Papers by Oluwole Ajumobi
Industrial & Engineering Chemistry Research
The use of solid adsorbents for CO 2 capture is of importance in the development of technologies ... more The use of solid adsorbents for CO 2 capture is of importance in the development of technologies to remove this greenhouse gas. High surface area mesoporous materials are used to encapsulate or functionalize amines that selectively capture CO 2. The MCM-41 class of hexagonally ordered mesoporous silicas have surface areas between 1000 and 1500 m 2 /g, which in principle allows a significant degree of capture when amines such as polyethyleneimine (PEI) are encapsulated within the pores and occupy the entire surface area of the materials. However, the tight 3 nm pore channels of MCM-41 create a challenge to the infiltration of PEI throughout the pore volume, resulting in much lower CO 2 uptake at high PEI concentrations. This work describes the introduction of clay nanotubes (halloysite) with an inner diameter of 15−30 nm into MCM-41 pellets to mitigate such diffusional restrictions. The introduction of the nanotubes is through a one-step ship-in-a-bottle approach to synthesis in an aerosolassisted system where MCM-41 is synthesized in droplets containing the halloysite. The morphology of the composite material is such that several nanotubes extend from the interior and protrude through the surface of the pellet like straws. These ceramic nanotubes are 0.5−2 μm in length, and their lumen diameter ranges from 15 to 30 nm, thus providing an improved entry pathway for molecules to access the interior of the MCM-41 pellets. The concept is used to enhance PEI loading in MCM-41, which leads to a significant increase in CO 2 uptake levels. MCM-41 composites with halloysite nano-straws (MCM-41/HNT) show a doubling of CO 2 uptake levels (7.1 wt %) and uptake kinetics (k = 0.11 s −1) in comparison to MCM-41 sorbents (3.9 wt % and k = 0.05 s −1) at 50 wt % PEI loading. This indicates the potential validity of the nano-straws to improve access to the interior of MCM-41, thus coupling enhanced molecular transport with a high surface area material. The generality of the concept indicates further applications to adsorption and catalysis.
Applied Catalysis A: General
Abstract ZSM-5 is a promising catalyst for the catalytic fast pyrolysis (CFP) of biomass due to i... more Abstract ZSM-5 is a promising catalyst for the catalytic fast pyrolysis (CFP) of biomass due to its high selectivity to light hydrocarbons. However, rapid deactivation of catalyst has been a major challenge towards the commercialization of CFP. The objective of our study is to evaluate the performance of MCM-41/ZSM-5 composites during the CFP of biomass. Here, for the first time, we report the synthesis of a unique MCM-41/ZSM-5 composite via a one-step, facile aerosol-based method. The composition of ZSM-5 in the composites was varied and the prepared composites were used as catalysts for the in-situ and ex-situ CFP of miscanthus × gigantus. The prepared composites were characterized by N2 adsorption-desorption, XRD, SEM, TEM and DRIFTS-pyridine adsorption. The results of CFP experiments demonstrated that ZSM-5 in the composites was fully accessible. Most importantly, MCM-41 acted as a sacrificial layer for coke deposition and decreased the deactivation rate of the ZSM-5.
Surfaces and Interfaces
Abstract This study described the synthesis of activated carbon and its application in the remova... more Abstract This study described the synthesis of activated carbon and its application in the removal of DBT and DMDBT from isooctane using both experimental and DFT calculations. The effect of synthesis conditions (pyrolysis temperature, precursor-activator ratio and ramping rate) on the properties of activated carbon were also presented. Activated carbon (AC) of high surface area and porosity was synthesized from an agricultural waste material (date seeds) using Zn-acetate as an activator. Thorough study of the characteristic activity and selectivity of this adsorbent in the removal of organosulfur compounds; dibenzothiophene (DBT) and dimethyldibenzothiophene (DMDBT) at room temperature were carried out. DFT simulations predicted the selectivity of AC towards DMDBT promoted by the charge donation and the positive inductive (+I) effects of the methyl groups resulting in strong van der Waals interactions and theoretical adsorption energy of – 12.3 kcal/mol. It was observed that surface area, porosity, and surface chemistry of the adsorbent highly depends on the process parameters. The adsorbent pyrolyzed at 1000 °C and 10 °C/min performs better and shows exceptional capability to remove DBT and DMDBT (200 ppmw-S) in model fuel to almost sulfur-free fuel at minimum adsorbent weight (200 mg). However, the precursor-activator ratios at optimum pyrolysis temperature and ramping rate had little effect on the adsorbents’ performance. DMDBT was found to preferentially adsorb on the adsorbents with increasing pore size and volume than DBT. The kinetics and isotherms studies confirmed that the obtained data fitted more to pseudo-second order and Langmuir model.
