BaO Catalysts Research Articles

Photocatalytic Activity of BaAl2O4 for Water Purification.

Degradation of dyes under natural light sources is one of the most active research areas in basic science for greener technology. In this context, the photocatalytic activity of semiconductors has received massive attention in solving water treatment-related issues as these possess enormous potential for degrading organic impurities. Here, we report that barium aluminate (BaAl2O4, BAO), which has been extensively studied for photoluminescence applications, is found to be a highly potent candidate for photocatalytic activities. We have explored the degradation of dyes (meant for water purification) by using the photocatalytic properties of pure and Dy- and Yb-codoped BAO. Crystal structure, electron microscopy, and Raman analysis of the autocombustion-synthesized pure and codoped BAO samples revealed significant morphological changes such as increased particle size and stabilization of rod-like structures. UV-vis absorbance measurements confirm the presence of multiple bandgaps in the BAO samples, which is substantiated by X-ray absorption spectroscopy measurements. Photocatalytic degradation studies of methylene blue (MB) dye (with different catalyst concentrations, dopings, and MB dye concentrations) have been carried out by using BAO. The kinetics of the photocatalytic degradation measurements has been explained by the Boltzmann distribution function, and the fastest (in less than 40 min), with more than 99% degradation of MB impurity, is reported here for the first time in BAO compounds. Synthesized BAO samples show excellent cyclic stability, which is essential for their potential applications in environmental remediation. The trade-off between the enhancement of surface area and increased particle size is considered the key parameter for controlling the photocatalytic performance of the BAO catalyst after Dy and Yb codopings.

Biodiesel production from transesterified yellow grease by ZSM-5 zeolite-supported BaO catalyst: process optimization by Taguchi’s experimental design approach

Methanolysis of yellow grease (YG) was performed to synthesize its corresponding methyl ester (YGME) using BaO loaded on ZSM-5 (BaO/ZSM-5) as a heterogeneous base catalyst that was prepared via metallic solution hydrolysis method and characterized using N2 adsorption–desorption (BET), surface basicity, XRD, TGA/DTA, SEM, FTIR and Raman techniques.### The Taguchi design approach was utilized to optimize the transesterification process factors, and among the parameters studied, calcination temperature was found to have a significant influence on YGME yield. At 70 ℃ for 3 h, a YGME yield of 95.9 ±0.94\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\pm 0.94$$\\end{document}% was obtained using a methanol/YG molar ratio of 15:1 and 1 g (2 wt.% of YG used) of BaO/ZSM-5 sample calcined at 700 ℃. The BaO/ZSM-5 catalyst was reused six times with only a 15% decrease in activity.

Advancements in low-temperature NH3-SCR of NOx using Ba-based catalysts: a critical review of preparation, mechanisms, and challenges.

Presently, selective catalytic reduction (SCR), with either carbon monoxide, urea, hydrocarbons, hydrogen, or ammonia as a reductant, has become a nitrogen oxide (NOx) removal technology (NOx conversion) of many catalytic companies and diesel engine exhaust gas. Although, there exists a serious threat of low-temperature limitations. So far, certain scientists have shown that barium-based (Ba-based) catalysts have the potential to be highly effective at SCR of NOx at low temperatures when ammonia is used as the reducing agent. The process of NOx storage and reduction which alternate SCR is known as the Lean NOx trap. Herein, we give the condensed advancements and production of the catalysts that involve BaO in low-temperature NH3-SCR of NOx, the advantages of BaO catalysts compared to the recently hot electrocatalysis, the stability of BaO catalyst materials, and the condensed advancements and production of the catalysts that involve BaO in low-temperature NH3-SCR of NOx. These catalysts are viewed in the light of their preparation method, particulate, and posture in mixed oxides. Also, the characteristic features of Ba-based catalysts are carefully considered and briefed under the following areas: preparation method and precursor, crystallinity, calcination temperature, morphology, acid sites, the specific surface area for reaction, redox property, and activation energy of catalysts. More to these are the discussions on Eley-Rideal [E-R] and Langmuir-Hinshelwood [L-H] mechanisms, the H2O/SO2 and O2 permissiveness, and the NH3-SCR reaction mechanism over Ba-based catalysts highlighting their possible effects. Finally, we proposed the prospect and the likely future research plan for the low-temperature NH3-SCR of NOx.

