Mechanochemical Route for Preparation of MFI-Type Zeolites Containing Highly Dispersed and Small Ce Species and Catalytic Application to Low-Temperature Oxidative Coupling of Methane

Abstract

MFI-type zeolites containing Ce species were prepared by a mechanochemically assisted two-step method, where first an amorphous Si–Ce–O composite was produced via a mechanochemical reaction of SiO2 and CeO2 and then transformed into an MFI-type zeolite under hydrothermal conditions. The Ce species in this sample were more highly dispersed than those in the two control materials: a Ce-containing MFI-type zeolite synthesized via the conventional one-pot hydrothermal approach and Ce species simply deposited on silicalite-1. The highly dispersed and small Ce species in the zeolite exhibited a unique catalytic performance for the oxidative conversion of methane after the impregnation of Pd species, and the combination of Pd and Ce species produced ethane even at reaction temperatures as low as 100–300 °C.

Improvement of Catalytic Activity of Ce-MFI-Supported Pd Catalysts for Low-Temperature Methane Oxidation by Creation of Concerted Active Sites

“…The detailed characterization results for the Si−Ce composite oxide, Ce-MFI MC , and Ce-MFI HT were provided in our previous report, 30 where the Ce species in Ce-MFI MC were confirmed by X-ray absorption spectroscopy and STEM-EDS measurements to be more highly dispersed than those in Ce-MFI HT . XRD patterns for Ce-MFI MC and 1Pd1M (M = Li, Mg, Fe, Co, Ni, Cu, Ru, Rh, Sm, Pt) are shown in Figure 1 (2θ range from 5°to 40°) and Figure S1 (2θ range from 5°to 80°).…”

“…The procedure used to synthesize Ce-MFI MC is the same as that described in our previous report. 30 For the preparation of the amorphous Si−Ce composite oxide, SiO 2 (3.6 g, Aerosil 200 V, Evonik Industries) and CeO 2 •nH 2 O (0.36 g, Fujifilm Wako Pure Chemical) were pulverized using a planetary ball mill (Pulverisette 7, Fritch) in a Si 3 N 4 pot with seven Si 3 N 4 balls (diameter 15 mm), where the revolution rate and total milling time were set to 600 rpm and 96 h, respectively. The ball milling was conducted by alternating between treatments and pauses for 15 min each to avoid overheating the sample and equipment.…”

“…Ce-MFI was also prepared by conventional hydrothermal synthesis as follows. 30 Ce(NO 3 ) 3 (Fujifilm Wako Pure Chemical) was dissolved in a mixture of TPAOH and NaCl aqueous solution (2.0 M, Fujifilm Wako Pure Chemical). Tetraethyl orthosilicate (TEOS, TCI) was then added to the solution.…”

“…The procedure was similar to that described in our previous report. 30 The Ce-MFI was dispersed in an ethanol solution containing each metal precursor: Pd(NO 3 ) 2 dissolved in 35 wt % HNO 3 aqueous solution,…”

“…Each product yield and methane conversion were calculated in the same manner as in our previous paper (see also the Supporting Information). 30…”