Types Of Adsorption Sites Research Articles

A Kinetic Model of Furfural Hydrogenation to 2-Methylfuran on Nanoparticles of Nickel Supported on Sulfuric Acid-Modified Biochar Catalyst

Lignocellulosic biomass can uptake CO2 during growth, which can then be pyrolysed into three major products, biochar (BC), syngas, and bio-oil. Due to the presence of oxygenated organic compounds, the produced bio-oil is not suitable for direct use as a fuel and requires upgrading via hydrodeoxygenation (HDO) and hydrogenation. This is typically carried out over a supported metal catalyst. Regarding circular economy and sustainability, the BC from the pyrolysis step can potentially be activated and used as a novel catalyst support, as reported here. A 15 wt% Ni/BC catalyst was developed by chemically modifying BC with sulfuric acid to improve mesoporous structure and surface area. When compared to the pristine Ni/BC catalyst, sulfuric activated Ni/BC catalyst has excellent mesopores and a high surface area, which increases the dispersion of Ni nanoparticles and hence improves the adsorptive effect and thus catalytic performance. A liquid phase hydrogenation of furfural to 2-methylfuran was performed over the developed 15 wt% Ni/BC catalyst. Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic type models for adsorption of dissociative H2 were screened based on an R2 value greater than 99%, demonstrating that the experimental data satisfactorily fit to three plausible models: competitive (Model I), competitive at only one type of adsorption site (Model II), and non-competitive with two types of adsorption sites (Model III). With a correlation coefficient greater than 99% between the experimental rates and the predicted rate, Model III, which is a dual-site adsorption mechanism involving furfural adsorption and hydrogen dissociative adsorption and surface reaction, is the best fit. The Ni/BC catalyst demonstrated comparative performance and significant cost savings over previous catalysts; a value of 24.39 kJ mol−1 was estimated for activation energy, −11.43 kJ mol−1 for the enthalpy of adsorption for H2, and −5.86 kJ mol−1 for furfural. The developed Ni/BC catalyst demonstrated excellent stability in terms of conversion of furfural (96%) and yield of 2-methylfuran (54%) at the fourth successive experiments. Based on furfural conversion and yield of products, it appears that pores are constructed slowly during sulfuric acid activation of the biochar.

Linking electron-rich Pillar[5]arene into hyper-cross-linked polymers for highly effective adsorption of iodine vapor

Four hyper-cross-linked polymers were synthesized by linking electron-rich monomers with an electron-rich cross-linker via the Friedel–Crafts reaction. Among these polymers, P4, which was constructed with decaalkyne pillar[5]arene and bibenzyl chloride, adsorbed iodine vapor with a capacity of 3.930 g g−1, outperforming most supramolecular macrocycle-based porous polymers. The pillar[5]arene macrocycle contributed various types of adsorption sites, including aromatic rings, diynes, and oxygen atoms. The abundance of effective adsorption sites and the high specific surface area (1615.5 m2 g−1) were responsible for the excellent adsorption capacity of P4. Because these polymers are easy to synthesize and regenerate and can be mass produced, they are promising candidates for large-scale applications.

Calcium isotope fractionation associated with adsorption and desorption on/from δ-MnO2