Reactive Extraction for Fatty Acid Methyl Ester Production from Castor Seeds Using a Heterogeneous Base Catalyst: Process Parameter Optimization and Characterization

Fatty acid methyl ester (FAME) from oil seeds is conventionally produced via a two/three-process-step method: extraction of oil and subsequent esterification/transesterification to fatty FAME (biodiesel). However, in the present study, we investigated the production of castor kernel oil (CKO) FAME by reactive extraction for extraction and transesterification in a single process using a heterogeneous catalyst. The content of oil that can be extracted was checked by investigating several nonreactive extraction parameters such as solvent type (polar, nonpolar, and mixture), the solvent to kernel ratio, and extraction time. Maximum oil was extracted using methanol as a solvent with a methanol-to-seed ratio of 6.25:1 for 6 h extraction time. The viscosity of CKO obtained by nonreactive extraction was reduced from 288.83 to 19.04 mm2/s by reactive extraction using a 4.09 wt % catalyst concentration (BaO) and a 330.9:1 methanol-to-oil molar ratio for 6 h reaction time at 64 °C. Reactive extraction for transesterification of CKO was performed using BaO, CaO, and ZnO heterogeneous catalysts. BaO results in the increased yield of CKO FAME compared to other catalysts. Central composite design (CCD) using the response surface methodology (RSM) was implemented to design the experimental matrix, process parameter optimization, maximize the yield of CKO FAME, and investigate interaction effects of parameters such as reactive extraction temperature (55-65 °C), catalyst concentration (3-5 wt %), and methanol-to-oil molar ratio (175:1-350:1) on the yield of CKO FAME. A second-order model equation with a p-value < 0.05 and an R 2 value near 1.0 was obtained to predict the yield using the input parameters. The maximum yield CKO FAME of 96.13 wt % with 94.4% purity of produced CKO FAME was obtained at a catalyst concentration of 4.09 wt % and a methanol-to-oil molar ratio of 330.9:1 for 6 h with a reaction temperature of 64 °C. Therefore, a comparable conversion of castor seed oil triglyceride (96.13 wt %) was obtained in a single step directly from castor seeds. Furthermore, the rheological behavior investigation of castor kernel oil and castor methyl ester revealed that the dynamic viscosity of both samples was found to be dependent on triglyceride content and temperature.

Kinetics of Transesterification of Croton megalocarpus Oil Using Alkaline Earth Catalysts with Conventional and Microwave Heating

Transesterification kinetics of Croton megalocarpus oil to produce fatty acid methyl esters (FAME) was studied using homogeneous NaOH and heterogeneous alkaline earth Nano MgO, MgO, Nano CaO, CaO, Reoxidized CaO, SrO, and BaO catalysts. Characteristic surface, bulk, and chemical properties of the heterogeneous catalysts were obtained which included surface area, pore properties, scanning electron micrography, X-ray diffraction, basic strength, and basicity. The catalyst porosity varied as Nano MgO &gt; Nano CaO &gt; MgO &gt; CaO &gt; CaO-RO &gt; SrO &gt; BaO and basicity as BaO &gt; SrO &gt; Nano CaO &gt; CaO RO &gt; CaO &gt; Nano MgO &gt; MgO. Catalysts NaOH, BaO, SrO, and Nano CaO gave a good FAME yield (&gt;50%), and reaction order and rate constant have been reported for these catalysts, for both conventional heating and microwave irradiation. The overall reaction for NaOH was of 1st order for microwave irradiation with respect to triglyceride and of 2nd order with respect to triglyceride under conventional heating. For the heterogeneous catalysts, the overall reaction was of 3rd order, 2nd order with respect to triglyceride and 1st order with respect to methanol for both heating methods. Reaction rate constants for microwave irradiation were higher than those for conventional heating due to faster reaction rates under such heating. BaO was the most active heterogeneous catalyst, followed by SrO and Nano CaO, which was in accordance with their basicity.

