Surface Basicity Research Articles

Continuous production of benzylideneacetophenone via gas phase reaction of benzaldehyde and acetophenone: Mechanism and reaction kinetics

Up to 10 times greater chalcone productivity vs. standard batch-liquid systems. • Continuous and time invariant acetophenone + benzaldehyde → chalcone over MgO. • Increase in chalcone production with specific surface basicity. • Undesired formation of benzyl alcohol and benzoic acid over SiO 2 and CeO 2. • Condensation mechanism described by Langmuir-Hinshelwood model. The continuous gas phase condensation of acetophenone (A) with benzaldehyde (B) into valuable (chalcone) benzylideneacetophenone ( P = 1 atm, 498 K ≤ T ≤ 573 K; E app = 58 ± 4 kJ mol −1 ) has been performed over an array of commercial oxides ( i.e. SiO 2 , ZnO, ZrO 2 , CeO 2 and MgO) with modified crystal size (18–50 nm, from XRD), specific surface area (8–176 m 2 g −1 ) and total surface basicity (based on carbon dioxide temperature programmed desorption (CO 2 -TPD)). Reaction operation under chemical controlled regime has been expressly established by parameter estimation and experimental variation of contact time and catalyst/reactant ratio. Full selectivity to target benzylideneacetophenone was achieved over ZnO, ZrO 2 and MgO, while benzaldehyde disproportionation to benzyl alcohol and benzoic acid (Cannizzaro reaction) was promoted using SiO 2 and CeO 2 . A direct correlation between activity and specific (per m 2 ) Lewis catalyst basicity has been presented, where MgO delivered the highest chalcone production rate. The reaction orders with respect to acetophenone and benzaldehyde have been estimated, while the experimentally determined benzylideneacetophenone production rates/ P A / P B profiles were subjected to a Langmuir-Hinshelwood type kinetic modelling. The best fit was obtained with a model involving non -competitive adsorption of A and B with the surface -C–C- bond formation as rate-determining. Our results demonstrate, for the first time, the sole formation of benzylideneacetophenone over extended reaction time (28 days on-stream) through an alternative continuous gas phase route involving acetophenone + benzaldehyde condensation using MgO to deliver an order of magnitude greater productivity relative to conventional batch liquid systems.

Cu supported Fe-SiO2 nanocomposites for reverse water gas shift reaction

This work analyses the catalytic activity displayed by Cu/SiO2, Cu-Fe/SiO2 and Cu/FSN (Fe-SiO2 nanocomposite) catalysts for the Reverse Water Gas Shift reaction. Compared to Cu/SiO2 catalyst, the presence of Fe resulted on higher CO’s selectivity and boosted resistances against the constitution of the deactivation carbonaceous species. Regarding the catalytic performance however, the extent of improvement attained through incorporation Fe species strongly relied on the catalysts’ configuration. At 30 L/gh and H2:CO2 ratios = 3, the performance of the catalysts’ series increased according to the sequence: Cu/SiO2 < Cu-Fe/SiO2 << Cu/FSN. The remarkable catalytic enhancements provided by Fe-SiO2 nanocomposites under different RWGS reaction atmospheres were associated to enhanced catalyst surface basicity’s and stronger Cu-support interactions. The catalytic promotion achieved by Fe-SiO2 nanocomposites argue an optimistic prospective for nanocomposite catalysts within future CO2-valorising technologies.