A facile aerosol-assisted technique was employed for the design of a new class of composite zeoli... more A facile aerosol-assisted technique was employed for the design of a new class of composite zeolite catalyst material with spherical morphology. This technique enables the one-step encapsulation of...
Solar Energy
Abstract In this work the synthesis of sulfur-doped cerium-titania based nanocomposites is carrie... more Abstract In this work the synthesis of sulfur-doped cerium-titania based nanocomposites is carried out for photoelectrochemical (PEC) water splitting applications. Pristine ceria (CeO2), titania (TiO2) and S-CeTiO4−x nanohybrid have been synthesized via facile hydrothermal technique. Additionally, sulfur doping is performed at 350 °C to achieve sulfidized-CeTiO4−x (S-CeTiO4−x) nanohybrid with improved optoelectronic properties. The energy disperse x-ray spectrometer (EDS) spectra and elemental mapping of S-CeTiO4−x showed the presence of sulfur. The X-Ray Photoelectron Spectroscopy (XPS) and X-ray diffraction (XRD) analysis further confirm sulfur doping and composite formation. Additionally, the XRD patterns of S-CeTiO4−x suggest the anatase phase of TiO2, which is slightly mitigated with sulfidation. The Brunauer–Emmett–Teller (BET) isotherms indicate the average pore size decreases from 20.82 nm to 18.35 nm after sulfidation, which confirms successful sulfur incorporation in the pores. The Kubelka-Munk plots acquired from UV/Vis-diffuse reflectance spectroscopy (DRS) displayed a substantial red shift in the bandgap with sulfidization from 3.00 eV to 2.50 eV. The photoelectrochemical (PEC) water splitting of S-CeTiO4−x photoanode in terms of photocurrent density suggesting more than 3-times increase as compared to pristine TiO2 nanoparticles. These results affirm the photoelctrocatalytic nature of ceria-based nanostructures for PEC water splitting.
Waste Management
A system of concentrated solar energy for pyrolysis of date palm waste to biochar is designed and... more A system of concentrated solar energy for pyrolysis of date palm waste to biochar is designed and simulated using SuperPro Designer v8.5. Both economic and environmental sustainability implications are evaluated by bench-marking with the conventional process (electric heating-based pyrolysis). Economic analysis shows that this process is more economically viable than the conventional process, with payback time (PBT) of 4 years and 132 days, internal rate of return (IRR) of 14.8%, return on investment (ROI) of 22.9% and gross margin of 35.5%. Environmental impact assessment shows that CO2 emissions from concentrated solar energy-based pyrolysis accounts for only 38% of that of the conventional pyrolysis, indicating that concentrated solar energy pyrolysis is more environmentally friendly. Sensitivity analysis shows that PBT is more sensitive to changes in biochar selling price than changes in the cost of acquiring date palm waste. This process presents sustainable opportunities for biochar production while reducing life cycle emissions and costs.
Arabian Journal for Science and Engineering
The worldwide increasing demand for environmentally-friendly transportation fuels and the strict ... more The worldwide increasing demand for environmentally-friendly transportation fuels and the strict regulations by the environmental protection agencies have put a great pressure on crude oil refining and upgrading industry. The main current technology for the desulfurization of crude oil and its fractions is hydrodesulfurization. However, this process is plagued with several drawbacks. The growing pressure on petroleum refining industries to reduce sulfur contents in fuels has made hydrodesulfurization process even more unappealing. Hence, more effective alternatives have been (and are still) sought by petroleum refining industries. Enzymatic desulfurization process has recently emerged as a promising alternative that has the potential to be cost-effective, efficient and environmental-friendly. In enzymatic desulfurization process, enzymes (whether intracellular or extracellular) attack organosulfur components in the crude oil or its fractions and remove sulfur through a series of enzymatic reactions. The process is an energy-saving process, devoid of emission of harmful gases into the atmosphere, and utilizes completely biodegradable catalysts. This article reviews the recent progress in desulfurization of crude oil and its fractions using extracellular and intracellular enzymes. Challenges encountered during enzymatic desulfurization are highlighted, and some potential solutions to tackle the challenges are proposed. Future outlooks into the development of more efficient enzymatic desulfurization processes have been pinpointed.
