Chemisorption Of NO Research Articles

Adsorption of NO2 and subsequent formation of nitrate species in the dark on TiO2 nanoparticles exhibiting different morphologies: An in-situ FTIR study

Nitrogen oxides (NOx) are among the major air pollutants, which are responsible for the photochemical smog and haze formation and can cause acid rain. The selective catalytic reduction (SCR) process is a promising method to control the NOx emission from various stationery and mobile resources. The chemisorption of NO2 is regarded as the crucial step in this heterogeneous catalytic process. Here, the adsorption and formation of nitrate species on TiO2 nanoparticles (NPs) with different morphologies, designated as TiO2 trigonal, TiO2 nanowires, TiO2 nanocubes was examined in the dark using an in-situ FTIR spectroscopy, under NO2 as the feeding gas. The N2O4 formation is the initial step as soon as TiO2 NPs are subjected to NO2 adsorption, that is simultaneously transformed into other nitrate species via intramolecular disproportionation reaction. However, TiO2 NPs with different morphologies displayed a distinguished trend towards the stability and formation of various nitrate species. In particular, formation of NO+ was noticed only in TiO2 nanowires and TiO2 nanocubes (10mL_HF/40 h). Also, NO2 was detected in TiO2 trigonal shaped NPs, TiO2 nanocubes (4mL_HF/24 h), and TiO2 nanocubes (10mL_HF/24 h). The formation of different NO3- species, including monodentate, bidentate, and bridged NO3- (m-, b-, br-NO3-) were also observed. This study provides valuable information to modify the TiO2-based supports for the selective catalytic reduction technology.

Reduction of NO on chemically doped, metal-free graphene

The dissociation of NO on metal-free graphene was studied using density functional theory (DFT). The effect of heteroatomic substitution of boron and nitrogen on the activity of the single vacancy was explored. While the doping did not affect the NO chemisorption barrier, it was found that the dissociation step (with a barrier height of 260 meV) was activated by B (reducing the barrier down to 4 meV) but deactivated by N (up to 2.42 eV). In addition to the nature of the dopant, the location of the heteroatom with respect to the single vacancy site had an even stronger influence on the reactivity of graphene, reducing the barrier for dissociation fourfold.

Molecular insights into the role of char-bound hydrogen in char-NO reactions under high pressures: A reactive molecular dynamics simulation study

In the present work, the role of char-bound hydrogen in char-NO reaction under pressurized oxy-fuel combustion (POFC) conditions was studied using the reactive molecular dynamics (ReaxFF MD) simulations. The effects of char-bound hydrogen on the chemisorption of NO, formation of N2, kinetics of char-NO reaction, and structure of char at different pressures and temperatures were investigated. The results show that the char-bound hydrogen hindered the chemisorption of NO, and inhibited the generation of CN. The role of char-bound hydrogen in the chemisorption of NO weakened with the increase in pressure. Considerable amount of H2O was generated during the reaction of NO with H-containing char, which proves that char-bound hydrogen provided another channel for the conversion of NO to N2, especially at high pressures. The activation energies of the chemisorption of NO and the formation of N2 during the reaction of NO with H-containing char were determined to be 174 and 126 kJ/mol, respectively. The ReaxFF MD simulation results were in good agreement with previous experimental and DFT values. The char-bound hydrogen increased the activation energies of the chemisorption of NO and the formation of N2 by 40% and 29%, respectively. The role of char-bound hydrogen in char gasification and char structure were also examined. The char-bound hydrogen reduced the consumption of char, and CO was the main product from char gasification. The results of the O/C and N/C ratios of char indicate that char-bound hydrogen had little effect on the desorption of CO. By analyzing the dynamic evolution of char structure, it is found that char-bound hydrogen inhibited N-down chemisorption of NO.

Bimetallic metal organic framework-templated synthesis of a Cu-ZnO/Al2O3 catalyst with superior methanol selectivity for CO2 hydrogenation

It is highly desirable to develop inexpensive and highly selective catalyst for CO2 hydrogenation to methanol and Cu/ZnO/Al2O3 is a promising formulation. Herein, we report the design and synthesis of a Cu-ZnO/Al2O3 catalyst via a bimetallic metal organic framework (MOF)-templated strategy (termed Cu-ZnOMOF⊂Al2O3) and shed light on the role of the Cu-Zn@MOF precursor in this system for methanol synthesis. The developed Cu-ZnOMOF⊂Al2O3 exhibited high methanol selectivity (86.9%) and methanol space-time yield (407.2 gMeOH•kgcat−1•h−1) at higher CO2 conversion (9.1%) in comparison with the conventional Cu-ZnONO3/Al2O3 catalyst (79.6% and 209.0 gMeOH•kgcat−1•h−1, and 5.1%, respectively) at 240 ºC under 3.0 MPa. Spectroscopic characterization (TEM, XPS, EDX, in-situ DRIFTS) coupled with N2O chemisorption and temperature-programmed desorption of CO2 and H2 revealed that the surface of the new Cu-ZnOMOF⊂Al2O3 catalyst possesses higher Cu dispersion, surface-enriched ZnO and more Cu-ZnO interfacial sites, which leads to higher capability for CO2 and H2 adsorption and activation. These are considered to be the origin of higher methanol selectivity and enhanced activity of the catalyst prepared by the MOF-templated strategy for CO2 hydrogenation. This work offers a novel approach to optimizing Cu-ZnO/Al2O3 catalyst for CO2 hydrogenation to methanol.