Effect of activation temperature on surface basicity of natural aluminosilicates

Montmorillonite and nontronite are layered aluminosilicates of smectite group minerals widely demanded in many industries owing to their unique physical-chemical and other properties. By thermal activation of raw clays there are variations in their porosity, surface area and physical-chemical properties, including formation and redistribution of surface active site of acid-base or redox character. The aim of present studies included investigation of the effect of thermal activation on the character of distribution and a number of basic sites on the surface of natural layered aluminosilicates by means of the new method of inverse thermoprogrammed desorption of СО2.&#x0D; Samples of natural aluminosilicates rich in montmorillonite (Montmorillonite 67%, illite 5%, quartz 5%, feldspars 21%) and nontronite (nontronite 70%, illite 10%, kaolinite 5%, quartz 10%, feldspars 8%) were characterized by XRD, XRF, BET N2 adsorption techniques. To probe surface basicity and determine the number of basic sites a new iTPD-CO2 was used. Prior the iTPD-CO2 measurement 100 mg of a sample was activated at 200, 300, 400oC, then cooled down and loaded with CO2 (3ml/min flow rate of CO2 for30 min). Next, the reactor was flushed by 5 ml/min N2-flow to desorb weakly sorbed CO2. The iTPD-CO2 profiles were recorded within 20-800oC at a 20oC/min heating rate and treated using ChemStation software.&#x0D; The experimental profiles of CO2 desorption for Mt and Nt samples observed two temperature regions. Low temperature peaks evolved around 80-90oC for Mt and between 110-127oC for Nt were most likely related to the weak basic sites, whereas high temperature peaks around 510 and 620oC for Mt and above 320oC for Nt testified to stronger ones. The reasoning of the obtained iTPD-profiles was done considering thermal behavior of layered aluminosilicates.&#x0D; The total basicity of Nt and Mt samples was 359.2 and 209.9 mmol/g respectively. The 1.6 times higher basicity of Nt was, obviously, caused by its phase and chemical composition and developed surface area and porosity. At higher activation temperatures the number of weak basic sites related to hydroxyl groups of adsorbed water molecules gradually decreased, namely, by 21 times for Mt and by 2.8 times for Nt.&#x0D; Dehydroxylation of structural Al-OH, Fe-OH, Mg-OH above 200oC, which becomes irreversible above 300oC, provided formation of residual oxygen atoms and their contribution to population of stronger basic sites. In accordance with thermal behavior of dioctahedral smectites, is assumed that strong basic sites of Mt are trans- and cis-vacant Al-OH groups dehydroxylating correspondingly at ~550 and 650oC. Fe-rich sample of Nt rapidly lost hydroxyls at rather lower temperatures that resulted in more heterogeneous distribution of strong basic sites of varying strength. At higher activation temperatures the ratio of stronger sites number to weak sites increased from 23 to 200 for Mt, whereas for Nt this ratio varied between 54-67 times. In general, total basicity of Mt and Nt decreased by 2.2-2.3 times as a result of their dehydration and dehydroxylation by thermal activation. The normalized values of basicity per unit surface area (BΣ/S, mmol/m2) were 1,5 times higher for Mt surface, testifying to higher occupancy and density of active sites for Mt than that of Nt.

Synthesis of high-specific-surface-area Li-Al mixed metal oxide: Through nanoseed-assisted growth of layered double hydroxide

Li-Al layered double hydroxide (LDH) and LDH-derived mixed metal oxide (MMO) are promising solid base catalysts due to their instinct and strong surface basicity. Herein, nano Li-Al LDH was synthesized via the crystal growth from metal hydroxide nanoseeds with low crystallinities. The present Li-Al LDH possesses high specific surface area (326 m2 g−1), highly crystalline, and high purity. The present nano LDH undergoes a transformation to Li-Al MMO with a high specific surface area (349 m2 g−1) of abundant strong basic sites. Indeed, the present Li-Al MMO exhibits an enhanced catalytic activity for a transesterification reaction between methanol and soybean oil compared to one prepared through a co-precipitation method, thanks to the larger amount of active sites.

Complexity of a Co3O4 System under Ambient-Pressure CO2 Methanation: Influence of Bulk and Surface Properties on the Catalytic Performance

