Continuous synthesis of doped layered double hydroxides in a meso-scale flow reactor

Abstract

Layered double hydroxides is a class of low cost structured nanomaterials with many potential applications in environmental catalysis and sustainable technologies. Their large scale use is hindered by the challenge of reproducible synthesis at scale. Here we report a general, readily scalable process for the reproducible synthesis of transition metal doped hydrotalcites using a two-step process: co-precipitation in a mm-scale (meso-scale) continuous flow reactor, followed by aging. We have shown that co-precipitation in flow at a residence time close to the micromixing time affords good control of particle formation. Reproducible synthesis allowed us, for the first time, to investigate the formation of the pore morphology of hydrotalcites and their thermal stability as a function of metal doping. The obtained samples exhibited surface areas (80-150 m 2 g-1) higher than those typically attained in batch syntheses, with very low standard deviation between the samples, a high degree of crystallinity and small crystallite sizes, in the range of 9.5-11.9 nm, depending on composition. A systematic characterization allowed us to elucidate the mechanism of the pore morphology formation: the crystallites were found to agglomerate into disk-like platelets, whereas the pore structure of the hydrotalcites is formed by agglomeration of the platelets.

Microwave‐Assisted Decarbonylation of Biomass‐Derived Aldehydes using Pd‐Doped Hydrotalcites

“…Pd‐HTs were synthesized by using a previously described mesoscale continuous‐flow method (Figure S1 in the Supporting Information), which yielded materials with reproducible elemental composition, surface area, and acid–base properties. Four Pd‐HT catalysts ( A , B , C , and D ) were synthesized with nominal loadings of 5, 1, 0.5, and 0.1 mol % Pd, respectively, by varying the metal precursor concentrations (Table S1 in the Supporting Information).…”

“…Therefore, HT‐supported catalysts could serve as a useful platform for stabilizing dispersed catalytic species on supports that have tunable electronic properties. Recently, we developed a highly reproducible synthesis route for the preparation of Pd‐functionalized hydrotalcites (Pd‐HTs) using coprecipitation under continuous flow . These Pd‐HTs had characteristics that were distinct from similar HT‐supported species obtained through post‐synthetic deposition .…”

Direct Conversion of Alcohols to Long-Chain Hydrocarbons via Tandem Dehydrogenation-Decarbonylative Olefination

“…The solution mixture was dropped into a beaker containing 100 mL of DI water with stirring (200 rpm), as previously reported. 3 The mixture was aged at 65 °C for 2 h, then cooled to room temperature, filtered and washed with DI water until the pH of the filtrate was neutral. The resulting powder was dried in air at 110 °C for 12 h and stored in a desiccator.…”

Acceptorless amine dehydrogenation and transamination using Pd-doped layered double hydroxides

“…Pd-free Mg-Al LDH (C) was also synthesized as a control via the same method. 35 Previously, our group had synthesized Pd-LDHs via two-step batch co-precipitation/wet deposition; however, the metal content of resulting materials was poorly reproducible, with standard deviations in the Pd, Mg, and Al molar ratios of up to 25 %. In contrast, the metal elemental composition of A, B, and C synthesized in flow are very reproducible, with standard deviations <5% of metal molar ratios (Table 1).…”