Small mineral particles present in soils, such as clay minerals and some oxyhydroxides, constitute important nutrient reservoirs. This behavior is due to the negative charges and high specific surface areas of these particles allowing them to adsorb cations such as calcium (Ca), a macronutrient that occupies key physiological and structural functions in plant metabolism. Although the chemical reactivity of clay minerals is rather well-known in the literature, especially toward macronutrients such as Ca, that of oxyhydroxides such as phyllomanganate minerals remains largely unexplored.To enhance our understanding of the mechanisms at the origin of the storage/release of the different isotopes of Ca in a soil solution, the possible fractionation between 40Ca and 44Ca during adsorption and desorption of Ca on a synthetic phyllomanganate, abiotically precipitated in the laboratory [synthetic analog of vernadite (δ-MnO2)], was studied. Experiments were performed in batch (closed system), and several parameters (time, pH of the solution, Ca concentration and nature and concentration of the desorbent) were tested to cover a large range of physicochemical conditions.This study demonstrated that the light 40Ca isotope is preferentially adsorbed on δ-MnO2, with Δ44/40Ca (the apparent fractionation of the aqueous solution at the stationnary state of adsorption compared to the initial one) of the adsorbed Ca that can reach 1.19 ± 0.15‰. The results showed that this isotopic fractionation occurs at chemical equilibrium in a closed system and that the isotopic fractionation measured in this study during Ca adsorption on phyllomanganate is significantly higher than that reported in the literature during Ca adsorption on other soil constituents such as clay minerals. At pH below 4 Ca occupies only the interlayer/basal sites whereas above this pH Ca fills interlayer/basal sites (∼86%) and edges sites (∼14%). By combining the experimental data obtained at different pH values, initial Ca concentrations and interaction times, our results suggest that isotopic signature of the Ca adsorbed on δ-MnO2 is dependent on the nature of the site involved in the adsorption step (i.e., enriched in 40Ca in the interlayer with Δ44/40Ca equal to −0.43‰ and enriched in 44Ca when bound to the edges with Δ44/40Ca equal to +3.5‰). As revealed by surface complexation modeling, such contrasting behavior between the two types of adsorption sites could be due to the bidendate nature of the Ca adsorption occurring on edges and to ion exchange of Ca2+ with H+ in the interlayer sites. Finally, desorption experiments point to total but not instantaneous Ca desorption, probably due to a partial collapse of the interlayer with some ions used to desorb Ca2+ (K+, NH4+, hexaamine-cobalt). This suggests that the amount of bioavailable Ca in soils by simple ion-exchange reactions is highly dependent on the nature of the ions which could desorb Ca present in the soil solution.

Competitive adsorption of sulfamethoxazole and bisphenol A on magnetic biochar: Mechanism and site energy distribution

Competitive adsorption and complementary adsorption between emerging pollutants has been observed in multiple studies. Investigation of the preference of pollutants for different types of adsorption sites can provide a supplementary perspective for understanding complementary adsorption. In this study, the simultaneous adsorption of two typical emerging pollutants, sulfamethoxazole (SMX) and bisphenol A (BPA), on magnetic biochar (MBC-1) was investigated. The results showed that the modification with ferric chloride optimized the surface properties of biochar (aromaticity, hydrophobicity, and oxygen-containing functional groups, etc.), and helped to remove SMX and BPA through various interactions. The equilibrium adsorption capacity of the two adsorbents was inhibited by competitive adsorption in the mixed solute systems, which was due to the same adsorption mechanism. When pH = 7, the SMX and BPA adsorption mainly involved pore filling, hydrophobic effect, π-π EDA, and hydrogen bonding. In addition, electrostatic force, surface coordination, and ion exchange have also been proven to be related to the adsorption of SMX and BPA. In the co-adsorption system, BPA's competitive advantage might be due to its superior hydrophobicity, charge property, and molecular diameter. In the competitive adsorption experiment, the total adsorption capacity (Qi) of the competitive solute exceeded the adsorption inhibition (△Qi) of the main solute, indicating that the two solutes occupied their preferred adsorption sites, which confirmed the complementary adsorption phenomenon. Complementary adsorption can be explained by the preference of SMX and BPA for different types of adsorption sites. BPA preferentially occupied high-energy sites in the co-adsorption system, such as π-π EDA interaction, ion exchange, and surface coordination. At the same time, SMX tended to be removed by hydrophobic interaction and hydrogen bonding.

Enhanced CO adsorption on α-graphyne-supported and defective graphene-supported Cu19 clusters and a modified induction energy model.

