Langmuir-Hinshelwood Mechanism Research Articles

Study on the Performance of the Zr-Modified Cu-SSZ-13 Catalyst for Low-Temperature NH3-SCR.

Cu-SSZ-13 and Zr-modified Cu-SSZ-13 catalysts with different Zr/Cu mass ratios were prepared by ion-exchange and impregnation methods, respectively. The NH3-SCR performance tests were performed using the catalyst performance evaluation device to investigate the effects of different Zr/Cu mass ratios on the catalyst ammonia-selective catalytic reduction (NH3-SCR) performance. X-ray diffraction, ICP-OES, BET, NH3 temperature-programed desorption (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectrometry, and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) were used to characterize the catalysts. The results show that the prepared Cu-SSZ-13 catalyst had good catalytic activity. Zr introduction was carried out on this basis. The results showed that proper Zr doping improved the catalytic activity at low temperatures and widened the high-temperature stage, with an optimal activity stage at a Zr/Cu mass ratio of 0.2. The NO x conversion efficiency was close to 100% at 200 °C and over 80% at 450 °C. The active species were well dispersed on the catalyst surface, and the metal modification did not change the crystal structure of the zeolite. The NH3-TPD results showed that the Zr-modified catalyst had more abundant acid sites, and the H2-TPR results indicated that the Cu species on the catalyst had excellent reducibility at low temperatures. The interaction between Cu and Zr could regulate the Cu+ and Cu2+ proportion on the catalyst surface, which facilitated the increase in the Cu+ for fast SCR reaction at low temperatures. With abundant acid sites and both SCR reactions following the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanism on the catalyst surface at a low temperature of 150 °C, more abundant acid sites and reaction paths created favorable conditions for NH3-SCR reactions at low temperatures.

Catalyst screening and reaction kinetics of liquid phase DME synthesis under reactive distillation conditions

Catalyst screening and reaction kinetics of liquid phase DME synthesis under reactive distillation conditions

Effect of morphology and simultaneous sulfation on Fe doped CeO2 for selective catalytic reduction of NOx with NH3

Effect of morphology and simultaneous sulfation on Fe doped CeO2 for selective catalytic reduction of NOx with NH3

Impact of hydronium ions on the Pd-catalyzed furfural hydrogenation

In aqueous mediums, the chemical environment for catalytic reactions is not only comprised of water molecules but also of corresponding ionized species, i.e., hydronium ions, which can impact the mechanism and kinetics of a reaction. Here we show that in aqueous-phase hydrogenation of furfural on Pd/C, increasing the hydronium ion activities by five orders of magnitude (from pH 7 to pH 1.6) leads to an increase of less than one order of magnitude in the reaction rate. Instead of a proton-coupled electron transfer pathway, our results show that a Langmuir-Hinshelwood mechanism describes the rate-limiting hydrogen addition step, where hydrogen atom adsorbed on Pd is transferred to the carbonyl C atom of the reactant. As such, the strength of hydrogen binding on Pd, which decreases with increasing hydronium ion concentration (i.e., 2 kJ molH2−1 per unit pH), is a decisive factor in hydrogenation kinetics (rate constant +270%). In comparison, furfural adsorption on Pd is pH-independent, maintaining a tilted geometry that favors hydrogen attack at the carbonyl group over the furan ring.

Crystal plane induced metal-support interaction in Pd/Pr-CeO2 catalyst boosts H2O-assisted CO oxidation

