(550a) Investigating the Effect of Cu and Ce Loading in Mesoporous Y Zeolite for the Adsorptive Desulfurization of 4,6-Dimethyldibenzothiohene

Investigating the Effect
of Cu and Ce Loading in Mesoporous Y Zeolite for the Adsorptive Desulfurization
of 4.6-Dimethyldibenzothiohene

Kevin X. Lee, George
Tsilomelekis and Julia A. Valla

Department of Chemical
& Biomolecular Engineering, University of Connecticut, 191 Auditorium Road,
Unit 3222, Storrs, CT 06269-3222, USA,

Phone: +1-860-486 4602, e-mail: ioulia.valla@.uconn.edu

Sulfur emission from transportation fuels
can be detrimental, if they are not controlled. Conventional
hydrodesulfurization (HDS) has been the main process of sulfur removal
technology ever since it was founded. However, the recent aggressive use of
fossil-based fuel as energy source, particularly for the production of
transportation fuels, resulted in excessive energy consumption in the HDS
process. Adsorptive desulfurization using bimetal-exchanged mesoporous Y
zeolites has shown to exhibit high capacity and selectivity for thiophenic compounds
in liquid fuels¹. The combination of hierarchical
pore structure and ion-exchanged metal cations in the Y zeolite allows for
improved mass transfer of sulfur compounds to the active sites and stronger
bond formation via various adsorption modes, such as π-complexation and/or
σ-bond interaction ^2,3. Our recent studies have shown that
the synergy between two metal actions (e.g. Ce and Cu) plays a crucial role in
high adsorption selectivity and capacity of thiophene compounds, such as
thiophene, benzothiophene and dibenzothiophene ⁴. In this study we demonstrate that 2%Cu10%CeSAY
exhibited the highest 4,6-DMDBT capacity in the presence of aromatics,
producing up to 50 mL/g of clean fuel.

The experimental results were
strongly supported by characterization techniques and spectroscopic analysis. Metal-exchanged
mesoporous Y zeolites were first prepared by introducing mesoporosity via a
top-down surfactant-assistant technique.⁵ The mesoporous zeolite was subjected
to an ion-exchange procedure to replace the protons with either Cu or Ce
metals. The modified zeolites were characterized using various techniques. The
diffraction pattern and crystalline structure of each material were identified
using an x-ray diffractometer (XRD. The crystallinity and porosity, as well as
the presence of metal cations/nanoparticles were imaged using transmission
electron microscopy (TEM). Surface topographical analysis and surface elemental
mapping were performed by SEM with EDAX accessory. X-ray photoelectron
spectroscopy (XPS) experiments were conducted to provide quantitative and
oxidative information on the sample surface. The bulk metal loading in the
zeolite was calculated using an inductively coupled plasma equipped with a mass
spectrometer (ICP-MS). Subsequently, X-ray fluorescence (XRF) measurement was
acquired to analyze the bulk concentration of zeolite elements.

Breakthrough experiments were
conducted in a fixed-bed column to study the dynamic adsorption of model fuel (100
ppmw of DMDBT and 1% naphthalene in octane). The desulfurized effluent was
collected periodically until saturation had been reached and analyzed using a
gas-chromatograph-sulfur chemiluminescence detector (GC-SCD). Figure 1 shows
the breakthrough curves of DMDBT on various metal-exchanged mesoporous Y
zeolites with different metal loadings and order at which they were introduced.
Figure 1(a) confirms that Ce should be introduced first, followed by Cu in
mesoporous Y zeolite. Increasing the loading of Cu did not improve the
desulfurization performance, as indicated in Figure 1(b). In Figure 1(c), the
concentration of Ce was varied from 2 wt% to 10 wt%. All three zeolites
displayed higher adsorption of 4,6-DMDBT compared to 2%Cu2%CeSAY, as about 50
mL/g of clean fuel was produced. These results suggest that in combination with
the mesopores, the synergistic effects of Ce and Cu metals significantly
improve the capacity and selectivity of DMDBT.

Figure 1: Breakthrough curves of 100
ppmw of sulfur in DMDBT dissolved in n-octane on mesoporous Y zeolites
following the effects of a) metal configuration, b) Cu concentration, and c) Ce
concentration.

References

1.        Lee, K. X. & Valla, J.
A. Investigation of bifunctional zeolites for the adsorptive desulfurization of
fuels. Appl. Catal. B Environ. 201, 359–369 (2017).

2.        Yang, R. T.,
Hernández-Maldonado, A. J. & Yang, F. H. Desulfurization of transportation
fuels with zeolites under ambient conditions. Science 301, 79–81
(2003).

3.        Velu, S., Ma, X. &
Song, C. Selective Adsorption for Removing Sulfur from Jet Fuel over Zeolite-Based
Adsorbents. Ind. Eng. Chem. Res. 42, 5293–5304 (2003).

4.        Lee, K. X., Tsilomelekis,
G. & Valla, J. A. Removal of Benzothiophene and Dibenzothiophene from
Hydrocarbon Fuels using CuCe Mesoporous Y Zeolites in the Presence of
Aromatics. Appl. Catal. B Environ. (2018). In print.

5.        García-Martínez, J.,
Johnson, M., Valla, J., Li, K. & Ying, J. Y. Mesostructured zeolite Y—high
hydrothermal stability and superior FCC catalytic performance. Catal. Sci.
Technol. 2, 987 (2012).