Although using supported noble-metal catalysts for CO2 hydrogenation is an effective solution due to their excellent catalytic properties, metal oxide supports themselves can exhibit good activity being more economically feasible. This work focuses on investigating the complexity of the Co3O4 system during the CO2 methanation reaction, which is usually accompanied by the formation of unstable dispersions of cobalt oxide and metallic Co. Herein, we have tested different types of Co3O4: synthetically prepared mesoporous m-Co3O4 (BET surface area, 95 m2/g) and commercial c-Co3O4 (BET surface area, 15 m2/g; purchased from Merck) in the CO2 methanation reaction under different reduction temperatures (273–673 K). The reduction temperature was adjusted to 573 K for both the catalysts to reach the optimal Co/cobalt oxide ratio and consequently the best catalytic performance. m-Co3O4 is more active (CO2 conversion 95%) and stable at higher temperatures compared to c-Co3O4 (CO2 conversion 63%) due to its morphology-induced ∼66 times higher surface basicity. DRIFTS results showed differences in the detected surface species: formate was observed on m-Co3O4 and was proven to contribute to the total methane formation. It was revealed that in CO2 methanation reaction, both bulk and surface properties such as morphology, cobalt oxidation states, acid–base properties, and presence of defect sites directly affect the catalytic performance and reaction mechanism. Furthermore, 1% 5 nm Pt nanoparticles were loaded onto the Co3O4s to check the competitiveness of the catalysts. This study evidences on a cheap noble-metal-free catalyst for CO2 methanation consisting of m-Co3O4 with competitive activity and ∼100% CH4 selectivity.

Thermocatalytic CO2 Conversion over a Nickel-Loaded Ceria Nanostructured Catalyst: A NAP-XPS Study.

Despite the increasing economic incentives and environmental advantages associated to their substitution, carbon-rich fossil fuels are expected to remain as the dominant worldwide source of energy through at least the next two decades and perhaps later. Therefore, both the control and reduction of CO2 emissions have become environmental issues of major concern and big challenges for the international scientific community. Among the proposed strategies to achieve these goals, conversion of CO2 by its reduction into high added value products, such as methane or syngas, has been widely agreed to be the most attractive from the environmental and economic points of view. In the present work, thermocatalytic reduction of CO2 with H2 was studied over a nanostructured ceria-supported nickel catalyst. Ceria nanocubes were employed as support, while the nickel phase was supported by means a surfactant-free controlled chemical precipitation method. The resulting nanocatalyst was characterized in terms of its physicochemical properties, with special attention paid to both surface basicity and reducibility. The nanocatalyst was studied during CO2 reduction by means of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). Two different catalytic behaviors were observed depending on the reaction temperature. At low temperature, with both Ce and Ni in an oxidized state, CH4 formation was observed, whereas at high temperature above 500 °C, the reverse water gas shift reaction became dominant, with CO and H2O being the main products. NAP-XPS was revealed as a powerful tool to study the behavior of this nanostructured catalyst under reaction conditions.

Stable and Surface‐active Co Nanoparticles Formed from Cation (x) Promoted Au/x‐Co3O4 (x=Cs) as Selective Catalyst for [2+2+1] Cyclization Reactions

AbstractSurface‐active and highly stable cobalt nanoparticles generated from alkali ion‐promoted gold catalyst for catalyzed carbonylative [2+2+1] cyclization reaction, is described. The gold nanoparticle‘s (AuNPs) role was assumed to dissociate the CO and H2 into atomic species on the catalyst surface by spillover, which in‐situ reduces the robust mesoporous cobalt oxide to metallic cobalt (Co3+→Co2+→Co), as the active catalytic species that catalyzed the reaction; thereby providing up to 93 % yield of cyclopentenone adducts. Prior to this, catalyst pre‐treatment with H2 gas (130 °C, 3 h, 20 atm) was performed to reduce the catalyst. It appeared that the low reducibility temperature and increased surface basicity ascribed to the presence of alkali ion‐promoters in the catalyst revealed a strong correlation with the catalyst activity, for the intra‐ and intermolecular reactions under milder reaction conditions. Thus, a sustainable, highly reusable, and environmentally friendly green catalyst for the carbonylation reaction, such as Pauson‐Khand, was developed.