• H 2 O promotes the CO oxidation on Pr-CeO 2 nanorods supported Pd catalyst. • High dispersed Pd and oxygen vacancy served as the active sites for CO and O 2 activation in the presence of H 2 O. • CO oxidation mainly follows the H 2 O-mediated L-H mechanism and formate pathway in the presence of H 2 O. • Pd/Pr-CeO 2 -NRs catalyst exhibits outstanding SO 2 resistance in the presence of 100 ppm SO 2 . Catalytic oxidation is an effective method to remove CO in exhaust gas, yet it is challenging to enhance the H 2 O tolerance of catalysts at low temperature due to the strong competitive adsorption between H 2 O and reactants (CO and O 2 ). Here, we report that the precise control of the metal-support interaction by regulating the support crystal plane of Pd/Pr-CeO 2 catalysts leads to highly efficient CO oxidation catalysts under wet conditions. It has been found that the addition of H 2 O inhibits the CO oxidation activity of Pr-CeO 2 nano-cube and octahedron supported highly dispersed Pd catalysts, but enhances the CO oxidation activity over Pr-CeO 2 nanorod supported highly dispersed Pd catalysts. After introduction of H 2 O in feed gas, the T 99 (temperature to achieve 99% conversion of CO) decreases from 157 °C to 115 °C for Pd/Pr-CeO 2 -NRs (Nanorods) catalyst at a gas hourly space velocity of 70, 000 h -1 and remains stable for more than 2400 min in the presence of H 2 O. Systematic characterization reveals that the (110) crystal plane of CeO 2 nanorod enhance the interaction between Pd species and Pr-CeO 2 support, resulting in the formation of abundant high dispersed Pd-oxygen vacancy (Ov) active sites. The kinetics study and in-situ DRIFTS characterization confirmed that CO oxidation Pd/Pr-CeO 2 -NRs mainly follows the H 2 O-mediated Langmuir-Hinshelwood mechanism in the presence of H 2 O. H 2 O promote the formation of active OH groups and accelerate CO oxidation through formate pathway at low temperature. In contrast, the CO oxidation follow traditional MvK mechanism in the absence of H 2 O.

Oxidation of Phenolic Aldehydes by Ozone and Hydroxyl Radicals at the Air-Solid Interface.

Biomass burning emissions contain abundant phenolic aldehydes (e.g., syringaldehyde, vanillin, and 4-hydroxybenaldehyde) that are oxidized during atmospheric transport, altering the physicochemical properties of particulates. Herein, the oxidative processing of thin films made of syringaldehyde, vanillin, and 4-hydroxybenaldehyde is studied at the air-solid interface under a variable O3(g) molar ratio (410 ppbv-800 ppmv) and relative humidity (0-90%). Experiments monitored the absorption changes of C=C, C=O, and -COOH vibration changes during the oxidation of thin films by transmission Fourier transform infrared spectroscopy (FTIR). Selected spectroscopic features of aromatic ring cleavage by O3(g) revealed the production of carboxylic acids. Instead, monitoring O-H stretching provided a comparison of a hydroxylation channel from in situ produced hydroxyl radical. The overall oxidation reactivity trend syringaldehyde > vanillin > 4-hydroxybenzladehyde can be explained based on the additional electron density from methoxide substituents to the ring. The reactive uptake coefficient of O3(g) increases for higher relative humidity, e.g., for syringaldehyde by 18 and 215 times at 74% and 90% relative humidity (RH), respectively, as compared to dry conditions. A Langmuir-Hinshelwood mechanism fits well the kinetics of oxidation under a variable O3(g) molar ratio at 74% RH, providing useful information that should be included in atmospheric chemistry models.

Promoting electrocatalytic hydrogenation of 5-hydroxymethylfurfural using buffer electrolytes as proton-donating motifs: Theoretical predictions and experimental validations

