Method for Large-Scale Production of Multimetallic Layered Double Hydroxides: Formation Mechanism Discernment

摘要

A simple, economical, and environmentally friendly method for the production of layered double hydroxides (LDHs) is presented. The synthesis procedure is based on dispersing insoluble metal oxides, adjusting the pH by adding an optimum amount of metal nitrates, and dispersing and aging the product for a short time (6-8 h). The final product does not require washing, opposite to the traditional coprecipitation synthesis procedure. A dissolution-precipitation-recrystallization mechanism is proposed for the formation of LDHs, based on particle size measurements, XRD analyses, radial distribution functions, and ~(27)A1 MAS NMR studies. Solids were characterized by XRD, N2 physisorp-tion, TGA-DTA, SEM, and TEM, revealing that both LDHs and their calcination products have very similar properties to those prepared by conventional procedures. Pure LDH phase is obtained after 6- 8 h; a large, uniform particle size that would usually require prolonged hydrotherrrtal treatments is attained. Surface areas ranged from 32 to 93 m~2 g~(-1) and from 140 to 230 m~2 g~(-1) for fresh and calcined samples, respectively. This new method is intended to satisfy the growing demand of LDHs in large-scale applications as catalysts, SO_x adsorbents, PVC additives, etc.