Ab initio molecular dynamics calculations were carried out to study the adsorption of CO on Cu19, α-graphyne-supported Cu19 and defective graphene-supported Cu19 clusters. The average adsorption energies on the three clusters are significantly increased by 68%, 104%, and 123% compared to the experimental value on the pristine Cu(110) surface. Furthermore, the α-graphyne-supported and defective graphene-supported Cu19 clusters exhibit greater adsorption strength than the pure Cu19 cluster, with 22% and 33% higher adsorption energies, respectively. The crystal orbital Hamilton population analysis shows that for the same type of adsorption site, the adsorption energy is linearly related to the bond interaction strength between the adsorbate and the substrate. We propose a modified induction energy model to predict the increase of chemisorption energy on α-graphyne-supported and defective graphene-supported Cu19 clusters based on the bare Cu19 cluster. The chemisorption energy enhancement predicted by the improved induction energy model has very good agreement with that calculated based on the ab initio molecular dynamics method and is more accurate than that predicted by the original induction energy model.

Diffusion in a binary mixture of molecules adsorbed on a multisite two-dimensional lattice

The diffusion in a binary mixture of species coadsorbed on a multisite square lattice is investigated by a theoretical approach (Chumak and Tarasenko, 1980) based on the non-equilibrium statistical operator method proposed by Zubarev (1961). The investigated lattice gas system is rather complex. There is a mixture of two types of particles (atoms, and/or molecules) adsorbed on a multisite lattice which consists of the three types of adsorption sites. This lattice can be subdivided onto three homogeneous square sublattices composed of the sites of the same type. As the binding energies for the molecules of distinct types adsorbed on the nonidentical sublattices are different, there are six average occupancies (coverages) describing the molecule distribution over the sublattices. A system of the balance equations, which controls the exchange of the molecules between the sublattices on the atomistic level is reduced to the diffusion equations describing the evolution of small hydrodynamic fluctuations of these coverages on the macroscopic level. The diffusion equations are written in the Onsager representation, when the driving forces are gradients of the chemical potentials and in the Fickian representation, when the driving forces are the gradients of coverages. The derivation of these equations results in the analytical expressions for the Fickian diffusivities and Onsager phenomenological coefficients. Despite the complex process of derivation, the final results are simple. The kinetic coefficients, which describe the non-equilibrium state of the molecule system, are expressed via the thermodynamic quantities calculated in the equilibrium state of the system: the chemical potentials (or activities), pair correlation functions and the isothermal susceptibilities. These expressions are derived with account of the lateral interactions between the nearest neighbor molecules. The matrix of the Fickian diffusivities has the ordinary classical form. The diffusivity is a non-symmetric 2 × 2 matrix. The Onsager coefficients are represented by a diagonal 2 × 2 matrix, where the cross terms are absent.

Simultaneous Adsorption of Gaseous Hg0 and Hg(II) by Regenerable Monolithic FeMoSx/TiO2: Mechanism and its Application in the Centralized Control of Hg Pollution in Coal-Fired Flue Gas

FeMoSx/TiO2 was investigated as a regenerable sorbent to simultaneously adsorb Hg0 and Hg(II) from coal-fired flue gas for the centralized control of Hg pollution discharged from coal-fired power plants. The performance of FeMoSx/TiO2 for Hg(II) and/or Hg0 adsorption was evaluated on a fixed-bed reactor at 80 oC, and the mutual interference between Hg0 adsorption and Hg(II) adsorption was analyzed using individual adsorption, simultaneous adsorption, and two-stage adsorption. FeMoSx/TiO2 displayed an excellent capacity for individual Hg0 adsorption (41.8 mg g-1) and a moderate capacity for individual Hg(II) adsorption (0.48 mg g-1). Two types of adsorption sites were present on FeMoSx/TiO2 for gaseous Hg adsorption (S0 and FeS2/MoS3 sites). X-ray photoelectron spectroscope and kinetic analyses demonstrated that Hg0 and Hg(II) could adsorb onto S0 sites, whereas only Hg0 was adsorbed onto FeS2/MoS3 sites. As Hg0 competed with Hg(II) for the S0 sites, the amount of Hg(II) adsorbed slightly decreased by 16% in the presence of Hg0. However, Hg0 adsorption onto the FeS2/MoS3 sites predominated over the Hg0 adsorption onto FeMoSx/TiO2 and it was not inhibited in the presence of Hg(II). Therefore, the amount of Hg0 adsorbed on FeMoSx/TiO2 was only decreased by 2% in the presence of Hg(II).