Electrocatalytic hydrogenation (ECH) represents a promising alternative to conventional hydrogenation techniques with high-pressure H 2 as a reductant. The proton-donating motif is an important factor governing the reaction efficiency but is usually overlooked in the ECH process. Herein, on the basis of density functional theory (DFT) predictions and experimental validations, we demonstrate that proton-buffer salts such as phosphate, carbonate and borate can greatly promote ECH efficiency. The DFT results predict that the buffer species can outperform water in donating protons for *C O hydrogenation into *C-OH via the Langmuir-Hinshelwood or proton-coupled electron transfer (PCET) mechanism, thus promoting the hydrogenation of carbonyl compounds. The experimental results demonstrate that with the buffer-promoting effects, 5-hydroxymethylfurfural (HMF) can be effectively converted at an efficiency of 96 % into the value-added 2,5-dihydroxymethylfuran (DHMF) with a yield of 80 % over cobalt oxide (Co 3 O 4 ) nanoarray catalysts under near-neutral buffer electrolyte. In situ Raman analysis and kinetic isotope experimental results reveal that the real mechanism is a combined Langmuir-Hinshelwood and PCET process. Such a buffer-promoting strategy also exhibits wide applicability in ECH of various other carbonyl compounds with different electrode catalysts. This work may provide a deep understanding of the ECH process and open up new opportunities to design effective systems for the conversion of HMF into value-added products. • Buffers could promote the ECH of 5-HMF over the Co 3 O 4 nanosheet arrays. • The yields of DHMF in buffers are much higher than that in non-buffered Na 2 SO 4 . • A combined L-H and PCET mechanism was proposed for the buffers promoting effect. • The buffer promoting effect was demonstrated a wide range of effectiveness.

Highly ordered mesoporous MnOx catalyst for the NH3-SCR of NOx at low temperatures

MnO x catalysts with 3D structure (Mn-HT) were prepared by hard-template method using KIT-6 as a template, and the catalytic performance for the selective catalytic reduction of NO x by NH 3 (NH 3 -SCR) at low temperatures was investigated. The template KIT-6 prepared by the different hydrothermal temperatures can exert significant effect on the catalytic performance of Mn-HT catalysts. Among the Mn-HT catalyst, the catalyst prepared using the template obtained at the hydrothermal temperature of 140 °C (Mn-140) exhibited the highest catalytic performance. Characterizations showed that Mn-140 catalyst possesses high reducibility with abundant surface oxygen species and Mn 4+ species. NH 3 -TPD and in situ DRIFTS demonstrated that there are more Lewis acid sites and Brønsted acid sites on the surface of Mn-140 catalyst, both of which would promote the adsorption and activation of NH 3 , leading to the reduction of NO x efficiently to proceed mainly by the Eley-Rideal(E-R) mechanism, accompanied by the Langmuir-Hinshelwood (L-H) mechanism. • MnO x with 3D structure was fabricated by hard-template method using KIT-6 template. • MnOx using the template obtained at hydrothermal temperature of 140 °C is the most active. • High redox property and abundant acid sites contribute to the high SCR activity. • The NH 3 -SCR over MnOx proceed by the E-R reaction mechanism.

Facet dependence of electrocatalytic furfural hydrogenation on palladium nanocrystals

Electrocatalytic hydrogenation (ECH) offers a sustainable route for the conversion of biomass-derived feedstocks under ambient conditions; however, an atomic-level understanding of the catalytic mechanism based on heterogeneous electrodes is lacking. To gain insights into the relation between electrocatalysis and the catalyst surface configuration, herein, the facet dependence of the ECH of furfural (FAL) is investigated on models of nanostructured Pd cubes, rhombic dodecahedrons, and octahedrons, which are predominantly enclosed by {100}, {110}, and {111} facets, respectively. The facet-dependent specific activity to afford furfuryl alcohol (FOL) follows the order of {111}>{100}>{110}. Experimental and theoretical kinetic analyses confirmed the occurrence of a competitive adsorption Langmuir-Hinshelwood mechanism on Pd, in which the ECH activity can be correlated with the difference between the binding energies of chemisorbed H (*H) and FAL (*FAL) based on density functional theoretical (DFT) calculations. Among the three facets, Pd{111} exhibiting the strongest *H but the weakest *FAL showed the copresence of the *H and *FAL intermediates on the Pd surface for subsequent hydrogenation, experimentally confirming its high ECH activity and Faradaic efficiency. The free energies determined using DFT calculations indicated that *H addition to the carbonyl of FAL on Pd{111} was thermodynamically preferred over desorption to gaseous H 2 , contributing to efficient ECH to afford FOL at the expense of H 2 evolution. The obtained insights into the facet-dependent ECH underline that surface bindings assist ECH or H 2 evolution considering their competitiveness. These findings are expected to deepen the fundamental understanding of electrochemical refinery and broaden the scope of electrocatalyst exploration. The facet dependence of electrocatalytic furfural hydrogenation is demonstrated on Pd nanocrystals and can be correlated with the difference between the binding energies of chemisorbed hydrogen and furfural based on a competitive adsorption Langmuir-Hinshelwood mechanism.

