Mesoporous Alumina Research Articles

Reuse of secondary aluminum ash: Study on removal of fluoride from industrial wastewater by mesoporous alumina modified with citric acid

Longitudinal loading of citric acid as modifier onto the surface of other supports as highly efficient fluoride removing adsorbents has received extensive attention. But the loading of acid into mesoporous alumina synthesized using industrial solid waste secondary aluminum ash as raw material is rarely reported. In this study, MA was prepared by secondary aluminum ash reuse to industrial solid waste, and the MA was modified with citric acid for fluoride removal. The structural properties of this adsorbent were characterized by N 2 adsorption–desorption isotherm, XRD, FTIR spectroscopy. Meanwhile, the adsorption conditions, such as contact time, initial concentration and pH, were examined to evaluate the effect of fluoride adsorption. The adsorption properties are stable under acidic conditions. Chemisorption is a rate determining step because it complies with the Langmuir model and the pseudo second order model. The adsorption equilibrium was quickly reached in 30 min (117.98 mg g −1 ). With good cycling performance, 98.20% of the initial adsorption capacity was maintained after 5 cycles. Ion exchange between OH and fluoride is the main process of fluoride adsorption. The introduction of citric acid greatly increased the amount of -OH in the adsorbent. The extent of the influence of coexisting anions on fluoride adsorption is most pronounced for PO 4 3 − and CO 3 2 − . The results of high fluoride containing industrial wastewater treatment show that citric acid modified MA can solve the environmental pollution problem of industrial solid waste secondary aluminum ash on one hand, and at the same time provide new ideas for fluoride adsorbents. • Synthesizing mesoporous alumina with secondary aluminum ash for the first time. • Modification with citric acid increased hydroxyl radical on the surface of the material. • The removal efficiency remains above 98.20% after 5 cycles. • The maximum adsorption capacity for fluoride ions was 117.98 mg g −1 .

Heteropolyacid Incorporated Bifunctional Core-Shell Catalysts for Dimethyl Ether Synthesis from Carbon Dioxide/Syngas

Core-shell-type catalysts, which are synthesized by encapsulating the Cu-ZnO-Alumina type methanol synthesis catalyst (CZA) by silicotungstic acid (STA)-incorporated mesoporous alumina, were prepared following a hydrothermal route and tested in DME synthesis from syngas and CO2. Activity tests, which were performed in the pressure range of 30–50 bar, and the temperature range of 200–300 °C, with different feed compositions (CO2/CO/H2: 50/-/50, 40/10/50, 25/25/50, 10/40/50) showed that the best-operating conditions for the highest DME yield were 275 °C and 50 bar. Results proved that the presence of CO2 in the syngas had a positive effect on the DME yield. The total conversion of CO + CO2 increased with an increase in CO2/CO ratio. An overall conversion of CO + CO2 and DME selectivity values were obtained as 65.6% and 73.2%, respectively, with a feed composition of H2/CO2/CO = 50/40/10. Synthesis of methanol using the CZA catalyst from the CO2-containing gas mixtures was also investigated, and the total conversion of CO + CO2 and methanol selectivity values of 32.0% and 83.6%, respectively, were obtained with the H2/CO2/CO = 50/40/10 gas mixture. Results proved that the new STA incorporated core-shell-type bifunctional catalysts were highly promising for the conversion of CO2-containing syngas to DME.

Efficient toxic doxorubicin hydrochloride removal from aqueous solutions using facial alumina nanorods

A simple synthesis method was used for successfully preparing mesoporous alumina nanorods. The new mesoporous alumina nanorods were illustrated by several instrumentations such as XRD, SEM, and HRTEM. In addition, the surface area of the presented alumina was exhibited as 154.54 m2/g. The prepared alumina nanorods were found to have a wonderful ability for adsorbing the anti-cancer medication doxorubicin hydrochloride namely DOX. The mechanism of adsorption behavior of DOX was evaluated based on the variation of temperature, pH, and concentration of the DOX. Experimental data clarified that the adsorption capacity of alumina nanorods for DOX was higher at pH 6.0. The adsorption equilibrium also demonstrated that the Langmuir adsorption was regulated the best fit to the extracted data compared with the other models. The activation energy of adsorption was also measured for the adsorption of DOX onto alumina nanorods, which suggests the chemisorption movement. The adsorption kinetics was shown in the well-known kinetic model of the pseudo-second-order. The adsorption measurement was documented according to endothermic and spontaneous thermodynamic modules. The adsorption of DOX onto alumina nanorods from real water samples (tap water, effluent wastewater, and influence wastewater) were investigated. The results indicated that alumina nanorods were a good candidate for adsorbing the DOX and treating wastewater.