Energy & Fuels
The Ce–ZrO2 composite based catalysts were successfully synthesized using a hydrothermal synthesi... more The Ce–ZrO2 composite based catalysts were successfully synthesized using a hydrothermal synthesis technique. The Fe–Co metals were incorporated on the Ce–ZrO2 composite to enhance its catalytic performance during steam reforming of toluene. X-ray diffraction revealed the crystalline phases of the catalysts. The addition of Fe and Co improved the acidity (NH3-temperature programmed desorption) as well as the specific surface area (Brunauer–Emmett–Teller analysis) of the catalysts. The catalytic performance of the fluidized catalysts was evaluated under the realistic conditions in a CREC riser simulator at three different temperatures (600, 650, and 700 °C). The Fe–Co promoted Fe–Co/Ce–ZrO2 catalysts exhibited better performance for long-term operation in the steam reforming of toluene, while the Ce–ZrO2 composite catalyst stimulates CO2 reforming of methane. Moreover, Fe–Co/Ce–ZrO2 showed the highest H2 production (i.e., 63%) at 700 °C. Thus, Fe–Co/Ce–ZrO2 catalysts hold great promise in producing high-qu...
Applied Energy, May 15, 2018
Upgrading of oil sand bitumen by catalytic cracking of its heavy oil fraction via ceria-based cat... more Upgrading of oil sand bitumen by catalytic cracking of its heavy oil fraction via ceria-based catalysts was investigated in a fixed-bed flow-type reactor, in the presence of superheated steam and addition of water. The reaction was carried out over CeZr, FeCoCeZr1 and FeCoCeZr2 catalysts at 470 °C, Wcat/FFeed of 0.4 h and FH2O/Ffeed = 2. The oxygen species in the crystal lattice of the catalysts and the surface Lewis acid sites are responsible for the oxidative decomposition and catalytic cracking of the heavy oil, respectively. Higher light oil yield of approximately 60 mol%-C (gas oil and vacuum gas oil) and lowest coke yield (20.45 mol%-C) was obtained over CeZr catalyst. FeCoCeZr1 and FeCoCeZr2 gave lower residue and higher gas yield, with higher H2 and lower CO2 composition when compared to CeZr. The spent catalysts showed structural stability which is supported by the X-ray diffraction analysis, and thermal stability which agrees to the minimal weight loss from thermogravimetr...
Energy & Fuels
Series of nanosized iron- and cobalt-doped ceria–zirconia nanocomposites were prepared using a hy... more Series of nanosized iron- and cobalt-doped ceria–zirconia nanocomposites were prepared using a hydrothermal synthesis technique at 180 °C for 24 h, with the successful novel incorporation of both Co and Fe on ceria–zirconia, for n-hexane catalytic cracking. Effects of dopant ions on the improvement of intrinsic properties of ceria–zirconia nanocomposites were investigated using disparate characterization techniques. The synthesized ceria–zirconia nanocomposites exhibited similar X-ray diffraction (XRD) patterns, indicating full fusion of the metal ions into the ceria–zirconia lattice structure. The synthesized nanocomposite catalysts were tested for n-hexane cracking over 10 h time-on-stream, with no previous study or report for catalytic cracking of hexane via ceria–zirconia nanocomposites. Relatively high ethylene and propylene selectivity (both >62%) was obtained over CZ, FeCoCZa, and FeCoCZb over time-on-stream. Comparatively, the best catalytic activity and stability was exhibited by FeCoCZa with hig...
In many porous catalyst supports, the accessibility of interior catalytic sites to reactant speci... more In many porous catalyst supports, the accessibility of interior catalytic sites to reactant species could be restricted due to limitations of reactant transport through pores comparable to reactant dimensions. The interplay between reaction and diffusion in porous catalysts is defined through the Thiele modulus and the effectiveness factor, with diffusional restrictions leading to high Thiele moduli, reduced effectivess factors, and a reduction in the observed reaction rate. We demonstrate a method to integrate ceramic nanostraws into the interior of ordered mesoporous silica MCM-41 to mitigate diffusional restrictions. The nanostraws are the natural aluminosilicate tubular clay minerals known as halloysite. Such halloysite nanotubes (HNTs) have a lumen diameter of 15− 30 nm, which is significantly larger than the 2−4 nm pores of MCM-41, thus facilitating entry and egress of larger molecules to the interior of the pellet. The method of integrating HNT nanostraws into MCM-41 is through a ship-in-a-bottle approach of synthesizing MCM-41 in the confined volume of an aerosol droplet that contains HNT nanotubes. The concept is applied to a system in which microcrystallites of Ni@ZSM-5 are incorporated into MCM-41. Using the liquid phase reduction of nitrophenol as a model reaction catalyzed by Ni@ZSM-5, we show that the insertion of HNT nanostraws into this composite leads to a 50% increase in the effectiveness factor. The process of integrating nanostraws into MCM-41 through the aerosol-assisted approach is a one-step facile method that complements traditional catalyst preparation techniques. The facile and scalable synthesis technique toward the mitigation of diffusional restrictions has implications to catalysis and separation technologies.
