Investigation of Cu(I)-Y zeolites with different Cu/Al ratios towards the ultra-deep adsorption desulfurization: Discrimination and role of the specific adsorption active sites

Abstract

Cu-containing materials attracted much attentions to adsorption desulfurization due to their excellent sulfur adsorption capacities. The chemical properties of adsorption active sites in the adsorbents and adsorption desulfurization mechanism, however, still remained ambiguous, which had impeded the development of a potential desulfurization adsorbent. This work aimed to address the aforementioned challenges by using Cu(I)-Y zeolites obtained via liquid phase ion exchange method. The implication of Cu/Al ratios on the chemical properties of active sites, the adsorption desulfurization performance and the mechanism was the major focus of this work. The desulfurization experimental results indicate that the remarkable sulfur breakthrough adsorption capacity (ca. 0.95 mmol S/g) can be achieved by the sample Cu(I)-Y-0.28, which is about ca. 2.0 folds as high as the best one reported. In this work, a new insight is put forward that except for the Brønsted acid sites and Cu+ species, the dimeric [Cu-O-Cu]2+ and [Cu-O2-Cu]2+ species located in the supercages of Cu(I)-Y adsorbents are identified and can be considered as the effective desulfurization active sites by employing in situ FTIR spectroscopy, IGA, XPS, and H2-TPR techniques. Furthermore, we also discover that the thiophene molecules can be independently adsorbed on the abovementioned adsorption active sites, rather than the thiophene oligomerization even if in the presence of Brønsted acid sites. DFT calculation further reveals the respective role of dimeric [Cu-O-Cu]2+ and [Cu-O2-Cu]2+ species for the thiophene capture, due to its different adsorption modes [(η1C) and (O-μ1-C, η1C, O-μ1-S)]. This study to distinguish effective adsorption active sites in the Cu(I)-Y zeolites should play an instructive role in the development of excellent desulfurization adsorbents in aspects of sulfur adsorption capacity and even adsorption selectivity.