Remarkable Effect of the Preparation Technique on the State of Cobalt Ions in BEA Zeolites Evidenced by FTIR Spectroscopy of Adsorbed CO and NO, TPR and XRD

Abstract

The state of cobalt in two BEA zeolites was studied by XRD, TPR, and FTIR spectroscopy using CO and NO as probe molecules. One of the samples, CoAlBEA (0.4 wt % of Co), was prepared by conventional ion exchange and the other, CoSiBEA (0.7 wt % Co), by a two-step postsynthesis method involving dealuminated SiBEA zeolite. The introduction of Co into SiBEA leads to an increase of unit cell parameters of the BEA structure and to the consumption of silanol groups in vacant T-sites of the dealuminated zeolite. In contrast, no structural changes are observed after incorporation of cobalt into AlBEA by ion-exchange. The reduction temperature of cobalt in CoSiBEA zeolite (1130 K), is much higher than for CoAlBEA and indicates a strong interaction of cobalt ions with SiBEA. Low-temperature CO adsorption on CoAlBEA results in (i) H-bonded CO, (ii) Co(3+)-CO adducts (2,208 cm(-1)) and (iii) a small amount of Co(2+)-CO complexes (2,188 cm(-1)). In agreement with these results, NO adsorption leads to the appearance of (i) NO(+) (2,133 cm(-1), formed with the participation of the zeolite acidic hydroxyls), (ii) Co(3+)-NO (1932 cm(-1)), and (iii) a small amount of Co(2+)(NO)(2) dinitrosyls (nu(s) = 1,898 and nu(as) = 1,814 cm(-1)). Low-temperature CO adsorption on CoSiBEA leads to formation of two kinds of Co(2+)-CO adducts (2,185 and 2,178 cm(-1)). No Co(3+) cations are detected. In line with these results, adsorption of NO reveals the existence of two kinds of Co(2+)(NO)(2) dinitrosyls (nu(s) = 1,888 and nu(as) = 1,808 cm(-1) and nu(s) = 1,878 and nu(as) = 1,799 cm(-1), respectively).

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.…”

FTIR Characterization of Fe3+–OH Groups in Fe–H–BEA Zeolite: Interaction with CO and NO

“…According to the literature [21][22][23][24], the band at 3744 cm -1 corresponds to external silanols, and that at 3737 cm -1 , to internal silanols. The broad feature at 3530 cm -1 corresponds to hydrogen-bonded SiOH groups located in hydroxyl nests or framework-defect sites [23].…”

“…The broad feature at 3530 cm -1 corresponds to hydrogen-bonded SiOH groups located in hydroxyl nests or framework-defect sites [23]. The band at 3608 cm -1 arises from the zeolite acidic Al-O(H)-Si hydroxyls [21][22][23][24]. Finally, the 3663 cm -1 band corresponds to Al-OH groups [21][22][23][24].…”

“…Interaction of CO with OH groups in zeolites is well documented [22,24,25]. Due to H-bonding, CO induces a broadening and a red shift of the OH bands.…”

The Reduction and Oxidation of Co Species in CoZSM-5 Zeolites Studied by IR Spectroscopy

“…It is known that C-O frequency decreases as the positive charge of cations increases due to stronger p-back donation of d-electrons from cations to CO p* antibonding orbitals. Hadjiivanow et al [18][19][20] reported the presence of a set of bands in the 2040-2140 cm -1 range assigned to carbonyl species of Co ? in reduced CoZSM-5.…”