Influence of carbon deposits on Fe-carbide for the Fischer-Tropsch reaction

• Carbon removal rate-limiting for Fe-carbide in the Fischer-Tropsch (FT) reaction. • C deposits decrease FT activity and increase CH 4 selectivity. • SSITKA investigations used as function of amount of C deposits. • Slow sites mainly responsible for CH 4 formation via MvK mechanism. • Higher H 2 /CO ratio or total pressure removes C deposits and decreases deactivation. A well-known observation in the Fe-catalyzed Fischer-Tropsch (FT) reaction is that Fe-carbide catalysts deactivate due to carbon deposition. In comparison, the influence of such carbon deposits on the product distribution has been less widely reported. The present work investigates the relationship between the kinetics of the FT reaction for a carburized Raney-Fe model catalyst and the composition of the catalytic surface with a focus on carbon deposits. The deposition of carbon during the ongoing FT reaction at low pressure decreases the FT activity and increases the CH 4 selectivity. Steady-state transient isotopic kinetic analysis (SSITKA) at low pressure shows that the buildup of C deposits affects fast CO conversion sites on the Fe-carbide surface, mainly responsible for C-C coupling via a Langmuir-Hinshelwood mechanism, more than slow sites that mainly produce CH 4 via a Mars-Van Krevelen mechanism. Hindrance of migration of chain-growth monomers by C deposits decreases the amount of longer hydrocarbons. Nevertheless, SSITKA shows that C 2 products form faster, which is likely since their formation increasingly depends on monomers formed at proximate CO dissociation sites when the amount of carbon deposits increases. Carbon deposition can be suppressed and reversed by increasing the H 2 /CO ratio at constant pressure or by increasing the total pressure at constant H 2 /CO ratio. As such, the FT performance can be stabilized by operating at elevated pressure, even if initially the reaction was started at low pressure. Nevertheless, prolonged operation at low pressure leads to a less reactive character of the C deposits that cannot be removed anymore during high-pressure operation.

Bimetallic MnO2-supported catalysts for selective reduction of NO with NH3. Operando IR studies

• The promotion with CeO x lead to an improvement in catalytic activity. • MnCe showed a higher O α concentration which promotes the oxidation of NO to NO 2. • The higher catalytic activity of Ce promoted catalyst may be related to its capacity to adsorb NO x even in presence of water. • The incorporation of FeO x decreased NO x conversion in presence of water. Bimetallic shaped catalysts were prepared by wet equilibrium impregnation. MnO 2 was the main component and a second metal oxide (Co, Fe and Ce oxides) was added. The highest catalytic activity in the selective reduction of NO x with NH 3 of the Ce-promoted catalyst (88% of NO was converted at 170 °C) may be related to its capacity to adsorb NO x even in presence of water. It is demonstrated that NO adsorbs and oxidizes on CeO x and MnO x and then reacts with NH 3 via a Langmuir-Hinshelwood mechanism. However, in presence of water, the surface of Fe-promoted catalyst during NH 3 -SCR was only covered by NH 3 adsorbed species and NO x conversion was lower (65% of NO was converted at 170 °C). NO x adsorbed species were not observed, which suggests that the reaction of ammonia with gaseous NO x was much faster than that of nitrites/nitrates formation. Elay-Riedel seems to be the predominant mechanism over this catalyst.

