Magnetic Fe3O4@SiO2–Pt and Fe3O4@SiO2–Pt@SiO2 Structures for HDN of Indole

Abstract

The effect of a second porous SiO2 shell in the activity and selectivity of the Fe3O4@SiO2–Pt catalyst in the hydrodenitrogenation of indole is reported. The double Fe3O4@SiO2–Pt@SiO2 structure was prepared by coating Fe3O4 nanoparticles with tetraethyl orthosilicate (TEOS) with a further impregnation of 1.0 wt.% of Pt on the (3-aminopropyl)triethoxysilane functionalized Fe3O4@SiO2 structures. The second porous SiO2 shell, obtained by using a hexadecyltrimethylammonium bromide (CTAB) template, covered the Fe3O4@SiO2–Pt catalyst with a well-defined and narrow pore-sized distribution. The full characterization by TEM, inductively coupled plasma-optical emission spectroscopy (ICP-OES), XRD, and N2 adsorption isotherm at 77 K and vibrating sample magnetometry (VSM) of the catalysts indicates homogeneous core@shell structures with a controlled nano-size of metallic Pt. A significant effect of the double SiO2 shell in the catalytic performance was demonstrated by both a higher activity to eliminate the nitrogen atom of the indole molecule present in model liquid fuel and the improvement of the catalytic stability reaching four consecutive reaction cycles with only a slight conversion level decrease.

Catalytic Hydrodenitrogenation of Pyridine under Hydrothermal Conditions: A Comprehensive Study

“…Although piperidine was not to be found in this experiment, most likely because conversion of piperidine happened quickly and piperidine was consumed completely within 5 min, the hydrogenation route from pyridine to piperidine was widely reported by other research studies. − Therefore, we reasonably treat piperidine as an intermediate product in the model. Considering that hydrogenation of the nitrogen heterocyclic ring substance is a reversible reaction, − dehydrogenation of piperidine is also included in this network (eqs and ). Piperidine disappearance is involved in the following reactions: 1-piperidineethanol formation via the reaction between piperidine and formic acid (eq ), generation of 1-carbaldehyde piperidine by substitution of H on the N atom in pyridine with formic acid (eq ), formation of other piperidines via the derivative reaction (eq ), and 1-pentanol formation after ring rupture of piperidine (eq ), which further combines with piperidine and leads to formation of 1-pentyl piperidine (eq ). Next, both 1-piperidineethanol and 1-carbaldehyde piperidine can further undergo hydrogenation to form 1-ethyl piperidine (eq ) and 1-methyl piperidine (eq ), respectively. Considering that the hydrogenolysis of short-chain amines, alcohols, and hydrocarbons could occur under supercritical water conditions, − we lump those minor amines, alcohols, hydrocarbons, and gas products together as NH 2 -R, HO-R, C n H m , and GP, respectively, in the network.…”

“…Generally, path 1r has a direct or an indirect strong impact on each compound, which suggests that dehydrogenation from piperidine to pyridine cannot be negligible. Indeed, for HDN of nitrogen heterocyclic ring chemicals such as indole, quinoline, carbazole, and so forth, dehydrogenation was an indispensable and essential step during the whole reactions. For pyridine, except for path 1 and path 1r, other paths have little impact on it.…”

DFT Insights into the Hydrodenitrogenation and Ring-Opening of Indole on an M (M = Ni, Pt, Ni–Pt) Slab Model

“…In order to improve the combustion value of indole, it is necessary to convert indole into alkanes by denitrification and ring opening reactions. Based on prior works [18][19][20], noble metal catalysts, such as Pt, are good for hydrogenation reactions, while the catalysts with an acidity function, such as Ni, are good for ring opening reactions. As mentioned above, it has been reported that Pt and Ni experimentally presented high catalytic activity for indole hydrodenitrogenation.…”