Influence of the Content and Environment of Chromium in CrSiBEA Zeolites on the Oxidative Dehydrogenation of Propane

Abstract

Cr x SiBEA catalysts (x ) 0.2, 1.0, and 3.4 Cr wt %) are prepared by a two-step postsynthesis method. The introduction of Cr ions in the framework of dealuminated SiBEA zeolite evidenced by XRD generates Brønsted acidic sites as shown by FTIR of pyridine used as molecular probe. In Cr x SiBEA as prepared, chromium is mainly present as octahedral Cr(III) and in calcined Cr x SiBEA (773 K, 3 h, flowing air) as distorted tetrahedral Cr(VI), as evidenced by DR UV-vis, TPR, and XPS. Upon outgassing of calcined Cr x SiBEA at 773 K for 1 h (10 -3 Pa), part of Cr(VI) is reduced to distorted tetrahedral Cr(V), as shown by EPR. Isolated distorted tetrahedral Cr sites present in activated Cr x SiBEA are responsible for their catalytic activity in the oxidative dehydrogenation (ODH) of propane, performed in the presence of air or N 2 O. The propane conversion increases with Cr content in the presence of air or N 2 O, while the selectivity toward propene depends on the reaction temperature and oxidant. In the presence of air, the selectivity toward propene is highest for 1.0 Cr wt %. The lower selectivity for the content of 3.4 Cr wt % may be the result of the presence of some amount of extra-framework octahedral Cr sites. The lower propane conversion and the higher selectivity toward propene in the presence of N 2 O probably depend on the oxidation state of Cr under reaction conditions and on the nature of surface oxygen. The presence of isolated tetrahedral chromium sites with oxidation state lower than (VI) on activated Cr x SiBEA is essential for maintaining a high selectivity.

One-pot conversion of furfural to useful bio-products in the presence of a Sn,Al-containing zeolite beta catalyst prepared via post-synthesis routes

“…The crystalline structure was preserved during the acid treatments, which is in agreement with the literature for HNO 3 -treated beta materials [83,[85][86][87][88][89]. The SSIE process did not lead to measurable changes in the crystalline structure of the materials deAl-betan.…”

Influence of preparation procedure on catalytic activity of PdBEA zeolites in aqueous phase hydrodechlorination of 1,1,2-trichloroethene

“…In the former case, a small shift from 2θ of 22.76° for HAlBEA to 2θ of 22.66° for PdHAlBEA is observed. These phenomena indicate the expansion of the matrix as a result of the reaction between Pd ions and OH groups of vacant T-atom sites (T = Si or Al) and Pd incorporation into BEA zeolite framework, as it was reported earlier[44,[46][47][48].…”

Cobalt Based Catalysts Supported on Two Kinds of Beta Zeolite for Application in Fischer-Tropsch Synthesis

“…Such high BE values of Co species were observed for CoBeta (782.6 eV) [36], washcoated CoFerrierite and Co 2+ -exchanged NaY (782.7-782.9 eV) [37,38] and for highly dispersed Co species in Co-ZSM-5 [39] (783.2 eV) with cobalt coordinated to lattice oxygen and probably incorporated into vacant T-atom sites [40]. It is well known that many metal cations located in zeolites also show higher BE comparing with their BE in oxides [41][42][43], which can be related to the degree of cations dispersion as well as the type of their interactions with the zeolite matrix in which they are incorporated.…”

“…(783.2 eV) with cobalt coordinated to lattice oxygen and probably incorporated into vacant T-atom sites [40]. It is well known that many metal cations located in zeolites also show higher BE comparing with their BE in oxides [41][42][43], which can be related to the degree of cations dispersion as well as the type of their interactions with the zeolite matrix in which they are incorporated.…”