Elimination of Indoor Volatile Organic Compounds on Au/SBA-15 Catalysts: Insights into the Nature, Size, and Dispersion of the Active Sites and Reaction Mechanism

Gold catalysts, with different particle sizes ranging from 19 to 556 Å, and supported on SBA-15 mesoporous silica, were prepared by using deposition-precipitation, co-precipitation, and impregnation methods. All samples were characterised by TEM, EXAFS, XPS, XRD, CFR (Continuous Flow Reactor), and TPR. The sample which proved to have the highest activity was characterised by TAP (Temporal Analysis of Products) as well. XPS, wide-angle XRD, EXAFS, and H2-TPR measurements and data analysis confirmed that gold was present as Au0 only on all samples. The size of the Au nanoparticle was determined from TEM measurements and confirmed through wide-angle XRD measurements. EXAFS measurements showed that as the Au-Au coordination number decreased the Au-Au bond length decreased. TEM data analysis revealed a dispersion range from 58% (for the smallest particle size) to 2% (for the highest particle size). For Au particles’ sized lower that 60 Å, the Au dispersion was determined using a literature correlation between the dispersion and EXAFS Au-Au coordination number, and was in good agreement with the dispersion data obtained from TEM. The Au dispersion decreased as the particle size increased. CFR experiments validated the relationship between the size of the gold particles in a sample and the sample’s catalytic activity towards acetone oxidation. The lowest temperature for the acetone 100% conversion, i.e., 250 °C, was observed over the reduced catalyst sample with the smallest particle size. This sample not only showed the highest catalytic activity towards acetone conversion, but, at the same time, showed high reaction stability, as catalyst lifetime tests, performed for 25 h in a CFR at 270 °C for the as-synthesised sample, and at 220 °C for the reduced sample, have confirmed. TAP (Temporal Analysis of Products) measurements and data analysis confirmed a weak competitive adsorption of acetone and oxygen over the Au/SBA-15 sample. Based on TAP data, a combination of Eley–Rideal and Langmuir–Hinshelwood mechanisms for acetone complete oxidation was proposed.

Synthesis of novel Co(3-x)MnxO4@TiO2 core-shell catalyst for low-temperature NH3-SCR of NOx with enhanced SO2 tolerance

In this study, the Co (3-x) Mn x O 4 @TiO 2 core-shell catalysts prepared by sol-gel and external kinetic coating method were investigated for DeNO x by response surface methodology (RSM) using 3-factor with 5-level experiments. Compared with CoMn 2 O 4 sample, the CoMn 2 O 4 @TiO 2 catalyst was optimized to obtain almost 100% NO x conversion at 125°C to 225°C that also maintained above 80% SCR activity with 100 ppm SO 2 and 10 vol.% H 2 O in the testing time within 24 h. The XRD and Raman show a clear distinction of that CoMn 2 O 4 spinel phase was well-dispersed on anatase TiO 2 over CoMn 2 O 4 @TiO 2 catalyst, which exhibited a core-shell structure with obvious distribution boundary of CoMn 2 O 4 core coated by TiO 2 shell confirmed by TEM images. This intact catalyst presented complete TiO 2 coating structure due to the detected bonds Mn-O, Co-O and particular Ti-O via FT-IR analysis. NH 3 -TPD and H 2 -TPR profiles indicated that the CoMn 2 O 4 @TiO 2 catalyst owned more acid sites, stronger acidity and enhanced redox capacities benefiting from its core-shell structure after TiO 2 coating. According to XPS analysis, higher content of (Mn 3+ +Mn 4+ )/(Mn 2+ +Mn 3+ +Mn 4+ ) (77.7%), Co 3+ / (Co 2+ + Co 3+ ) (53.5%) and surface oxygen (26.1%) were in favour of valence electron interaction (Mn 4+ +Co 2+ ↔Mn 3+ + Co 3+ , Mn 3+ +Ti 4+ ↔Mn 4+ + Ti 3+ ). The NH 3 -SCR reaction pathways over CoMn 2 O 4 and CoMn 2 O 4 @TiO 2 catalysts were compared and proposed through DRIFTS experiments, which mainly follows the typical Eley-Rideal (E-R) mechanism, while the Langmuir-Hinshelwood (L-H) mechanism is weak at 225°C. This study opens up a new avenue for designing efficient and environment-friendly NH 3 -SCR catalysts and looks promising for practical application.