Effect of the Amount of BaO Catalyst on the Selective Acetylation of Benzyl Alcohols and Doxycycline Degradation

In this study, BaO nanoflower-like was prepared by using a template, and identified using a variety of techniques. The sample was characterized by XRD measurements, scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS) and energy dispersive X-ray spectroscopy (EDX). The catalytic activity of BaO system in the acetylation of alcohols was studied. The formation of products proceeds on the catalysts with predominantly strong basic sites. This catalyst is inexpensive and easy to handle, and the acetylation of hydroxyl groups using this catalyst only required a low loading of the catalyst. The catalytic degradation of doxycycline (DOXY) has been investigated in aqueous phase using MgO and BaO nanostructures.

Numerical Simulations of the flow field and chemical reactions of the Storage/Oxidation process within a NSC Pt - BaO Catalyst

A NOx Storage Catalyst (NSC) has been studied by means of reactive CFD simulations. In the scenario of automotive pollutant emission reduction, due to the stringent regulation, the detailed description of the chemical and physical phenomena within catalysts represents a key point in order to improve their conversion efficiency. The active part of the catalyst has been simulated as a porous medium. In this zone, surface reactions take place, which are modelled by means of an Arrhenius chemical kinetic approach, involving the Pt and BaO sites on the active surface of the matrix. Actually, two chemical mechanisms are considered, the simplest involves only BaO site, the other one includes both BaO and Ptsites. Both models are validated against data available in the literature and then applied to a real automotive catalyst geometry. Thus, a detailed description of the spatial distribution of the species is provided for both models. Lean condition is simulated in order to check the catalyst behaviour according to experimental results.

The effects of BaO on the catalytic activity of La1.6Ba0.4NiO4 in direct decomposition of NO

The La1.6Ba0.4NiO4-x%BaO (x=0, 5, 10, 15, 20, 25, 30) catalysts were prepared by heating the mixture of Ba(NO3)2 and La1.6Ba0.4NiO4 in situ, and their catalytic performances were evaluated for NO direct decomposition. The results showed that the activities of the La1.6Ba0.4NiO4-x%BaO catalysts had been improved with the increasing of BaO amount. Among these catalysts, the La1.6Ba0.4NiO4-20%BaO exhibited the best catalytic performance for NO direct decomposition, and the yield of N2 kept 57% during 500h at 923K in the absence of O2, even the concentration of O2 was 0.2% in the feed, the N2 yield still up to 57% at 923K. So much higher activity for the perovskite(-like) oxides catalysts at such reaction temperature was first observed. In order to understand the role of BaO, a serial of experiments and characterizations were carried out on the La1.6Ba0.4NiO4-x%BaO catalysts. The results revealed that the number of chemical adsorption oxygen adsorbed on the oxygen vacancies increased and the mobility of the lattice oxygen could be improved due to the BaO addition. Moreover, BaO may play an important role in NOx transportation and storage, which is favorable for the regeneration of the active sites.

Biodiesel Production on MgO, CaO, SrO and BaO Oxides Supported on (SrO)(Al2O3) Mixed Oxide

The transesterification of rapeseed oil with methanol was investigated over MgO, CaO, SrO, BaO catalysts supported on binary (SrO)(Al2O3) oxide. The reaction was carried out using a fixed-bed reactor under atmospheric pressure. The activity results showed that addition of metal oxides into mixed Sr–Al oxide improves catalytic activity and fatty acid methyl esters yield in transesterification process. The physicochemical characteristics of prepared catalysts were analyzed by X-ray diffraction and TPD-CO2 methods. The highest triglycerides (TG) conversion and methyl ester yield were obtained for 10 % Sr/(SrO)(Al2O3) catalysts calcined in air at 600 °C for 4 h. The catalytic activity in the studied reaction can be described by the following series: 10 % Sr/(SrO)(Al2O3) > 10 % Ca/(SrO)(Al2O3) > 10 % Ba/(SrO)(Al2O3) > 10 % Mg/(SrO)(Al2O3) > (SrO)(Al2O3). It was proven that addition of the metal oxide into (SrO)(Al2O3) binary system improves the TG conversion to biodiesel and yield of fatty acid methyl esters in transesterification reaction.