Glycerol Valorization over ZrO2-Supported Copper Nanoparticles Catalysts Prepared by Chemical Reduction Method

Copper nanoparticles (NPs) and ZrO2-supported copper NPs (Cu NPs/ZrO2) were synthesized via a chemical reduction method applying different pH (4, 7 and 9) and evaluated in a glycerol dehydration reaction. Copper NPs were characterized with transmission electron microscopy (TEM) and UV–vis spectroscopy. Transmission electron microcopy (TEM) results revealed a homogeneous distribution of copper NPs. A hypsochromic shift was identified with UV–vis spectroscopy as the pH of the synthesis increased from pH = 4 to pH = 9. Zirconia-supported copper NPs catalysts were characterized using N2 physisorption, X-ray diffraction (XRD), TEM, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (NH3-TPD) and N2O chemisorption. The presence of ZrO2 in the chemical reduction method confirmed the dispersion of the copper nanoparticles. X-ray diffraction indicated only the presence of tetragonal zirconia patterns in the catalysts. XPS identified the Cu/Zr surface atomic ratio of the catalysts. TPR patterns showed two main peaks for the Cu NPS/ZrO2 pH = 9 catalyst; the first peak between 125 and 180 °C (region I) was ascribed to more dispersed copper species, and the second one between 180 and 250 °C (region II) was assigned to bulk CuO. The catalysts prepared at pH = 4 and pH = 7 only revealed reduction at lower temperatures (region I). Copper dispersion was determined by N2O chemisorption. With NH3-TPD it was found that Cu NPs/ZrO2 pH = 9 exhibited the highest total quantity of acidic sites and the highest apparent kinetic constant, with a value of 0.004 min−1. The different pH applied to the synthesis media of the copper nanoparticles determined the resultant copper dispersion on the ZrO2 support, providing active domains for glycerol conversion.

High-performance Cu/ZnO/Al2O3 catalysts for methanol steam reforming with enhanced Cu-ZnO synergy effect via magnesium assisted strategy

Methanol steam reforming (MSR) is an attractive approach to produce hydrogen for fuel cells. Due to the limited catalyst loading volume and frequent start-ups and shut-downs on board, it is highly desired to develop an extremely active and robust catalyst. Herein, on the basis of industrial Cu/ZnO/Al2O3 catalysts, a series of CuZnAl-xMg catalysts with enhanced Cu-ZnO synergy were synthesized via magnesium assisted strategy. The incorporation of magnesium was found to be beneficial to the enhancement of catalytic activity and stability of catalyst. A combination of complementary characterizations (e.g. XRD, H2-TPR, N2O chemisorption, TEM, XPS analysis etc.) proves that isomorphous substitution of Cu2+ in malachite phase gives rise to more dispersive Cu and ZnO NPs, and the increased Cu+/Cu0 ratio indicates the strengthened Cu-ZnO synergy effect, which leads to the boosted stability during the thermal treatment.

Modeling the Conductivity Response to NO2 Gas of Films Based on MWCNT Networks.

This work proposes a model describing the dynamic behavior of sensing films based on functionalized MWCNT networks in terms of conductivity when exposed to time-variable concentrations of NO2 and operating with variable working temperatures. To test the proposed model, disordered networks of MWCNTs functionalized with COOH and Au nanoparticles were exploited. The model is derived from theoretical descriptions of the electronic transport in the nanotube network, of the NO2 chemisorption reaction and of the interaction of these two phenomena. The model is numerically implemented and then identified by estimating all the chemical/physical quantities involved and acting as parameters, through a model fitting procedure. Satisfactory results were obtained in the fitting process, and the identified model was used to further the analysis of the MWCNT sensing in dynamical conditions.

Rh-Doped ZnO Monolayer as a Potential Gas Sensor for Air Decomposed Species in a Ring Main Unit: A First-Principles Study.

Using the first-principles theory, this paper studies the Rh-doping behavior on the ZnO monolayer and investigates the adsorption and sensing behaviors of a Rh-doped ZnO (Rh–ZnO) monolayer to NO2 and O3 to explore its potential as a gas sensor to evaluate the operation status of the ring main unit in the power system. The results indicate that the Rh dopant can be stably anchored on the TO site of the ZnO monolayer with an Eb of −2.11 eV. The Rh–ZnO monolayer shows chemisorption of NO2 and O3, with Ead values of −2.11 and −1.35 eV, respectively. Then, the electronic behavior of the Rh–ZnO monolayer before and after gas adsorption is analyzed in detail to uncover the sensing mechanism for gas detection. Our findings indicate that the Rh–ZnO monolayer is a promising resistance-type gas sensor with a higher response to O3 and can be explored as a field-effect gas sensor with a higher response to NO2. Our theoretical calculations provide the basic sensing mechanism of the Rh–ZnO monolayer for gas detection and would be meaningful to explore novel sensing materials for gas detection in the field of electrical engineering.