The interaction mechanism of cesium with water on the SrTiO3(100) surface at room temperature

The interaction of water with cesium on the strontium titanate surface SrTiO3(100), was studied, mainly by means of work function measurements and thermal desorption spectroscopy. The catalytic role of cesium with respect to the dissociation of water on surface was investigated, by applying two different adsorption processes at room temperature (RT): (1) The adsorption of water on the cesium covered surface (sequential adsorption), and (2) the co-adsorption process (simultaneous adsorption) on surface. Based on the results and by adopting the Lewis acid–base model, we conclude that during the sequential adsorption the water molecules are mostly adsorbs non-dissociatively on surface, without oxidizing the alkaline overlayer. This seems to be due, first to the strong interaction between the alkaline adatoms and the substrate, and secondly to the limited maximum pre-deposited amount of cesium (≤ 0.45 ML). Instead, water dissociation appears to merely occur on defective sites of the substrate in accordance with previous studies. For a full cesium layer covered surface, the adsorbed water retracts the metallicity of cesium due to electrostatic interactions. In contrast to the sequential adsorption, during the co-adsorption process the oxidation of cesium takes place above a critical coverage of cesium (≥ 0.45 ML). It appears that the co-adsorbed cesium with water modifies the surface potential providing an effective template for cesium oxide, Cs2O development. Based on that, we suggest a catalytic reaction of water dissociation according to the Langmuir–Hinshelwood mechanism. Finally, we propose atomistic adsorption models for both processes of cesium with water adsorption.

A density functional theory study of the CO oxidation on Pt1 supported on PtX2 (X = S, Se, Te)

• Defective PtX 2 ( X = S, Se, Te) is an excellent structure for supporting Pt atom. • Pt 1 /PtTe 2 has high catalytic activity for CO oxidation. • The electronegativity of X atoms changes the O 2 capture ability of the substrate. • Defective monolayer TMDs can serve as excellent substrates for SACs. The geometric stability, electronic structure and catalytic properties towards CO oxidation of a single Pt atom supported on PtS 2 , PtSe 2 , PtTe 2 with a S, Se, and Te vacancies (Pt 1 /PtX 2 ) were systematically explored by density functional theory calculations. The results showed that the single Pt atom can be located at the vacancy site stably, providing accessible active sites for CO oxidation. Both the Langmuir-Hinshelwood (LH) mechanism and the termolecular Eley-Rideal (TER) mechanism were considered comprehensively. By comparing the rate-determining step (RDS) of CO oxidation process, we found that the LH mechanism is easier to achieve. Meanwhile, as the X atom changes from S to Te, the RDS energy barrier gradually decreases, which is attributed to promoted adsorption and activation of O 2 molecules on Pt 1 /PtX 2 . The results show that Pt 1 /PtTe 2 is the most active catalysts with a low RDS barrier of 0.41 eV. This work provides an important reference for the design of single atom catalysts (SACs) based on transition metal dichalcogenides (TMDs), and has profound implications for the use of supported SACs on defective TMDs for CO oxidation or other reactions.

Mechanism of iron doping promoting high temperature deNOx and anti-water vapor and SO2 poisoning of ZrW(Fe)Ox