Synthesis and Characterization of Silica–Tantala Microporous Membranes for Gas Separations Fabricated Using Chemical Vapor Deposition

Composite membranes consisting of microporous tantalum-doped silica layers supported on mesoporous alumina substrates were fabricated using chemical vapor deposition (CVD) in both thermal decomposition and counter-flow oxidative deposition modes. Tetraethyl orthosilicate (TEOS) was used as the silica precursor and tantalum (V) ethoxide (TaEO) as the tantalum source. Amounts of TaEO from 0 mol% to 40 mol% were used in the CVD gas mixture and high H2 permeances above 10−7 mol m−2 s−1 Pa−1 were obtained for all conditions. Close examination was made of the H2/CH4 and O2/CH4 selectivities due to the potential use of these membranes in methane reforming or partial oxidation of methane applications. Increasing deposition temperature correlated with increasing H2/CH4 selectivity at the expense of O2/CH4 selectivity, suggesting a need to optimize membrane synthesis for a specific selectivity. Measured at 400 °C, the highest H2/CH4 selectivity of 530 resulted from thermal CVD at 650 °C, whereas the highest O2/CH4 selectivity of 6 resulted from thermal CVD at 600 °C. The analysis of the membranes attempted by elemental analysis, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy revealed that Ta was undetectable because of instrumental limitations. However, the physical properties of the membranes indicated that the Ta must have been present at least at dopant levels. It was found that the pore size of the resultant membranes increased from 0.35 nm for pure Si to 0.37 nm for a membrane prepared with 40 mol% Ta. Similarly, an increase in Ta in the feed resulted in an increase in O2/CH4 selectivity at the expense of H2/CH4 selectivity. Additionally, it resulted in a decrease in hydrothermal stability, with the membranes prepared with higher Ta suffering greater permeance and selectivity declines during 96 h of exposure to 16 mol% H2O in Ar at 650 °C.

Developing a Chromatographic 99mTc Generator Based on Mesoporous Alumina for Industrial Radiotracer Applications: A Potential New Generation Sorbent for Using Low-Specific-Activity 99Mo.

The commercial low-pressure column chromatographic 99Mo/99mTc generator represents a reliable source of onsite, ready-to-use 99mTc for industrial applications. These generators use fission-produced 99Mo of high specific activity, posing serious production challenges and raising proliferation concerns. Therefore, many concepts are aimed at using low-specific-activity (LSA) 99Mo. Nonetheless, the main roadblock is the low sorption capacity of the used alumina (Al2O3). This study investigates the feasibility of using commercial alumina incorporated with LSA 99Mo to develop a useful 99Mo/99mTc generator for industrial radiotracer applications. First, the adsorption profiles of some commercial alumina sorbents for LSA 99Mo were tested under different experimental conditions. Then, the potential materials to develop a 99Mo/99mTc generator were selected and evaluated regarding elution yield of 99mTc and purity. Among the sorbents investigated in this study, mesoporous alumina (SA-517747) presented a unique sorption-elution profile. It demonstrated a high equilibrium and dynamic sorption capacity of 148 ± 8 and 108 ± 6 mg Mo/g. Furthermore, 99mTc was eluted with high yield and adequate chemical, radiochemical, and radionuclidic purity. Therefore, this approach provides an efficient and cost-effective way to supply onsite 99mTc for radiotracer applications independent of fission-produced 99Mo technology.

Cobalt promoted molybdenum carbide supported on γ-alumina as an efficient catalyst for hydrodesulfurization of dibenzothiophene

The development of new hydrodesulfurization (HDS) catalysts with suitable electronic structure and metal-support interaction are critical for the efficient removal of sulfur from oil. In this work, cobalt-promoted molybdenum carbide supported on mesoporous alumina (CoxMo2C/MA) catalysts were prepared by a simple one-step hydrolysis method combined with a temperature programmed carbonization process, and the effects of Co on the physicochemical properties and HDS performance of the catalysts were systematically investigated. The results show that the appropriate Co addition can reduce the interaction between Mo species and alumina support, which is beneficial for the carbonization of Mo. Besides, the introduction of Co makes Mo species electron-rich, causing the C–S bond is vulnerable to attack. Taking dibenzothiophene (DBT) as a probe, Co0.3Mo2C/MA shows significant high sulfur removal efficiency (about 100%) and effective direct desulfurization selectivity. Furthermore, the density functional theory calculations further prove that the activation energy barrier of DBT HDS at the Co–Mo2C site is lower than that of Mo2C, confirming its reaction is easier to proceed. This work may provide a strategy for accessing new efficient modified molybdenum carbide catalysts for the HDS field.