Physico-chemical properties of AC were influenced with boron doping. Improved adsorption capacity... more Physico-chemical properties of AC were influenced with boron doping. Improved adsorption capacity was obtained at optimum 1 wt.% boron. Boron-doped AC adsorbent showed selectivity towards 4,6-DMDBT in the presence of naphthalene. Efficiency of the adsorbent was largely preserved after 5-cycles of regeneration. a b s t r a c t Activated carbon was modified with varying concentrations (0.5–10 wt.%) of boric acid to make adsor-bents with physico-chemical properties that are essential for the removal of bulky and recalcitrant 4,6-dimethyldibenzothiophene (4,6-DMDBT) from the model fuel via adsorptive desulfurization at room temperature. The features of boron-doped activated carbon adsorbents were examined in comparison with unmodified activated carbon using N 2 physisorption analysis, inductively coupled plasma-mass spectrometry, Raman spectroscopy, Fourier transform infra-red, temperature programmed desorption and scanning electron microscopy. Boron-doped adsorbents exhibited better adsorption capacity at low boron loadings of 0.5–2.5 wt.%, largely due to their preserved surface area compared to those with higher boron loadings (5–10 wt.%), and enhanced surface acidity, compared to the unmodified AC. Specifically, the adsorbent containing 1 wt.% of boron loading (1BDAC) gave the best adsorption performance of 85% (8.50 mg/g) in 100 ppmw-S containing 4,6-DMDBT within 5 min contact time. Furthermore, for the IBDAC sample, the effect of initial concentration, sorbent dosage, and selectivity were studied in the presence of naphthalene. Remarkable regeneration performance was exhibited by the 1BDAC adsorbent with only 7% loss in adsorption capacity after supplementary five-cycle regenera-tions. The kinetic studies showed that the adsorption followed a pseudo-second order model while iso-therm data were well fitted by Freundlich isotherm. With an optimum boron loading of 1 wt.%, the boron-doped AC showed selectivity towards complex refractory organosulfur compound (4,6-DMDBT), which highlights its efficacy for significantly removing the compounds from the model fuel.
Physico-chemical properties of AC were influenced with boron doping. Improved adsorption capacity... more Physico-chemical properties of AC were influenced with boron doping. Improved adsorption capacity was obtained at optimum 1 wt.% boron. Boron-doped AC adsorbent showed selectivity towards 4,6-DMDBT in the presence of naphthalene. Efficiency of the adsorbent was largely preserved after 5-cycles of regeneration. a b s t r a c t Activated carbon was modified with varying concentrations (0.5–10 wt.%) of boric acid to make adsor-bents with physico-chemical properties that are essential for the removal of bulky and recalcitrant 4,6-dimethyldibenzothiophene (4,6-DMDBT) from the model fuel via adsorptive desulfurization at room temperature. The features of boron-doped activated carbon adsorbents were examined in comparison with unmodified activated carbon using N 2 physisorption analysis, inductively coupled plasma-mass spectrometry, Raman spectroscopy, Fourier transform infra-red, temperature programmed desorption and scanning electron microscopy. Boron-doped adsorbents exhibited better adsorption capacity at low boron loadings of 0.5–2.5 wt.%, largely due to their preserved surface area compared to those with higher boron loadings (5–10 wt.%), and enhanced surface acidity, compared to the unmodified AC. Specifically, the adsorbent containing 1 wt.% of boron loading (1BDAC) gave the best adsorption performance of 85% (8.50 mg/g) in 100 ppmw-S containing 4,6-DMDBT within 5 min contact time. Furthermore, for the IBDAC sample, the effect of initial concentration, sorbent dosage, and selectivity were studied in the presence of naphthalene. Remarkable regeneration performance was exhibited by the 1BDAC adsorbent with only 7% loss in adsorption capacity after supplementary five-cycle regenera-tions. The kinetic studies showed that the adsorption followed a pseudo-second order model while iso-therm data were well fitted by Freundlich isotherm. With an optimum boron loading of 1 wt.%, the boron-doped AC showed selectivity towards complex refractory organosulfur compound (4,6-DMDBT), which highlights its efficacy for significantly removing the compounds from the model fuel.
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Papers by Oluwole Ajumobi