Noise Spectrum as a Source of Information in Gas Sensors Based on Liquid-Phase Exfoliated Graphene

Surfaces of adsorption-based gas sensors are often heterogeneous, with adsorption sites that differ in their affinities for gas particle binding. Knowing adsorption/desorption energies, surface densities and the relative abundance of sites of different types is important, because these parameters impact sensor sensitivity and selectivity, and are relevant for revealing the response-generating mechanisms. We show that the analysis of the noise of adsorption-based sensors can be used to study gas adsorption on heterogeneous sensing surfaces, which is applicable to industrially important liquid-phase exfoliated (LPE) graphene. Our results for CO2 adsorption on an LPE graphene surface, with different types of adsorption sites on graphene flake edges and basal planes, show that the noise spectrum data can be used to characterize such surfaces in terms of parameters that determine the sensing properties of the adsorbing material. Notably, the spectrum characteristic frequencies are an unambiguous indicator of the relative abundance of different types of adsorption sites on the sensing surface and their surface densities. We also demonstrate that spectrum features indicate the fraction of the binding sites that are already occupied by another gas species. The presented study can be applied to the design and production of graphene and other sensing surfaces with an optimal sensing performance.

Biosorption of Pb and Cd onto Polygonum sachalinense

Adsorption of Pb and Cd onto a biosorbent, carbonized Polygonum sachalinense (CPS) was investigated. The carbonization condition was 1 h at 350ºC. The adsorption behaviors of Pb and Cd onto CPS could be explained by a proposed adsorption model based on the monodentate binding of the divalent metal ions with two types of adsorption sites. The adsorption sites were considered as carboxylic and phenolic groups based on the results of Boehm titration and FT-IR analysis. The maximum adsorption capacity of CPS for the divalent metal ions was determined as 1.22 mmol/g, and it was much larger than the values reported in the previous reports. The binding affinities of Pb of the adsorption sites were considered as much higher than those of Cd based of the adsorption constants. The adsorption constants of Pb and Cd with carboxylic group were about 200–2000 times larger than the of the adsorption constants with phenolic group. The kinetics of Pb and Cd onto CPS were also investigated. It was found that the adsorption of the divalent metal ions onto the phenolic group was a rate limiting step.

Synthesis, Characterization, and Application of Magnetized Lanthanum (III)-Based Metal-Organic Framework for the Organic Dye Removal from Water

A hybrid composite based on metal-organic framework (MOF) was chemically fabricated by embedding the magnetic Fe3O4 nanoparticles within amino-functionalized porous La-MOF (MOF/NH2) to produce a highly efficient and reusable composite of MOF/NH2/Fe3O4. Different proper techniques were used for the characterization of surface morphology and chemical arrangement of the prepared MOF/NH2/Fe3O4 composite. The characterization results using various techniques including Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), Brunauer, Emmett, and Teller analysis (BET), and vibrating sample magnetometer (VSM) approved the successful fabrication of MOF with amino arms on its surface besides the well magnetization using magnetic nanoparticles. The MOF/NH2/Fe3O4 composite showed enhanced adsorption capacity (618 mg/g) toward methyl orange (MO) anionic dye which is higher than many commercial reported adsorbents due to the presence of many types of adsorption sites (NH2 groups and lanthanum sites), large surface area of MOF, and the synergetic effect of magnetic nanoparticles. Moreover, the MOF/NH2/Fe3O4 composite showed selective adsorption of MO dye from dye mixtures owing to the electrostatic attraction. Also, the MOF/NH2/Fe3O4 composite retained over 90% of its efficiency for the dye removal even after six successive cycles. So, the present study provided a practical strategy for the design of functional MOF hybrid composites. Furthermore, due to the adaptability of its architectural form, it is a potential adsorbent material for industrial wastewater treatment uses.