Interactions of Ni/ZnO with alumina support and their influence on deep reactive adsorption desulfurization

Double hydrolysis mesoporous alumina (DHA) synthesized via hydrothermal technique and used as support for the loading of ZnO and Ni. The desulfurization activities and their interactions of Ni/ZnO/DHA adsorbents were compared with Ni/ZnO supported on commercially prepared alumina (Com). The higher breakthrough desulfurization activity and sulfur adsorption capability of these catalysts are influenced by the binding extant of Zn/Ni atoms with Al2O3 support, more free ZnO/Ni species and the formation of inactive ZnAl2O4 phases. The catalysts were characterized using nuclear magnetic resonance (NMR) spectroscopy, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, H2-temperature programmed reduction (H2-TPR) and N2 adsorption-desorption. Desulfurization activity shows that Ni/ZnO/DHA-80 °C catalyst achieved an excellent breakthrough sulfur removal (10 mg/L) up to 30.26 mL responsible for 110.4 mg S/g sulphur adsorption capability. This desulfurization performance is one fourth fold higher as compared to commercial Ni/ZnO/Com catalyst, achieving a compromised desulfurization activity of 1300 mg/L at set 30.26 mL model fuel flow with 38 mg S/g accumulative sulfur capacity. Detailed characterization results show that, the superior desulfurization activity shown by Ni/ZnO/DHA catalyst is due to the presence of meagre amount of unsaturated pentacoordinate Al3+ centers on Ni/ZnO/DHA surface which are responsible for lesser interaction of Ni/ZnO with Al2O4 and reduce the formation of inactive spinal ZnAl2O4 and NiAl2O4 phase even after many regeneration cycles which increases the active ZnO molar concentration as compared to Ni/ZnO/Com catalyst.

Production of carbon nanomaterials and syngas from biogas reforming and decomposition on one-pot mesoporous nickel alumina catalysts

Biogas, a renewable energy source, is primarily composed of CH4 and CO2. It is a promising alternative to fossil fuels and can be used directly for electricity production as well as heat generation via combustion. Concerns about climate change and a greater emphasis on renewable energy sources have recently increased interest in biogas utilization. In this context, biogas reforming and decomposition (BRD) into synthesis gas and carbon nanofibers (CNFs) is viewed as a new and attractive way of efficiently valorising biogas. In this study, Ni-loaded (i.e., 20, 50 wt%) mesoporous alumina materials were prepared using one-pot evaporation-induced self-assembly method for BRD. Synthesized materials were characterized by various techniques: N2-physisorption, X-ray diffraction, temperature-programmed reduction, scanning electron microscopy, and thermal gravimetric analysis. Results showed that textural and structural properties of synthesised materials differed with Ni loading. High Ni-loaded catalyst displayed higher surface area, pore volume, pore size distribution, and average particle size which is the result of deposition of Ni species outside alumina grains creating thus, surface defects. BRD results were greatly influenced by Ni content with Ni50%Al2O3 reflecting catalytic behaviour similar to those expected for pure methane decomposition. Most importantly, this catalyst was also capable of generating, selectively, interesting carbon nanofibers.

Strategy to Construct High Thermal‐Stability Narrow‐Band Green‐Emitting Si‐CDs@MAs Phosphor for Wide‐Color‐Gamut Backlight Displays

AbstractDeveloping innovative narrow‐band green‐emitting phosphors featuring low thermal quenching and eco‐friendliness for white light‐emitting diode (WLED) backlights is a pivotal challenge. Benefitting from narrowband and low toxicity of green‐emitting silanized carbon dots (Si‐CDs), an efficient confinement and protection strategy through embedding Si‐CDs in mesoporous aluminas (MAs) is proposed to construct MAs and Si‐CDs composites (Si‐CDs@MAs) with superior luminescence properties. Si‐CDs@MAs phosphor exhibits green emission at 526 nm with narrow full width at half maximum of 51 nm, zero‐thermal quenching even up to 423 K (104.1%@423 K of the emission peak intensity at 298 K), and the internal quantum efficiency of 64.46%. Compared with broad‐band yellow‐emitting solid‐state Si‐CDs (S‐Si‐CDs), the thermal stability, photostability, and water stability of Si‐CDs@MAs phosphor are remarkably improved due to surface protection. The WLED backlight is fabricated with optimized Si‐CDs@MAs phosphor, which shows high luminous efficacy of 117.43 lm W−1and wide color gamut (107% NTSC). Furthermore, this work provides the design principles of realizing stable narrow‐band solid‐state fluorescence carbon dots, suggesting its great potential for wide‐color‐gamut display application.