Different dispersions of group II catalysts over SBA-15 and MCM-41: Effects on transesterification reactivity

Activities of CaO catalysts on SBA-15 and MCM-41 have been compared in transesterification and SBA-15 supported samples are invariably more active than those on MCM-41. Increased activity is not due to diffusional effects (as measured using substrates of differing size) but rather to increased dispersion of CaO on SBA-15 (as measured using NOx TPD). The effect, i.e. increased reactivity of SBA-15 supported catalysts being related to increased dispersion, is also noted in supported BaO catalysts while supported MgCO3 catalysts show little variation in dispersion (or in reactivity) as a function of the support used.

Spatiotemporal behavior of Pt/Rh/CeO2/BaO catalyst during lean–rich cycling

The experimental system that utilized an optical fiber and a spatially resolved capillary inlet mass spectrometer to study the dynamic oxygen storage capacity of ceria containing LNT catalyst during periodic lean (oxygen)–rich (propylene) operation. • Combined measurement of intrachannel temperature and concentration. • Detailed insight about the dynamics of a transient exothermic catalytic reaction. • Oxidation and reduction chemistry with ceria plays important role during cycling. • Ceria enables a more efficient oxidation to total oxidation products. • Cycling leads to much higher production of partial oxidation products H 2 and CO. Experiments were conducted to determine the impact of key operating variables (ceria loading, space velocity, cycle time, and rich pulse intensity) on the oxygen storage and release process of a Pt/Rh/CeO 2 /BaO monolithic catalyst during periodic lean (oxygen)–rich (propylene) operation. The concentrations were measured by spatially-resolved capillary inlet mass spectrometry (SpaciMS), and the temperature profile was measured by coherent optical frequency domain reflectometry (c-OFDR), providing detailed insight into the spatio-temporal features of the reaction system. The experiments revealed that the addition of ceria increased the breakthrough time of the propylene during a lean-to-rich transition due to an increased oxidation rate. Hydrogen was formed in the upstream and was consumed in the downstream section of the catalyst by reaction with ceria. Increasing the space velocity increased the upstream hydrogen formation rate and decreased its downstream oxidation rate. Increasing the lean and rich durations (while keeping their duration ratio constant) increased the oxygen uptake but resulted in propylene breakthrough and decreased the solid temperature. Increasing the rich period (at a fixed rich feed and total cycle time) allowed the catalyst to release more oxygen. A comparison of the ceria-containing catalyst to one without ceria revealed a more efficient complete oxidation for the former, while a comparison of the periodic to stationary operation revealed that less than half the propylene was converted to CO 2 by the former.

Synthesis of Highly Effective CeO x –MnO y –BaO Catalysts for Direct NO Decomposition

Ce–Mn mixed oxides with a Mn/(Ce + Mn) molar ratio of 0.25 were prepared by solvothermal (ST-1) and co-precipitation (CP) methods, and Ba was loaded on the Ce–Mn oxides. In addition, CeO2–MnO x –BaO catalysts with various compositions were directly prepared by the solvothermal (ST-2) method. The NO decomposition activities of these catalysts were examined. Among the catalysts examined, the ST-2 catalyst having a nominal composition of Ce0.8Mn0.15Ba0.05O x exhibited the highest activity; 77% NO conversion to N2 was attained at 800 °C. These catalysts were characterized by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The Raman and XPS results indicate that the CP catalyst had larger amounts of the BaMnO3-δ and/or Mn3O4 phases. The ST-1 and ST-2 catalysts had highly dispersed Ba species on the surface. The ST-2 catalyst had Mn species with the lowest binding energy of Mn 2p and also had a high population of oxygen vacancies in the ceria lattice, suggesting that Mn species with a low oxidation state contributes to the formation of oxygen vacancies, which play an important role in this reaction.