Electronic transport properties and quantum localization effects monitored by selective functionalization in Bernal bilayer graphene

Monitoring electronic properties of 2D materials is an essential step to open a way for applications such as electronic devices and sensors. From this perspective, Bernal bilayer graphene (BLG) is a fairly simple system that offers great possibilities for tuning electronic gap and charge carriers' mobility by selective functionalization (adsorptions of atoms or molecules). Here, we present a detailed numerical study of BLG electronic properties when two types of adsorption site are present simultaneously. We focus on realistic cases that could be realized experimentally with adsorbate concentration c varying from 0.25% to 5%. For a given value of c, when the electronic doping is lower than c we show that quantum effects, which are ignored in usual semi-classical calculations, strongly affect the electronic structure and the transport properties. A wide range of behaviors is indeed found, such as gap opening, metallic behavior or abnormal conductivity, which depend on the adsorbate positions, the c value, the doping, and eventually the coupling between midgap states which can create a midgap band. These behaviors are understood by simple arguments based on the fact that BLG lattice is bipartite. We also analyze the conductivity at low temperature, where multiple scattering effects cannot be ignored. Moreover, when the Fermi energy lies in the band of midgap states, the average velocity of charge carriers cancels but conduction is still possible thanks to quantum fluctuations of the velocity.

Adsorption modeling by two sites Langmuir type isotherm for adsorption of bisphenol-A and diethyl phthalate onto activated carbon in single and binary system

ABSTRACT Adsorption of bisphenol-A (BPA) and diethyl phthalate (DEP) onto activated carbon has been studied. The experimental adsorption data is reasonably well fitted by a two site Langmuir isotherm model. The estimated two equilibrium adsorption constants were almost the same even though the adsorbates were different. This suggested that the existence of two types of adsorption sites with different equilibrium adsorption constants for strong and weak sites on the present activated carbon surface. The equilibrium adsorption constant of strong site was 130 times larger than that of weak site, and the saturated adsorption density of weak site was 2.6 and 3.6 times larger than that of strong site for BPA and DEP, respectively. In addition, adsorption experiments of the binary system have also been carried out. Based on suggesting two type sites, two models, competitive adsorption or noncompetitive adsorption models, were attempted to apply to the experimental results. Judging from the model consideration, the noncompetitive model could describe well the adsorption isotherm in the binary system. Compared with the single system, in the binary system, the equilibrium adsorption constants were almost the same, but the saturated adsorption densities were 10% to 30% lower than that of the single system.

Theoretically predicted CO adsorption and dissociation on Ru-doped Co(1 0 0) surfaces

CO adsorption and dissociation on Ru-doped Co(100) surfaces at different CO coverage compared to clean surface were investigated based on spin-polarized density functional theory (DFT), in order to explore the effect of the initial step of Ru promoter on CO activation in cobalt-based Fischer-Tropsch synthesis (FTS). The results show that CO adsorption is highly site-dependent, the adsorption strength of CO at different types of adsorption sites is determined by the interaction between the adsorbed CO molecule and Ru-doped Co(100) surfaces. CO dissociation is promoted at hollow sites but inhibited at top and bridge sites above the Ru atoms. In addition, the amount of saturated adsorbed CO is increased while the amount of dissociated CO is decreased on the Ru-doped Co(100) surfaces at high coverage. Combining the experimental results, it is concluded that the adsorption model is preferred than substitution model for CO activation, because the increased CO molecular states in adsorption model is facile for the subsequent H-assisted dissociation on Co surface. The present work suggests that the addition of Ru promoter can improve the CO activation on Co(100) surface and pave the way for experimental research.

Ultrahigh Hydrogen Uptake in an Interpenetrated Zn 4 O-Based Metal–Organic Framework

As a highly promising candidate for hydrogen storage, crucial to vehicles powered by fuel cells, metal–organic frameworks (MOFs) have attracted the attention of chemists in recent decades. H2 uptak...