Tuning support acidity of Ni-based catalysts to improve hydrodeoxygenation activity for dibenzofuran

Controlling the oxygen-free product selectivity in catalytic hydrodeoxygenation is essential for producing high-quality fuel from coal- and biomass-derived liquids. In this paper, the selectivity of oxygen-free products and efficiency of hydrodeoxygenation of dibenzofuran as a model compound of coal- and biomass-derived liquids have been controlled by varying the Si content in the prepared catalysts (Ni/xSi-OMA, where x = SiO2/(SiO2 + Al2O3) and OMA = ordered mesoporous alumina). In comparison, the hydrodeoxygenation of dibenzofuran was performed using Ni/SBA-15, which displayed the lowest selectivity of oxygen-free products at 36.4%. On the other hand, doping Si in OMA introduces the Brønsted acid sites, which desirably enhances the selectivity of oxygen-free products. Above 99% selectivity of oxygen-free products has been attained for Ni/30Si-OMA and Ni/40Si-OMA catalysts. The Lewis acid sites of the OMA promote the deoxygenation efficiency through the enhanced adsorption of oxygen-containing intermediates. Besides, the Brønsted acid sites generated in OMA as the result of Si-doping promote the ring-opening and dehydration reactions of the oxygen-containing intermediates, which further lead to an overall enhanced hydrodeoxygenation performance for dibenzofuran.

Effect of textural characteristics on the catalytic performance of supported KCoMoS2 in the synthesis of higher alcohols from syngas

The influence of textural characteristics on the catalytic performance of supported KCoMoS2 catalysts was explored to provide essential information for the design of better catalysts for the synthesis of higher alcohols (C1–C5) from syngas. Syngas conversion was carried out over KCoMoS2 catalysts supported on various mesoporous (alumina and carbon-coated alumina) and microporous (two types of powdered activated carbons) materials. The experimental results show that catalysts supported over microporous materials exhibit higher catalytic activity in HAS from syngas than catalysts based on mesoporous materials.

High-performance Ni/OMA catalyst achieved by solid-state grinding – A case study of CO methanation

The development of methanation catalysts with a high catalytic activity at low temperatures and a long-term durability at high temperatures is still challenged by the conflicting constraint on the catalyst design. In this work, Ni(NO3)2·6H2O. and ordered mesoporous alumina (OMA) containing different amounts of the P123 template were co-ground to prepare Ni/OMA catalysts. Results indicate that NiO was embedded in the meso-channels of OMA via the solid-state grinding. Moreover, the metal particle size, dispersion and reducibility of the catalyst can be easily regulated by the amount of the residual P123 template in OMA, which can be simply controlled by changing the treatment temperature of the OMA precursor. The optimized 15Ni/OMA-120 with a high dispersion and small size of metallic Ni showed high low-temperature catalytic activity with TOF of 31.5 h−1 and STY of 319.1 molCH4 gcat h−1 at 340 °C, but also demonstrated good anti-sintering and coke-resistance performance with a time-on-stream of 150 h long-term durability at 600 °C, which is comparable with the counterpart 15Ni-OMA prepared by traditional wet-process of one-pot evaporation induced self-assembly.

Towards Highly Loaded and Finely Dispersed CuO Catalysts via ADP: Effect of the Alumina Support

To meet current economic demands enforcing the replacement of platinum-group metals, extensively used in three-way-catalytic converters (TWC), research is driven towards low-cost and widely available base metals. However, to cope with their lower activity, high metal loadings must be coupled with increased dispersion. Herein, a series of CuO/Al2O3 samples is produced and the effect of different alumina supports’ properties on CuO dispersion, speciation and eventually on the TWC performance is studied. The alumina samples are synthesized via different methods, including soft-templating routes and flame spray pyrolysis, and compared with a commercial one, while CuO used as the catalytic active phase is added through ammonia-driven deposition–precipitation. As found, the large surface area and low crystallinity of the aluminas produced by soft-templating routes favor strong metal–support interaction, generating highly dispersed and strongly bonded CuO species at low loading and copper-aluminate phases at high loading. Notably, the use of amorphous mesoporous alumina completely prevents the formation of crystalline CuO even at 15 wt% Cu. Such high metal loading and dispersion capacity without the application of elevated calcination temperatures is one of the best reported for nonreducible supports. Catalytic evaluation of this material reveals a pronounced enhancement of oxidation activity with metal loading increase.

