Understanding the Role of Rare Earths in Zeolite Y on the Removal of Sulfur from Hydrocarbon Fuels

Abstract

Adsorptive desulfurization is a promising alternative to hydrodesulfurization for minimizing harmful sulfur emissions from hydrocarbon fuels. Cu in Y zeolite (CuY) has shown effective sulfur adsorption, especially when paired with Ce (CuCeY). This study explores other rare earths (REs), including La, Sm, and Nd, in RE and CuRE Y and mesoporous Y (SAY) zeolites for the adsorption of benzothiophene (BT) and dibenzo­thiophene (DBT). Metal loadings on the zeolites were quantified by using inductively coupled plasma optic emission spectroscopy (ICP-EOS) and X-ray fluorescence (XRF). Characteristic adsorption modes, such as σ-bonding and π-complexation, were observed by using Fourier-transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) Rietveld refinement determined that RE ions prefer the sodalite cages of Y zeolite, while Cu occupies supercage sites. Ce showed the strongest synergy with Cu compared to the other REs and the highest adsorption capacity. The results of this study provide insight into the role of RE exchanged Y on sulfur adsorption.

In Situ XAFS, XRD, and DFT Characterization of the Sulfur Adsorption Sites on Cu and Ce Exchanged Y Zeolites

“…The metal ions were placed in the six-member rings of the zeolite including rings adjacent to the supercage and the sodalite cage, and the geometry was then optimized. Cu and Ce cations were placed within the zeolite structure according to our previous Rietveld refinement findings 36 and the known available active sites in Y zeolite. 83 A cut out of the Y unit cell is shown in Figure 3 with the positions of the cations and their local six-member rings highlighted.…”

“…After liquid ion exchange with HY, Ce has been reported in sites I′ and II′. 36 Recent work has shown the fabrication of Ce active sites for sulfur adsorption in the supercages of CeY materials. 37 This current study investigates the placement of Cu and Ce in Y zeolite to accurately characterize their structure as prepared for sulfur adsorption.…”

“…53,54 In bimetallic CuREY materials, the RE cations were located in the interior sites I′ and II′, while Cu was located in the supercage in site II. 36 The presence of metals in the supercage of the bimetallic Y zeolites has been suggested as a reason for their improved sulfur adsorption performance. Refinement of monometallic CuY and CeY did not show metal occupation of the supercage sites, corresponding to lower adsorption performance.…”

“…Refinement of monometallic CuY and CeY did not show metal occupation of the supercage sites, corresponding to lower adsorption performance. 36 To supplement experimental techniques, density functional theory (DFT) is a useful method for studying adsorptive materials. DFT calculations have been used to investigate the Cu sites in Y zeolites and examine their electronic properties.…”

Insight into the nature and the transformation of the hydroxyl species in the CeY zeolite

“…Rare earth (RE)-exchanged Y zeolites are the major active components of fluid catalytic cracking (FCC) catalysts and efficient adsorbents of selective adsorptive desulfurization (SADS) from liquid fuels. [1][2][3][4][5][6][7][8] The RE species in the zeolites have been found to play a vital role in the above areas. Such species have been found to be the efficient active sites to promote the adsorption and catalytic transformation of molecules.…”