• Z 1 W 0.2 F 0.007 was active for NH 3 -SCR of NO at 400–650 °C. • Fe doping improved activity of Z 1 W 0.2 F x for NH 3 -SCR of NO at 350–450 °C. • Fe doping enhanced anti-water vapor interference ability of Z 1 W 0.2 F 0.007 . • H 2 O promoted the Eley-Rideal deNO x reaction at high temperature. • H 2 O promoted deNO x activity and N 2 selectivity of Z 1 W 0.2 F 0.007 at above 450 ℃. Driven by the strategy of reducing pollution and CO 2 , high temperature deNO x catalyst has become a major demand for current gas-fired exhaust purification. A series of Fe-doped ZrWO x complex oxides (Z 1 W 0.2 F x ) were prepared by solution evaporation and co-firing method, and effects of Fe doping on their high-temperature deNO x activity, N 2 selectivity and anti-water vapor and SO 2 poisoning were mainly investigated and the promotion mechanism of Fe doping was analyzed and discussed. Results showed that Fe doping significantly improved NH 3 -SCR of NO over the Z 1 W 0.2 F x within 350–450 °C, mainly due to the redox properties of Fe 2 O 3 itself. Appropriate Fe doping increased specific surface area and enhanced surface acidity of Z 1 W 0.2 F x , the Z 1 W 0.2 F 0.007 possessed the optimal catalytic performance for deNO x , with NO conversion more than 90 % and N 2 selectivity more than 95 % at 400–650 °C. Moreover, compared to the blank sample of Z 1 W 0.2 , Fe doping remarkably enhanced anti-water vapor and SO 2 poisoning of Z 1 W 0.2 F x . Due to the competitive adsorption between H 2 O and NH 3 at low temperature, water vapor has a slight influence on deNO x activity at 400 °C. Interestingly, water vapor notably improved deNO x activity and N 2 selectivity at above 450 °C, because water vapor promoted the formation of hydroxyl groups and thus accelerated the Eley-Rideal deNO x at high temperature. SO 2 had no influence on the deNO x performance of Z 1 W 0.2 F x . Furthermore, both Lewis and Bronsted acid sites coexisted on the surface of Z 1 W 0.2 F x , and the NH 3 -SCR of NO over Z 1 W 0.2 F x at high temperature followed both Langmuir-Hinshelwood and Eley-Rideal reaction mechanisms.

Phosphotungstic Acid-Modified MnOx for Selective Catalytic Reduction of NOx with NH3

H3PW12O40-modified MnOx catalysts (denoted as Mn-HPW) were used for NOx elimination with co-fed NH3. The optimal Mn-HPW0.02 catalyst exhibited over 90% NOx conversion at 90–270 °C. The incorporation of HPW increased the amount of Lewis acid sites of the catalyst for adsorbing NH3, and accelerated the reaction between the adsorbed NH3 species and gas-phase NOx, thus, increasing the low-temperature catalytic activity. The oxidation ability of the Mn catalyst was decreased due to the addition of HPW, thus, mitigating the overoxidation of the adsorbed NH3 species and improving the de-NOx activity and N2 selectivity in the high-temperature region. DRIFT results revealed that the NH3 species on Lewis and Brønsted acid sites, bridged nitrate, and bidentate nitrate were important species/intermediates for the reaction. NH3-SCR over the Mn and Mn-HPW0.02 catalysts obeyed the Eley–Rideal and Langmuir–Hinshelwood mechanisms, simultaneously, at 120 °C.

A Density Functional Theory and Microkinetic Study of Acetylene Partial Oxidation on the Perfect and Defective Cu2O (111) Surface Models.

The catalytic removal of C2H2 by Cu2O was studied by investigating the adsorption and partial oxidation mechanism of C2H2 on both perfect (stoichiometric) and CuCUS-defective Cu2O (111) surface models using density functional theory calculations. The chemisorption of C2H2 on perfect and defective surface models needs to overcome the energy barrier of 0.70 and 0.81 eV at 0 K. The direct decomposition of C2H2 on both surface models is energy demanding with the energy barrier of 1.92 and 1.62 eV for the perfect and defective surface models, respectively. The H-abstractions of the chemisorbed C2H2 by a series of radicals including H, OH, HO2, CH3, O, and O2 following the Langmuir–Hinshelwood mechanism have been compared. On the perfect Cu2O (111) surface model, the activity order of the adsorbed radicals toward H-abstraction of C2H2 is: OH > O2 > HO2 > O > CH3 > H, while on the defective Cu2O (111) surface model, the activity follows the sequence: O > OH > O2 > HO2 > H > CH3. The CuCUS defect could remarkably facilitate the H-abstraction of C2H2 by O2. The partial oxidation of C2H2 on the Cu2O (111) surface model tends to proceed with the chemisorption process and the following H-abstraction process rather than the direct decomposition process. The reaction of C2H2 H-abstraction by O2 dictates the C2H2 overall reaction rate on the perfect Cu2O (111) surface model and the chemisorption of C2H2 is the rate-determining step on the defective Cu2O (111) surface model. The results of this work could benefit the understanding of the C2H2 reaction on the Cu2O (111) surface and future heterogeneous modeling.

