Updated: Aug 21, 2020

In recent decades, highly efficient deep desulfurization processes have become very necessary to decrease environmental pollution due to sulfur emissions from fuels. Herein, an enhanced photocatalytic desulfurization of a model fuel was investigated under sunlight irradiation using H2O2 as the oxidant and Ag@AgBr loaded mesoporous silica Al-SBA-15 as a catalyst. In this study, the photocatalyst (Ag@AgBr/Al-SBA-15) was synthesized via a chemical deposition using halloysite clay as the silica-aluminum source and characterized by X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The UV-Vis DRS results revealed that the light absorption expanded to the visible region (λ > 400 nm) for the various Ag@AgBr nanoparticles doped in the mesoporous Al-SBA-15 material. The 30% Ag@AgBr/Al-SBA-15 sample with a 30% Ag@AgBr doping exhibited enhanced photocatalytic activity and showed high stability even after four successive cycles. The results demonstrated that initial dibenzothiophene (DBT) concentrations (500 ppm) reached 98.66% removal with 50 mg of the catalyst dosage, 1.0 mL of H2O2, for 360 min of sunlight irradiation at 70 °C.

Fig 1. (A) Small-angle and (B) wide-angle of XRD patterns of 10%-60%Ag@AgBr/Al-SBA-15 samples

Fig 2. (A) N2 adsorption-desorption isotherms, and (B) pore size distribution of Al-SBA-15 and 10%-60%Ag@AgBr/Al-SBA-15 samples. (C) Room temperature photoluminescence (PL) spectra of 10-60%Ag@AgBr/Al-SBA-15 samples

Fig 3. Photodegradation of DBT with different photocatalyst contents under sunlight irradiation at reaction temperatures of (A) 70 °C and (B) 50 °C. (Reaction conditions: Vmodel oil = 50 mL, mcatalyst = 50 mg, VH2O2 = 1.0 mL)

Fig 4. (A) Photodegradation of DBT by 30%Ag@AgBr/Al-SBA-15 catalyst at different temperatures under sunlight irradiation. (Reaction conditions: Vmodel oil = 50 mL, mcatalyst = 50 mg, VH2O2 = 1.0 mL). (B) Photodegradation of DBT by 30%Ag@AgBr/Al-SBA-15 catalyst at different amount of catalyst under sunlight irradiation. (Reaction conditions: Vmodel oil=50 mL, VH2O2=1.0 mL, reaction temperature of 70 °C)

Fig 5. Plot of (A) pseudo first-order and (B) pseudo second-order kinetic models for the degradation of DBT by photocatalytic oxidative desulfurization at different temperatures

This work was published in the Journal of Industrial and Engineering Chemistry

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Updated: Aug 21, 2020

Introducing additional meso- or macroporosity into traditionally microporous metal-organic frameworks (MOFs) is a very promising way to improve the catalytic performance of these materials, mostly due to the resultant reductions of diffusional barriers during reactions. Here we show that HKUST-1 can be successfully synthesised either via post-synthetic treatment (by acid-etching prepared HKUST-1 samples in phosphoric acid, referred to here as “HKUST AE”) or via in situ crystallisation (by exposing the MOF precursor solution to supercritical CO2, referred to here as “HKUST CO2”) to produce hierarchically porous structures that are highly beneficial for catalysis. These hierarchical MOFs were characterised by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and gas sorption to confirm the preservation of the microporous structure and the appearance of macropores in the crystallites. More importantly, the benefits of introducing a hierarchical porous structure into this MOF for improving the diffusion accessibility of reagents to the sample in catalysed liquid- and gas-phase reactions were quantified for the first time. It was found that the hierarchical pore structure helped to improve the catalytic performance in CO oxidation, which is evidenced by the greater extent of the reaction over HKUST CO2 compared to the commercial HKUST-1 sample over the same time period, at temperatures between 220 and 260 oC. The hierarchical porous structure proved even more beneficial in liquid phase reactions where more bulky molecules were involved; here the conversion of styrene oxide in methanolysis was used as an example. These findings serve to demonstrate the advantages of using such hierarchical porous MOFs in catalysis.

Figure. Results of CO oxidative reactions (a) and styrene oxide methanolysis reactions (b), showing an improvement in activity for the hierarchical porous MOF (red squares), compared to the normal microporous MOF (yellow triangles)

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Updated: Aug 21, 2020

In this report, we explore the use of supercritical CO2 (scCO2) in the synthesis of well-known metal-organic frameworks (MOFs) including Zn-MOF-74 and UiO-66, as well as on the preparation of [Cu24(OH-mBDC)24]n metal-organic polyhedra (MOPs) and two new MOF structures {[Zn2(L1)(DPE)]∙4H2O}n and {[Zn3(L1)3(4,4/-azopy)]∙7.5H2O}n, where BTC = benzene-1,3,5-tricarboxylate, BDC = benzene-1,4-dicarboxylate, L1 = 4-carboxy-phenylene-methyleneamino-4-benzoate, DPE = 1,2-di(4-pyridyl)ethylene, 4.4/-azopy = 4,4/- azopyridine, and compare the results versus traditional solvothermal preparations at low temperatures (i.e., 40 °Ϲ). The objective of the work was to see if the same or different products would result from the ssCO2 route versus the solvothermal method. We were interested to see which method produced the highest yield, the cleanest product and what types of morphology resulted. While there was no evidence of additional meso- or macroporosity in these MOFs/MOPs nor any significant improvements in product yields through the addition of scCO2 to these systems, it was shown that the use of scCO2 can have an effect on crystallinity, crystal size and morphology.

This work was published in the Special Issue Synthesis, Processing and Applications of Metal–Organic Frameworks using Compressed Fluids, Crystals 2020, 10(1), 17

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