Direct Decomposition of NO into N2 and O2 on C-type Cubic Y2O3–ZrO2 and Y2O3–ZrO2–BaO

Abstract Catalytic activities for direct NO decomposition were investigated on C-type cubic Y2O3–ZrO2 and Y2O3–ZrO2–BaO prepared by coprecipitation. Introduction of excess oxide anions in the Y2O3 lattice was achieved by partial substitution of the Y3+ sites with Zr4+, and high NO decomposition activity was obtained for the (Y0.97Zr0.03)2O3.03 catalyst. In addition, the catalytic activity was further enhanced by partial substitution of the Y3+ sites in the Y2O3–ZrO2 solid solution with Ba2+, and the (Y0.89Zr0.07Ba0.04)2O3.03 catalyst exhibited the highest NO decomposition activity among the samples prepared; NO conversion to N2 reached 90% at 1173 K in the absence of O2 (NO/He atmosphere), and a relatively high conversion ratio was observed even in the presence of O2, H2O, or CO2, compared with the activities of conventional direct NO decomposition catalysts. These results indicate that the C-type cubic Y2O3–ZrO2–BaO catalyst is a new potential candidate for direct NO decomposition.

Transesterification kinetics of Camelina sativa oil on metal oxide catalysts under conventional and microwave heating conditions

The reaction kinetics of transesterification of Camelina sativa oil using metal oxide catalysts under the conventional heating and the microwave-heating conditions were investigated. The transesterification reaction rates and the fatty acid methyl ester (FAME) conversion rates were determined using heterogeneous metal oxide catalysts, i.e., BaO, CaO, MgO and SrO and two different heating methods. It was observed during the kinetic studies in this work that the BaO and SrO catalysts generated higher FAME yields than the CaO and MgO catalysts. A comparison between the conventional heating and the microwave-assisted transesterification processes showed that the reaction rate constants obtained in the microwave-assisted transesterification process are of two orders of magnitude higher than those obtained with the conventional heating method. Therefore, it can be well concluded that the heating method and solid catalysts play vital roles in improving the reaction kinetics and optimizing the reactors for biomass conversion to biodiesel.

Characteristics of low platinum Pt–BaO catalysts for NO x storage and reduction

The characteristics of low platinum Pt–BaO catalysts for NO x storage and reduction (NSR) were studied over three series of samples that have similar barium loadings (ca. 15 wt% Ba), namely, Pt–BaO/Al 2O 3, CoO x promoted Pt–BaO/Al 2O 3 and Pt–BaO/ZrO 2–Al 2O 3 catalysts. The catalysts were calcined at 800 °C and their NSR performances were evaluated under cyclic lean (1000 ppm NO and 10 vol% O 2 in Ar)/rich (1 vol% H 2 in Ar) conditions with particular attention paid to detect the possible harmful by-products, i.e., NH 3 and N 2O, during the reduction of the stored NO x under the rich condition. Lowering the Pt loading in the Pt–BaO/Al 2O 3 catalyst from 1.0 to 0.5 wt% resulted in a 15% decrease in the NO x storage capacity (NSC) under the lean condition but the N 2 selectivity under the rich condition declined dramatically (from 85% to 53%), indicating that the NO x reduction performance under the rich condition is the key to low platinum NSR catalysts. The cobalt oxides was identified as an unsuitable promoter for lowering the Pt loading; its addition into Pt–BaO/Al 2O 3 at the Pt loading of 0.5 wt% further reduced the N 2 selectivity under the rich condition although significant improvement in the NSC under lean condition could be observed. It was found instead that the use of ZrO 2–Al 2O 3 as an alternative of the Al 2O 3 support was effective in lowering the dependence on Pt loading of the Pt–BaO for the NSR catalysis since the ZrO 2–Al 2O 3 support could make the catalyst highly selective for the formation of N 2 under the rich condition, at a lower Pt loading. The overall NSR performance of a Pt–BaO/ZrO 2–Al 2O 3 catalyst with 0.5 wt% Pt was found comparable to that of its counterpart Pt–BaO/Al 2O 3 catalyst with 1.0 wt% Pt, demonstrating a viable way for developing low platinum NSR catalysts.