Adsorption of Cd(II) on mesoporous Al2O3 prepared from high-aluminum fly ash

Cadmium (Cd) pollution has increased in water bodies due to an increase in industrial and agricultural activities, threatening human health and ecosystem stability. In this study, high-alumina fly ash (HAFA) was used as a low-cost raw material to prepare mesoporous alumina (MA) adsorbents to remove Cd(II) from water. The adsorption performance of the synthesized MA for Cd(II) was investigated at different pH values, initial Cd(II) concentrations, and contact times. The results showed that MA was successfully prepared from HAFA, and showed a specific surface area of 318.7 m2 g−1 and average pore size of 4.5 nm. The adsorption of Cd(II) on the synthesized MA had the best adsorption environment at pH 7, and the contact time to reach the dynamic adsorption equilibrium was 60 min. The pseudo-second-order and Langmuir models accurately described chemisorption and monolayer adsorption of Cd(II) on the surface of the synthesized MA, respectively. The fitting results of the Intra-particle diffusion model show that the intraparticle diffusion of particles is not the only step controlling the rate during the adsorption of Cd(II) by synthetic materials. The maximum adsorption capacity of the synthesized MA for Cd(II) was calculated to be 88.26 mg g−1 using the Langmuir isotherm.

Synthesis and Characterization of Mesoporous Aluminum Silicate and Its Adsorption for Pb (II) Ions and Methylene Blue in Aqueous Solution.

Aluminum silicate powder was prepared using two different syntheses: (1) co-precipitation and (2) two-step sol-gel method. All synthesized powders were characterized by various techniques including XRD, FE-SEM, FT-IR, BET, porosimeter, and zetasizer. The particle morphology of the synthesized aluminum silicate powder was greatly different depending on the synthesis. The synthesized aluminum silicate powder by co-precipitation had a low specific surface area (158 m2/g) and the particle appeared to have a sharp edge, as though in a glassy state. On the other hand, synthesized aluminum silicate powder by the two-step sol-gel method had a mesoporous structure and a large specific surface area (430 m2/g). The aluminum silicate powders as adsorbents were characterized for their adsorption behavior towards Pb (II) ions and methylene blue in an aqueous solution performed in a batch adsorption experiment. The maximum adsorption capacities of Pb (II) ions and methylene blue onto the two-step sol-gel method powder were over four-times and seven-times higher than that of the co-precipitation powder, respectively. These results show that the aluminum silicate powder synthesized with a two-step sol-gel method using ammonia can be a potential adsorbent for removing heavy metal ions and organic dyes from an aqueous solution.

A novel physisorption model based on mathematical morphology operators preserving exact pore morphology and connectivity

Complex large models of multi-scale microstructures of porous media do not exist in a manner adequately efficient to render their comprehensive analysis of textural and structural properties possible. The simulation of experimental processes, such as gas adsorption, raises two issues. First, the modeling of these complex materials must be sufficiently realistic. This implies that the numerical twin of the porous material must consider three essential aspects: a spatial structure defining different scales of porosity, comparable textural and structural properties of the real material and irregular pore morphology. Secondly, efficient algorithms must be developed to mimic the quasi-static phase transition behavior of fluids in a realistic manner. The proposed simulation approach allows to handle the physico-chemical phenomena inside complex materials by means of well-established mathematical operators. Morphological operators are used to efficiently mimic processes such as surface adsorption and pore filling. Fluid percolation that provokes phase transition is simulated by labeled connected components. This method relies entirely on morphological and structural operators, which has the advantage of substantially reducing the calculation time compared to that of density functional theory and molecular simulations-based approaches. In contrast to oversimplified models characterized by ideal pore shape and unconnected pores, our approach enables us to calculate the adsorption isotherm of realistic random models where pore morphology and porous network topology are unknown beforehand. We demonstrate that our model succeed in reproducing the adsorption isotherm of two well-known model materials (SBA-15 and KIT-5) and mesoporous alumina, represented by Cox Boolean models.