Superior PbO-resistance of CeO2/ZrO2 catalyst promoted by solid superacid SO42−/ZrO2 for selective catalytic reduction of NOx with NH3

• ZrO 2 /SO 4 2− enhanced catalytic activity and resistance to PbO over CeO 2 /ZrO 2 catalyst. • ZrO 2 /SO 4 2− doping increased surface acidity, Ce 3+ /(Ce 3+ + Ce 4+ ) ratio and surface adsorbed oxygen. • Surface acid sites and active sites of CeO 2 /ZrO 2 -S catalyst were protected by ZrO 2 /SO 4 2− from PbO damage. • Mechanism model of PbO poisoning over CeO 2 /ZrO 2 and CeO 2 /ZrO 2 -S catalysts was proposed. The serious deactivation of denitration catalysts caused by heavy metals still a thorny issue in the practical application of selective catalytic reduction of NO x with NH 3 . Herein, we proposed a novel anti-poisoning strategy by designing SO 4 2− /ZrO 2 superacid supported CeO 2 /ZrO 2 catalyst, and the effect of SO 4 2− /ZrO 2 supported CeO 2 /ZrO 2 for PbO-resistance NO x catalytic reduction was investigated. It was worthy to note that the introduction of solid superacid SO 4 2− /ZrO 2 significantly enhanced catalytic performance over the entire temperature range, with an exceptionally high NO x removal efficiency over 98 % during 250–500 °C. When 2 wt% PbO was deposited on the fresh catalyst, the catalytic activity of CeO 2 /ZrO 2 catalyst decreased obviously, while CeO 2 /ZrO 2 -S catalyst can still maintain a higher NO x conversion over 90 % from 275 to 500 °C. The characterization results confirmed that the introduction of solid superacid SO 4 2− /ZrO 2 enhanced the surface acidity and promoted the transformation from Ce 4+ to Ce 3+ . The results of in situ DRIFTS implied that the Eley-Rideal (E-R) mechanism was obeyed over CeO 2 /ZrO 2 catalyst, and both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms were followed over CeO 2 /ZrO 2 -S catalyst in the SCR process. With regard to poisoned catalysts, the NH 3 adsorption was inhibited to some extent, while the reaction mechanism wasn’t changed by PbO poisoning.

Synthesis of p-n NiO-ZnO heterojunction for photodegradation of crystal violet dye

Photocatalytic treatment of wastewater utilizing oxides of metals as photocatalysts has merged a subject of major concern. The photocatalytic efficiency can be increased by the separation of electrons and holes formed by the absorption of photons. The development of heterojunction between two semiconductors is one of the methods used for the separation of photo-induced electrons and holes. Herein, we report a p-n NiO-ZnO heterojunction photocatalyst for efficient photodegradation of crystal violet dye. The homogeneous precipitation method was used for the synthesis of p-n NiO-ZnO in this study. The synthesized heterojunction was characterized by XRD, SEM, EDX, and TGA techniques. The aqueous solution of crystal violet dye was used as model wastewater for the evaluation of the photocatalytic efficiency of as-synthesized material. The photocatalytic performance of p-n NiO-ZnO for photodegradation of crystal violet dye was significantly higher than pristine NiO and ZnO. The photocatalytic activities of NiO, ZnO and NiO-ZnO were found in the ratio of 1: 3.8: 7.8, respectively. Similarly, the ratio of photocatalytic activities of 5% NiO-ZnO, 10% NiO-ZnO, and 15% NiO-ZnO was 1: 1.2: 0.8, respectively. The degradation data was analyzed for kinetics analyses using the Langmuir-Hinshelwood mechanism.