A comparative study on the catalytic performances of alkali metals-loaded KAlSiO4 for biodiesel production from sesame oil

Orthorhombic phase KAlSiO4 and the alkali metals-impregnated samples were examined as the heterogeneous catalysts for transesterification of sesame oil to biodiesel. According to the structural and compositional characterization using XRD, FT-IR and EDX techniques, the products had the aluminosilicate frameworks containing a random network of tetrahedral Al and Si units charge-balanced with alkali metal ions that could act as the strongly basic active sites. The BET, SEM, and TEM analyses, and surface basicity determination indicated that the as-made microstructures were of type II, typical of mesoporous materials which supply many sites for fully contacting of triglyceride and methanol to develop their catalytic activity. The performances of catalysts for the transesterification of sesame oil were investigated and compared under optimum conditions: carbonate loading of 50 wt%; methanol to sesame oil molar ratio, 6:1; catalyst amount of 5 wt% (relative to the weight of sesame oil); reaction temperature, 75 °C and reaction time, 3 h. The composition of FAMEs was also successfully determined using gas chromatography–mass spectrometry (GC–MS) where peaks corresponded to fatty acid methyl esters of sesame oil. The results demonstrated that the catalytic activity of KAlSiO4 was remarkably increased, 21.6%–97.6%, with alkali metal impregnation method in the order of Li > K > Rb > Na > Cs. It seems that the small size of lithium ion causes its excellent interaction with KAlSiO4, more easily insertion in the framework and good dispersion on the support surface resulted in reasonably high activity in transesterification reaction.

Improving Product Yield in the Direct Carboxylation of Glycerol with CO2 through the Tailored Selection of Dehydrating Agents

Improved yields of, and selectivities to, value-added products synthesised from glycerol are shown to be achieved through the judicious selection of dehydrating agents and through the development of improved catalysts. The direct carboxylation of glycerol with CO2 over lanthanum-based catalysts can yield glycerol carbonate in the presence of basic species, or acetins in the presence of acidic molecules. The formation of glycerol carbonate is thermodynamically limited; removal of produced water shifts the chemical equilibrium to the product side. Acetonitrile, benzonitrile and adiponitrile have been investigated as basic dehydrating agents to promote glycerol carbonate synthesis. In parallel, acetic anhydride has been studied as an acidic dehydrating agent to promote acetin formation. Alongside this, the influence of the catalyst synthesis method has been investigated allowing links between the physicochemical properties of the catalyst and catalytic performance to be determined. The use of acetonitrile and La catalysts allows the results for the novel dehydrating agents to be benchmarked against literature data. Notably, adiponitrile exhibits significantly enhanced performance over other dehydrating agents, e.g., achieving a 5-fold increase in glycerol carbonate yield with respect to acetonitrile. This is in part ascribed to the fact that each molecule of adiponitrile has two nitrile functionalities to promote the reactive removal of water. In addition, mechanistic insights show that adiponitrile results in reduced by-product formation. Considering by-product formation, 4-hydroxymethyl(oxazolidin)-2-one (4-HMO) has, for the first time, been observed in all reaction systems using cyanated species. Studies investigating the influence of the catalyst synthesis route show a complex relationship between surface basicity, surface area, crystallite phase and reactivity. These results suggest alternative strategies to maximise the yield of desirable products from glycerol through tailoring the reaction chemistry and by-product formation via an appropriate choice of dehydrating agents and co-reagents.

Green and selective hydrogenation of aromatic diamines over the nanosheet Ru/g-C3N4-H2 catalyst prepared by ultrasonic assisted impregnation-deposition method

In this study, nanosheet g-C3N4-H2 was prepared by thermal exfoliation of bulk g-C3N4 under hydrogen. A series of Ru/g-C3N4-H2 catalysts with Ru species supported on the nanosheet g-C3N4-H2 were synthesized via ultrasonic assisted impregnation-deposition method. Ultrafine Ru nanoparticles (<2 nm) were highly dispersed on nanosheet g-C3N4-H2. Strong interaction due to Ru-Nx coordination facilitated the uniform distribution of Ru species. Meanwhile, the involvement of surface basicity derived from abundant nitrogen sites was favourable for enhancing the selective hydrogenation performance of bi-benzene ring, i.e., almost complete 4,4′-diaminodiphenylmethane (MDA) conversion and >99% 4,4′-diaminodicyclohexylmethane selectivity, corresponding to a reaction activity of 35.7 molMDA molRu−1 h−1. Moreover, the reaction activity of catalyst in the fifth run was 36.5 molMDA molRu−1 h−1, which was comparable with that of the fresh one. The computational results showed that g-C3N4 as support was favorable for adsorption and dissociation of H2 molecules. Moreover, the substrate scope can be successfully expanded to a variety of other aromatic diamines. Therefore, this work provides an efficient and green catalyst system for selective hydrogenation of aromatic diamines.