Impact of Na+ and Ca2+ Cations on the Adsorption of H2S on Binder-Free LTA Zeolites

Hydrogen sulfide is removed from natural gas via adsorption on zeolites. The process operates very effectively, but there is still potential for improvement. Therefore, in this article, the adsorption of hydrogen sulfide was investigated on eight LTA zeolites with different cation compositions. Starting with the zeolite NaA (4 A), which contains only Na+ cations, the Ca2+ cation content was gradually increased by ion exchange. Equilibrium isotherms from cumulative breakthrough curve experiments in a fixed-bed adsorber at 25°C and 85°C at 1.3 bar (abs.) were determined in the trace range up to a concentration of 2000 ppmmol. From a comparison of the isotherms of the different materials, a mechanistic proposal for the adsorption is developed, taking into account the specific positions of the cations in the zeolite lattice when the degree of exchange is increased. The shape of the isotherms indicates two energetically different types of adsorption sites. It is assumed that two mechanisms are superimposed: a chemisorptive mechanism with dissociation of hydrogen sulfide and covalent bonding of the proton and the hydrogen sulfide ion to the zeolite lattice and a physisorptive mechanism by electrostatic interaction with the cations in the lattice. As the degree of exchange increases, the proportion of chemisorption sites seems to decrease. Above an exchange degree of 50%, only evidence of physisorption can be found. It is shown that this finding points to the involvement of weakly bound sodium cations at cation position III in the chemisorption of hydrogen sulfide.

Adsorption of mandelic acid enantiomers on chiral stationary phase with grafted antibiotic eremomycin: The effect of the eluent pH

The adsorption of mandelic acid enantiomers on the Nautilus-E chiral stationary phase with eremomycin as a grafted antibiotic, as affected by value of the water-ethanol eluent under conditions of an overloaded column, was studied. Adsorption equilibrium under experimental conditions, when mandelic acid dissociates both completely and then very weakly, was studied. The adsorption isotherms of S- and R-mandelic acid were plotted by the Glueckauf method and inverse method using bi-Langmuir model, as well as the tri-Langmuir model assuming independent adsorption on three types of adsorption centers, with two of them being high-energy enantioselective (ion-exchange and molecular adsorption) and the third – the low-energy nonselective types of sites. This model takes into account the ionization of mandelic acid in the eluent and a change in the value in the mass transfer zone caused by its ionization. The saturated capacity and binding energy of all the types of adsorption sites depend on of the eluent. Nonselective interactions contribute to the adsorption of mandelic acid mainly. To determine the adsorption isotherms of mandelic acid enantiomers on Nautilus-E CSP in the absence of its dissociation and distortion of the elution profiles, the Glueckauf method and the bi-Langmuir model were identified as an acceptable choice.

A subtraction fitting method for independent determination of enantioselective and nonselective adsorption isotherms based on the single-component isotherms in the framework of the two-site model

Based on theory of two-site model, a subtraction fitting method (SFM) is proposed to independently fit enantioselective adsorption sites and the nonselective adsorption sites on the surface of chiral stationary phases (CSP) based on polysaccharide derivatives. Compared with the direct fitting method, the method allows independent fitting the isotherm models of two types of adsorption sites. By the SFM, the adsorption data of methyl mandelate on the CSP based on cellulose tri-(3, 5-dimethylphenylcarbamate) was measured. The adsorption on enantioselective sites was well fitted with Langmuir model, and the adsorption on nonselective sites was well fitted with Tóth model or Langmuir-Freundlich model. The adsorption isotherms of the enantiomers of Corey PG-lactone diol on chiral stationary phase coated with different amounts of amylose tri-(3,5-dimethylphenylcarbamate) (Wchiral selector: Wsilica = 20 : 100, 30: 100 and 40: 100, respectively) were also studied. It was found that the saturated adsorption capacities of both sites increase with the increase of the chiral selector loading. The chiral stationary phase with low chiral selector loading (Wchiral selector: Wsilica = 20 : 100) has a high true separation factor (αtrue = 16.8) and the lowest apparent separation (αapp = 1.70) due to the large nonselective adsorption, which indicates that a chromatographic support with an inert surface is important for this type of CSP.

