothermal reconstruction of calcined Zn-Al-LDHs offers superior solid basicity and catalytic activity for the transesterification of C 4 -C 18 triglycerides with methanol, compared with cold liquid phase or vapour phase reconstruction. Hydrothermally activated Zn 3.3 -Al-LDH was stable towards leaching during transesterification. Abstract: Zn-Al layered double hydroxides (LDHs) of general formula [Zn 2+ (1x)Al 3+ x(OH)2] x+ (CO3 2− )x/2·yH2O are promising solid base catalysts for the transesterification of lipids to biofuels. However, conventional synthetic routes employ alkali hydroxide/carbonate precipitants which may contaminate the final LDH catalyst and biofuel. The use of (NH3)2CO3 and NH3OH as precipitants affords alkali-free Zn-Al-LDHs spanning a wide composition range. The hydrothermal reconstruction of calcined Zn-Al-LDHs offers superior solid basicity and catalytic activity for the transesterification of C4-C18 triglycerides with methanol, compared with cold liquid phase or vapour phase reconstruction. Hydrothermally activated Zn3.3-Al-LDH was stable towards leaching during transesterification.Scheme 1. Transesterification of triglyceride to biodiesel and glycerol by-product. Scheme 1. Transesterification of triglyceride to biodiesel and glycerol by-product.

Zn-Al Mixed Oxides Decorated with Potassium as Catalysts for HT-WGS: Preparation and Properties

“…The diffraction patterns for the ZnAl_X_K catalysts are presented in Figure 2. In the diffractograms of ZnAl_0.3_K and ZnAl_0.5_K, the characteristic bands for the cubic spinel structure ZnAl 2 O 4 with relatively high crystallinity were evidenced at 2θ: 31 [28,29]. Due to the structural similarity and similar diffraction images, it is justified to assign reflections for 2θ: 31.80 • , 36.10 • , and 56.56 • corresponding to diffraction on planes (100), (101), and (110), respectively, to the crystalline phase of wurtzite (ZnO) [30].…”

Synthesis and characterization of two-dimensional (2D) nanosheet zinc aluminum layered double hydroxide (Zn/Al LDH) via an alkali-free route

“…The diffraction peaks of the as-synthesis of the different molar ratios of Zn/Al LDH samples were characterized by XRD as shown in Figure 1. The diffraction patterns of the hexagonal unit cell of Zn/Al LDH were observed at 2 thetas, which are 15°, 21°, 26°, 32°, 39°, 42°, 65°, and 71°, corresponding to the plane of (003), (006), (009), (102), (105), (108), (110) and (113), respectively [4], [5]. The structure of the as-synthesis of the Zn/Al LDH sample was moderately crystalline nanostructure.…”

“…However, this method can harm the environment due to the emulsification and saponification process during the reaction, in the presence of an alkali substance, namely sodium hydroxide. It is notably known that sodium hydroxide would lead to leach because of sodium in the structure backbones [4]. To ensure the sustainability of the environment, an alkali-free method was introduced in this study.…”

“…An alkali-free method becomes more preferred in synthesis LDH because various metal group elements can be used [3]. Research on synthesis of Zn/Al LDH via this method, where zinc nitrate solution and aluminum nitrate solution are representing as a divalent cation (M II ) and a trivalent cation (M III ) respectively, are mixed with the addition of ammonium carbonate solution under constant pH [4], [5]. The mixing of both divalent and trivalent cations can cause the electrostatic interaction between the positive and negative interlayer because of the anion exchange capacity affected by the molar ratio [6].…”

Characterization and Efficacy of A Novel Formula of Insulin Chitosan Layered Duple Hydroxide-Nanohybrid for Oral Administration

“…Zn-Al LDH was prepared as mentioned previously [19]. Briefly, Zn (NO 3 ) 2 •6H 2 O and Al (NO 3 ) 3 •9H 2 O with a molar ratio 4:1 were dissolved in 100 mL distilled water, and NaOH (1 M) was added by dropwise until complete precipitation at pH (8)(9).…”