Heat treatment effect on nanostructured sol-gel derived lanthania doped with chromium

Chromium doped lanthanum oxide synthesized by glycerol-assisted sol-gel route was heat treated at different temperatures up to 860 °C in order to investigate the effect of treatment temperature on the atomic environment in these samples. The addition of Cr2O3 to La2O3 catalyst support and catalytic promoter was considered because chromium is an interesting catalyst dopant.As the temperature rises from 100 to 860 °C, nanostructured La(OH)CO3, La2O2CO3 and La(OH)3 phases are developed in the treated samples. The crystallites size increases with treatment temperature from about 10 nm up to 30 nm, and at the same time a higher surface basicity is obtained, that would imply an enhanced catalytic activity or an improved behavior as catalyst substrate. The La2O2CO3 stable phase against moisture was obtained by relative low temperature synthesis. The tendency to atmospheric CO2 adsorption was evidenced for La(OH)3 phase developed in the samples treated at 650 and 860 °C.The X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses were used to evidence structural changes with influence on sample properties.

Catalytic conversion of ethanol to butanol over magnesium oxide catalysts

Several types of magnesium oxide (MgO) has been studied as catalyst for catalytic conversion of ethanol into butanol. The reactions have been conducted at 350 °C in batch reactor. MgO catalysts have been characterized by XRD, CO2-TPD, and N2-physisorption. It was found that of the highest yield of butanol was obtained from MgO synthesized from precipitation method. The highest butanol yield was 2.4% at our experimental conditions. This was attributed to its surface area and basicity.

Continuous selective deoxygenation of palm oil for renewable diesel production over Ni catalysts supported on Al2O3 and La2O3-Al2O3.

The present study provides, for the first time in the literature, a comparative assessment of the catalytic performance of Ni catalysts supported on γ-Al2O3 and γ-Al2O3 modified with La2O3, in a continuous flow trickle bed reactor, for the selective deoxygenation of palm oil. The catalysts were prepared via the wet impregnation method and were characterized, after calcination and/or reduction, by N2 adsorption/desorption, XRD, NH3-TPD, CO2-TPD, H2-TPR, H2-TPD, XPS and TEM, and after the time-on-stream tests, by TGA, TPO, Raman and TEM. Catalytic experiments were performed between 300–400 °C, at a constant pressure (30 bar) and different LHSV (1.2–3.6 h−1). The results show that the incorporation of La2O3 in the Al2O3 support increased the Ni surface atomic concentration (XPS), affected the nature and abundance of surface basicity (CO2-TPD), and despite leading to a drop in surface acidity (NH3-TPD), the Ni/LaAl catalyst presented a larger population of medium-strength acid sites. These characteristics helped promote the SDO process and prevented extended cracking and the formation of coke. Thus, higher triglyceride conversions and n-C15 to n-C18 hydrocarbon yields were achieved with the Ni/LaAl at lower reaction temperatures. Moreover, the Ni/LaAl catalyst was considerably more stable during 20 h of time-on-stream. Examination of the spent catalysts revealed that both carbon deposition and degree of graphitization of the surface coke, as well as, the extent of sintering were lower on the Ni/LaAl catalyst, explaining its excellent performance during time-on-stream.

A high performance barium-promoted cobalt catalyst supported on magnesium-lanthanum mixed oxide for ammonia synthesis.