Temporal response of biochemical and biological sensors with bimodal surface adsorption from a finite sample.

The importance of adsorption-based biochemical/biological sensors in biochemistry and biophysics is paramount. Their temporal response gives information about the presence of a biochemical/biological analyte, its concentration and its interactions with the adsorption sites (which may be an integral part of the surface itself or immobilized functionalizing molecules). Mathematical models of the temporal response taking into account as many relevant effects as possible are essential for obtaining reliable information. We present a novel model taking into account the bimodal affinity of a sensing surface (adsorption occurs on two distinct site types), and the adsorption-caused depletion of the analyte from the sample. We perform qualitative and quantitative analysis of the analyte depletion influence on the bimodal adsorption, and of the influence of the sensing surface inhomogeneity on the sensor temporal response, for different analyte concentrations and different fractions of two types of adsorption sites. Since the presented mathematical model deals with the realistic cases of the sensing surface non-uniformity and the finite amount of analyte present in the sensor reaction chamber, it enables improved accuracy in interpreting the measurement data. Our results are general, i.e. valid for any adsorption sensor (microcantilevers, plasmonics) and for arbitrary sensor dimensions.

Removal Mechanism and Effective Current of Electrocoagulation for Treating Wastewater Containing Ni(II), Cu(II), and Cr(VI)

This study aims to clarify the removal mechanism and to calculate the effective current of electrocoagulation (i.e., EC) for treating wastewater containing Ni(II), Cu(II), and Cr(VI). The adsorption behavior of various heavy metals onto Al(OH)3 coagulant generated by the EC process was investigated and the estimating method of the corresponding current was established. Results indicate that adsorption of single Ni(II) and Cu(II) by Al(OH)3 coagulant can be simulated by the Langmuir isotherm, while Cr(VI) adsorption fits the Freundlich isotherm better. As treating single heavy metal of wastewater, the removal mechanism of the EC process is the adsorption reaction. Under the coexisting condition, the Ni(II) and Cu(II) will compete for the same active sites on the Al(OH)3 surface and Cu(II) suppresses Ni(II) adsorption. As treating the coexisting heavy metals, Ni(II) removal not only associates with adsorption but also with the coprecipitation. In contrast, Cr(VI) does not compete with other metal ions for the same type of adsorption sites. Whether single or coexisting conditions, the adsorption capacity of heavy metals onto Al(OH)3 coagulants can be used to compute the necessary current to effectively remove heavy metals in the EC system.

Catalytic combustion of propane on Pd-modified Al–La–Ce catalyst – from reaction kinetics and mechanism to monolithic reactor tests and scale-up

Abstract A propane combustion catalyst was prepared by supporting of Pd on optimized multiphase composition, containing Al2O3, La2O3 and CeO2 aiming for possible application in catalytic converters for abatement of propane in waste gases. The catalyst characterization has been made by N2- physisorption, XRD, SEM/EDX, TEM and XPS. The obtained values for reaction order towards propane and oxygen are 0.57 and 0.14, respectively. The negative reaction order towards the water vapour (−0.26) shows an inhibition effect of the water molecules. According to the kinetics model calculations, the reaction pathway over Pd-modified La–Ce catalyst proceeds most probably through Langmuir–Hinshelwood mechanism with adsorption of propane and oxygen on different types of sites, dissociative adsorption of oxygen, whereupon water molecules compete with propane molecules for one and the same type of adsorption sites. For practical evaluation of the synthesized material, a sample of Pd/Al2O3–La2O3–CeO2, supported on rolled Al-containing stainless steel (Aluchrom VDM®) to form a single monolithic channel was prepared and tested. Two-dimensional heterogeneous models were used to simulate the propane combustion from laboratory reactor to full-scale adiabatic monolithic converter for ensuring an effective abatement of propane emissions.