Catalyst size and morphological effects on the interaction of NO 2 with BaO/γ-Al 2O 3 materials

The capability of NO x storage on the supported BaO catalyst largely depends on the Ba loading. With different Ba loadings, the supported BaO component exposes various phases ranging from well-dispersed nanoclusters to large crystalline particles on the oxide support materials. In order to better understand size and morphological effects on NO x storage over γ-Al 2O 3-supported BaO materials, the adsorption structures and energetics of single NO 2 molecule, as well as NO x + NO y (NO 2 + NO 2, NO + NO 3 and NO 2 + NO 3) pairs on the BaO/γ-Al 2O 3(1 0 0), (BaO) 2/γ-Al 2O 3(1 0 0), and (BaO) 5/γ-Al 2O 3(1 0 0) surfaces were investigated using first-principles density functional theory calculations. A single NO 2 molecule prefers to adsorb at basic O Ba site forming anionic nitrate species. Upon adsorption, a charge redistribution in the supported (BaO) n clusters occurs. Synergistic effects due to the interaction of NO 2 with both the (BaO) n clusters and the γ-Al 2O 3(1 0 0) support enhance the stability of adsorbed NO 2. The interaction between NO 2 and the (BaO) n /γ-Al 2O 3(1 0 0) catalysts was found to be markedly affected by the sizes and morphologies of the supported (BaO) n clusters. The adsorption energy of NO 2 increases from −0.98 eV on the BaO/γ-Al 2O 3(1 0 0) surface to −3.01 eV on (BaO) 5/γ–Al 2O 3(1 0 0). NO 2 adsorption on (BaO) 2 clusters in a parallel configuration on the γ-Al 2O 3(1 0 0) surface is more stable than on dimers oriented in a perpendicular fashion. Similar to the bulk BaO(1 0 0) surface, a supported (BaO) n cluster-mediated electron transfer induces cooperative effects that dramatically increase the total adsorption energy of NO x + NO y pairs on the (BaO) n /γ-Al 2O 3(1 0 0) surfaces. Following the widely accepted NO 2 storage mechanism of BaO + 3NO 2(g) → Ba(NO 3) 2 + NO(g), our thermodynamic analysis indicates that the largest energy gain for this overall process of NO x uptake is obtained on the amorphous monolayer-like (BaO) 5/γ-Al 2O 3(1 0 0) surface. This suggests that γ-Al 2O 3-supported BaO materials with ∼6–12 wt% loadings may provide optimum structures for NO x storage.

Ultrasonic-assisted biodiesel production process from palm oil using alkaline earth metal oxides as the heterogeneous catalysts

The ultrasonic-assisted transesterification of palm oil in the presence of alkaline earth metal oxide catalysts (CaO, SrO and BaO) was investigated. Batch process assisted by 20 kHz ultrasonic cavitation was carried out to study the effect of reaction time (10–60 min), alcohol to palm oil molar ratio (3:1–15:1), catalysts loading (0.5–3%) and varying of ultrasonic amplitudes (25–100%). The activities of the catalysts were mainly related to their basic strength. The catalytic activity was in the sequence of CaO < SrO < BaO. At optimum conditions, 60 min was required to achieve 95% yield compared to 2–4 h with conventional stirring. Also, the yields achieved in 60 min increased from 5.5% to 77.3% (CaO), 48.2% to 95.2% (SrO), and 67.3% to 95.2 (BaO). Fifty percentage amplitude of ultrasonic irradiation was deemed the most suitable value and physical changes on the catalysts after the ultrasonic-assisted reaction were successfully elucidated. BaO catalyst underwent relatively more severe activity drop in the catalyst reusability test. Catalysts dissolution was found to be mainly responsible for activity drop of the reused catalysts, especially with BaO catalyst.