Mesoporous alumina-supported layered double hydroxides for efficient CO2 capture

A novel kind of CO2 solid adsorbents (xLDH/MA, x is the loading of LDH) was prepared by loading of layered double hydroxides (LDH) on the mesoporous alumina (MA) support. The LDHs in xLDH/MA were evenly distributed on the surface of MA. xLDH/MA possessed a large BET surface area (278–378 m2/g), narrow pore-size distribution (4.37–6.23 nm), and a highly crystalline framework. Among all of the samples, 30LDH/MA showed an excellent CO2 adsorption capacity at 50 °C (1.56 mmol/g), which was 1.55 times larger than that of unmodified MA. Due to the synergistic effect between MA and LDH, 30LDH/MA exhibited a higher surface area and a more amount of adsorption sites, which were the main factors improving its CO2 adsorption performance. The adsorption process of CO2 on xLDH/MA was dominated by the chemical adsorption, and the adsorbed CO2 was mainly stored in the form of carbonate. In addition, the 30LDH/MA composite material showed fast adsorption kinetics and good regeneration efficiency. We believe that such a kind of porous alumina-supported layered double hydroxides would have a great potential in the applications for the adsorption of CO2.

Easily synthesized mesoporous aluminum phosphate for the enhanced adsorption performance of U(VI) from aqueous solution

High-yield selective adsorbents and suitable modification methods are both significant for the efficient treatment of U-contaminated wastewater. In this work, a rich-mesoporous aluminum phosphate adsorbent (APO-10) was synthesized by simply increasing the mass of reactants under a fixed solvent volume. After increasing the mass of reactants ten times, APO-10 has the added defect level, the increased specific surface area, and mesoporous structure, and the increased number and enhanced adsorption ability of adsorption active sites (phosphorus-oxygen groups) on the surface, resulting in an enhanced adsorption performance of U(VI) in various environmental conditions. Its ultrahigh adsorption capacity calculated by the Langmuir model can reach 826.44 mg g−1 at pH = 5.5 and T = 298 K. Its crystal structure did not change after adsorption and remained at 584.40 mg g−1 after 6 cycles. Additionally, APO-10 shows an excellent uranium-selectivity over 68% from a mixed aqueous solution and has excellent applicability in the acidic and alkaline environment based on dynamic adsorption and desorption column experiments. This study not only provides a high-yield efficient selective adsorbent (APO-10) with excellent anti-radiation structure stability for the treatment of radioactive contamination but also provides a feasible modification method by simply increasing the mass of reactants.

Understanding the Diffusion Properties of Sulfur-Containing Compounds in Mesoporous Alumina: A Molecular Dynamics Study

Enhancing the diffusion of reactants in catalysts is imperatively needed in the hydrodesulfurization process. However, diffusion properties of sulfur-containing compounds are poorly characterized owing to experimental limitations. Herein, molecular dynamics (MD) simulation was applied to explore diffusion properties of thiane, thiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene in mesoporous alumina with pore sizes of 11.8, 13.6, and 15.3 nm. It is found that larger pore size and higher temperature facilitate diffusion. In other words, with the increase of pore size and temperature, the self-diffusion coefficient increased while the average interaction energy dropped. Notably, the diffusion activation energy showed that diffusion of larger molecules was more sensitive to variations in pore size and temperature. Furthermore, the effect of the molecular structure on diffusion was also studied; the increase in the number of benzene rings and branched chains was detrimental to diffusion. The simulated results were demonstrated by our experimental findings and harbor tremendous guiding significance for the design of effective hydrodesulfurization catalysts.

An attempt to tailor methane oxidation behaviors over Pd/Al2O3 systems through the concerted fashion of Zn and alkaline-metal promoters

Aiming to manipulate the properties of Pd/Al2O3 catalysts towards CH4 oxidation, trace of Zn and alkaline-earth metal (X = Mg, Ca, Sr and Ba) were dual-doped into mesoporous alumina. This was mainly inspired by their multi-functionality, in terms of the feature of semiconductor structure from amphoteric oxide ZnO, the higher metallicity and electron-donating effect from alkaline-earth metals, and the ability from both Zn and alkaline-earth metals to generate spinel phase with alumina. Eventually, the electron density throughout oxygen and metal atoms underwent rearrangement, the interfacial interaction and the surface work function of catalysts were altered. This in turn gave the distinction in the nanoparticle sizes and reducibility of palladium oxides, surface-concentration and stability of active PdO, distribution of surface oxygen species, and surface acid-base functionalities along the series of catalysts. Results demonstrated that the trade-off of these entire properties allowed Pd/ZnMg-MA with maximum light-off activity, whilst affording minimum drop in methane conversion over both Pd/ZnMg-MA and Pd/ZnBa-MA not only during long-term online test but also when water was injected into the feed.