Ammonia synthesis was performed over a barium-promoted cobalt catalyst supported on magnesium–lanthanum mixed oxide. The rate of NH3 formation over this catalyst was about 3.5 times higher than that over the unpromoted catalyst at 9 MPa and 400 °C. Furthermore, no sign of thermal deactivation was observed during long-term overheating at 600 °C for 360 h. The results of physicochemical studies, including XRPD, DRIFTS, H2-TPD, CO2-TPD, Nads + H2 TPSR and kinetic analysis, revealed that the addition of Ba promoter increased the surface basicity of the catalyst and modified the adsorption properties of the Co surface towards H2 and NH3. The decreased adsorption strength of the corresponding sites towards hydrogen and ammonia resulted in greater availability of active sites in the Ba-promoted cobalt catalyst. These characteristics are considered to have a profound effect on the performance of this catalyst in NH3 synthesis.

Enhanced CO2 methanation at mild temperature on Ni/zeolite from kaolin: effect of metal-support interface.

Catalytic CO2 hydrogenation to CH4 offers a viable route for CO2 conversion into carbon feedstock. The research aimed to enhance CO2 conversion at low temperature and to increase the stability of Ni catalysts using zeolite as a support. NaZSM-5 (MFI), NaA (LTA), NaY (FAU), and NaBEA (BEA) synthesized from kaolin were impregnated with 15% Ni nanoparticles in order to elucidate the effect of surface area, porosity and basicity of the zeolite in increasing Ni activity at mild temperature of ∼200 °C. A highly dispersed Ni catalyst was produced on high surface area NaY meanwhile the mesoporosity of ZSM-5 has no significant effect in improving Ni dispersion. However, the important role of zeolite mesoporosity was observed on the stability of the catalyst. Premature deactivation of Ni/NaA within 10 h was due to the relatively small micropore size that restricted the CO2 diffusion, meanwhile Ni/NaZSM-5 with a large mesopore size exhibited catalytic stability for 40 h of reaction. Zeolite NaY enhanced Ni activity at 200 °C to give 21% conversion with 100% CH4 selectivity. In situ FTIR analysis showed the formation of hydrogen carbonate species and formate intermediates at low temperatures on Ni/NaY, which implied the efficiency of electron transfer from the basic sites of NaY during CO2 reduction. The combination of Ni/NaY interfacial interaction and NaY surface basicity promoted CO2 methanation reaction at low temperature.

Surface basicity mediated rapid and selective adsorptive removal of Congo red over nanocrystalline mesoporous CeO2.

Herein we first report surface basicity mediated rapid and selective adsorptive removal of organic pollutants over nanocrystalline mesoporous CeO2. The role of surface features in controlling the selectivity and efficiency of adsorption is well known. Nevertheless, the possibility of tuning the adsorption capacity and selectivity of adsorbents through their surface characteristics remains less explored. In this work, the surface basicity of mesoporous CeO2 nanoparticles was improved by Er3+ doping under two different reaction conditions: via sol–gel and sol–hydrothermal methods. The nature and amount of surface basic sites were determined with the help of CO2 temperature programmed desorption (TPD). The adsorption capacity and selectivity of four different CeO2 samples were investigated using Congo red, methyl orange, and methylene blue as the model pollutants. From the adsorption studies, Er3+ doped CeO2 synthesized by the sol–gel method, having the highest amount of surface basic sites, proved to be the most efficient and highly selective adsorbent among the four developed variants of CeO2 towards Congo red. According to the proposed mechanism, surface basicity can be employed as a controlling parameter capable of tuning the adsorption capacity as well as the selectivity of CeO2 towards organic pollutants.

CeO2-Promoted Ni/SiO2 Catalysts for Carbon Dioxide Reforming of Methane: The Effect of Introduction Methodologies

Three typical methods, subsequent coating, co-impregnation and sequential impregnation, were employed to investigate the effect of introduction methodologies for CeO2-promoted Ni/SiO2 catalysts. The CeO2@Ni/SiO2 catalyst prepared with the subsequent coating method was found to exhibit the best initial activity and superior long-term stability in CO2 reforming of methane. Comparative characterizations documented that small Ni size and intimate Ni–CeO2 contact were generated on the CeO2@Ni/SiO2 catalyst, leading to excellent reforming activity. In addition, pronounced redox property and strong surface basicity were created on the CeO2@Ni/SiO2 catalyst, resulting in exceptional coke resistance and thus superior long-term stability. This work unravels the impact of various introduction methods on the catalyst structure, which would help design robust nanocomposite catalysts with outstanding catalytic performance.