Optimization of ultrasonic-assisted heterogeneous biodiesel production from palm oil: A response surface methodology approach

The use of ultrasonic processor in the heterogeneous transesterification of palm oil for biodiesel production has been investigated. Response surface methodology was employed to statistically evaluate and optimize the biodiesel production process catalyzed by two alkaline earth metal oxide catalysts i.e. BaO and SrO. SEM, surface analysis, AAS analysis and the Hammett indicator methods were used for characterization of the catalysts. Four different variables including reaction time (10–60 min), alcohol to oil molar ratio (3:1–15:1), catalyst loading (0.5–3.0 wt.%) and ultrasonic amplitude (25–100%) were optimized. Mathematical models were developed and used to predict the behavior of the process. The models were able to accurately predict the biodiesel yield with less than 5% error for both catalysts. The basic strength of the catalysts was the main reason of their high activities. This study confirmed that the ultrasonic significantly improved the process by reducing the reaction time to less than 50 min and the catalyst loading to 2.8 wt.% to achieve biodiesel yields of above 95%. The optimum alcohol to oil ratio was found to be at 9:1 while the best amplitudes were ∼ 70 and ∼ 80% for the BaO and SrO catalysts, respectively.

Alumina and Alumina–Baria Supported Cobalt Catalysts for DeNO x : Influence of the Support and Cobalt Content on the Catalytic Performance

Co/Al2O3 and Co/Al2O3–BaO catalysts with low cobalt loading (0.1, 0.3 and 1 wt%) for the selective catalytic reduction (SCR) of NO x by C3H6 were prepared. The distribution of cobalt species was investigated by UV–vis diffuse reflectance spectroscopy and by H2-TPR in order to identify the active cobalt species in hydrocarbons (HC)-selective catalytic reduction (SCR). It was found that the nature of cobalt species strongly depends on the cobalt loading as well as on the properties of the support. The barium addition to the alumina slows down solid state diffusion processes, improving the thermal stability of the support and preventing diffusion of cobalt into the bulk. Highly dispersed surface Co2+ species over alumina were identified as active sites in the NO-SCR process. Accordingly, a high concentration of surface Co2+ sites in Co 1 wt%/Al2O3 improves the catalytic performance in NO-SCR, the long term stability as well as the water tolerance. On the contrary, the formation of Co3O4 particles in Co 1 wt%/Al2O3–BaO promotes the propylene oxidation by oxygen, decreasing the activity and selectivity of the catalyst in NO reduction.

Kinetic Modeling of NOx Storage/Reduction on Pt/BaO/Al2O3 Monolith Catalysts

A balance of the complexity of the reactor model and the chemical reaction mechanism has to be made in order to predict the dynamic nature of NOx storage/reduction processes in real time. In this work, a one-dimensional, two-phase model is used to simulate the transient behavior of a monolithic Pt/BaO/Al2O3 catalyst for NOx storage/reduction. The following aspects of the process are discussed: (i) kinetics of NO and NO2 adsorption on BaO sites, (ii) effects of CO2 and H2O on NO/NO2 adsorption, and (iii) reduction of surface nitrates using H2. NOx adsorption with excess oxygen involves two kinetic routes, namely, NO2 disproportionation and direct NO adsorption, both of which form nitrates on the catalyst at 300 °C. A model with two time scales was found to be necessary to describe NO2 adsorption on the 20 wt % BaO catalyst. The model and parameters required to fit the NOx breakthrough curves suggest that CO2 and H2O in the feed reduce the number of sites for NO adsorption by changing the surface morphology of the Ba phase. The rate constants for both fast and slow NO2 uptake are decreased in the presence of CO2 and H2O, but the total capacity remains the same. Under reaction conditions, H2 reduction of surface NOx is limited by the supply of the reductant; that is, the rate of surface NOx removal is limited by the flux of inlet H2. NH3 serves as the reducing intermediate/H carrier during the H2 reduction process. The confined reduction front moving along the channel localizes the heat generation, thus leading to a surface temperature in the reduction front about 35 °C higher than the inlet gas temperature for our reaction conditions.