Understanding the role of soft linkers in designing hepatzine-based polymeric frameworks as heterogeneous (photo)catalyst

The emerging class of heptazine-based polymeric materials has shown potential candidature as photocatalyst materials for hydrogen evolution. At the same time, they have shown promising application as solid base materials to catalyse various organic transformations. Thus, the material design rationale needs to be developed around the heptazine-based polymeric frameworks in order to specifically design task specific materials. Herein, we utilised controlled reaction conditions to synthesize the desired polymeric networks with trichloroheptazine as precursor. Material design strategy employed nitrogen rich [tris(2-aminoethylamine) and hydrazine] as soft linkers to understand the effect on band structure of developed heptazine-based polymeric networks. The developed polymeric networks were explored as platform to study systematically the effect on their respective photophysical properties and understand their surface basicity. The framework having aminoalkyl linker showed superior activity in photocatalysis as well as heterogeneous base catalysis. Further, model catalysts revealed the importance of N-atoms as active basic sites in these systems.

Beyond flower-like structure – The synergy within Pd/Ni-Al hydrotalcite for base-free oxidation of benzyl alcohols

A highly efficient supported metal catalyst, Pd/Ni-Al hydrotalcite with flower-like structure was synthesized and applied for catalytic oxidation of benzyl alcohols; affording >99 % conversion and 94–100 % selectivity in a base-free solution. The surface basicity and cation-oxygen mode in the layer of hydrotalcite were found to be pronouncedly associated with the changes of morphologies of the Ni-Al hydrotalcites. Compared to negligible activity by Ni-Al hydrotalcite itself, low efficiency by Pd nanoparticles or its simple mixture with Ni-Al hydrotalcite, a significant enhancement in the catalytic activity by the Pd deposited on flower-like Ni-Al hydrotalcites suggested a synergistic effect occurred between Pd and well-structured Ni-Al hydrotalcite. A plausible mechanism for the catalytic reaction involving the formation of metal-alkoxide and metal-hydroperoxide intermediates was postulated based on the control reactions, FTIR and XPS analysis and Hammett experiment.

A strategy for the enhancement of trapping efficiency of gaseous benzene on activated carbon (AC) through modification of their surface functionalities.

Facile modification is a common, but effective, option to improve the uptake removal capacity of of activated carbon (AC) against diverse target volatile organic compounds (VOCs; e.g., benzene) in gaseous streams. To help design the routes for such modification, this research built strategies to generate three types of modified ACs by incorporating amine/sulfur/amino-silane groups under solvothermal or microwave (MW) thermal conditions. The adsorption performance has been tested using a total of six types of AC sorbents (three modified+three pristine forms) for the capture of 1Pa benzene (1atm and 298K). The obtained results are evaluated in relation to their textural properties and surface functionalities. Accordingly, the enhancement of AC surface basicity (e.g., point of zero charge (PZC)=10.25), attained via the silylation process, is accompanied by the reduced adsorption of benzene (a weak base). In contrast, ACs amended with amine/sulfur (electron-donating) groups using the MW technique are found to acquire high surface acidity (PZC of 5.99-6.05) to exhibit significantly improved benzene capturing capability (relative to all others). Their uplifted performance is demonstrated in terms of key performance metrics such as breakthrough volume (BTV10%: 163→443Lg-1), adsorption capacity (Q10%: 4.82→13.6mgg-1), and partition coefficient (PC10%: 0.516→1.67molkg-1 Pa-1). Based on the kinetic analysis, the overall adsorption process is found to be governed by pore diffusion as the main rate-determining step, along with surface interaction mechanisms. The results of this research clearly support the critical role of surface chemistry of AC adsorbents and their textural properties in upgrading air/gas purification systems.