Oxygen effect in NO direct decomposition over K/Co-Mg-Mn-Al mixed oxide catalyst–Temperature programmed desorption study

• The role of oxygen in NO decomposition was studied over Co-Mg-Mn-Al mixed oxide. • Transition metals in octahedral coordination represent sites for NO chemisorption. • Potassium ensures NO oxidation to surface nitrite intermediates. • Oxygen inhibition was ascribed to formation of stable surface nitrate species. Co-Mg-Mn-Al mixed oxide with or without K was prepared and characterized by XPS, TPR H 2 , TPD NO, TPD O 2 and TPD NO+O 2 . NO decomposition was performed over catalyst activated in different atmosphere (N 2 , He, O 2 ). Presence of oxygen during activation changed the course of surface stabilization but did not affect NO conversion achieved at steady state. O 2 desorbed as a reaction product does not affect the reaction rate for NO inlet concentration of 400 - 8000 ppm, but presence of O 2 in inlet gas mixture (0.05 - 3 mol.%) has significant inhibiting effect. Transition metals in octahedral coordination represent sites for NO chemisorption, while potassium ensures NO oxidation to surface nitrites, which are indispensable reactive species. Oxygen desorption was the slowest reaction step, while N 2 desorption was fast. Oxygen inhibition was ascribed to oxidation of NO* species on the octahedral Co 3+ and Mn 3+ to more stable surface nitrates making NO* species as limiting reactant.

The correlation of NO chemisorption adsorption with its directly catalytic dissociation pathway on β-MnO2(1 1 0) and (1 0 1) surfaces

MnO2-based oxide catalysts have recently drawn so much attention owing to its good catalytic activity for NOx direct catalytic decomposition at low-temperature. As the reaction mechanism of NO direct catalytic decomposition on different MnO2 surfaces is not yet clear, it is important to understand the influence of different crystal surfaces of β-MnO2 on catalytic activity for NO decomposition. The correlation of NO chemisorption with its dissociation pathways on β-MnO2(110) and (101) surfaces are investigated based on density functional theory (DFT) with Vienna Ab-initio Simulation Package (VASP). The calculation results have shown that NO prefers to be adsorbed on β-MnO2(110) instead of β-MnO2(101) surface. The analysis results of density of states and differential charge density indicate that the interaction between NO and β-MnO2(110) surface is stronger and the adsorbed NO had more charge transfer with β-MnO2(110) surface. The effective activation energies of the possible NO dissociation pathways on the β-MnO2(110) and (101) surfaces are 2.57 and 3.07 eV, respectively. The lower energy barrier on β-MnO2(110) must be associated with the bridge adsorption of NO and more electrons transfer from NO to the surface, which is conducive to the breaking of N-O bond.

Tuning the interfacial sites between copper and metal oxides (Zn, Zr, In) for CO2 hydrogenation to methanol

The influence of different metal oxides (ZnO, ZrO2, In2O3) in CO2 hydrogenation to methanol over Cu-based catalysts was studied. The catalysts were characterized using x-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), N2-physisorption, N2O chemisorption, H2 temperature-programmed reduction (H2-TPR), and CO2 temperature-programmed desorption (CO2-TPD). It was found that impregnating ZrO2 onto Cu/ZnO enhances the methanol formation rate from 14.7 mmol∙gcat−1∙h−1 to 15.6 mmol∙gcat−1∙h−1 (230 °C, 30 bar, 38 000 cm3/(gcat h)), which is attributed to the formation of Cu-ZrO2 sites. The results also indicate that In-doping of the Cu-based catalysts generates CuxIny alloys, which seems to inhibit the active sites on the Cu surface. However, new sites for methanol synthesis are present when Cu/ZrO2/In2O3 is prepared by co-precipitation. This is attributed to In-Zr mixed oxide species that increases the methanol formation rate from 53.2 mmol∙gcat−1∙h−1 to 60.5 mmol∙gcat−1∙h−1 (270 °C, 30 bar, 140 000 cm3/(gcat h)).

Influence of Water on Nitrous Oxide Adsorption and Desorption on Coals

Oxygen-enriched coal-combustion flue gas geologic sequestration in unmineable coal seams is a promising option to mitigate gaseous pollutant emissions and recover coalbed methane (CH4). Water (H2O) always exists in practical coal seams and shows significant impact on fluid adsorption, desorption, diffusion, and flow behaviors. Thus, this study mainly addressed the influence of H2O on nitrous oxide (N2O) adsorption and desorption, a typical component that existed in oxygen-enriched coal-combustion flue gas, on different rank coals. Results indicate that the N2O adsorption equilibrium and kinetic behaviors within moist coals can be well-predicted using the Sips model and the simplified bidisperse kinetic model, respectively. The H2O dramatically hinders the adsorption and diffusion capability of N2O within coals, which is attributed to the fact that H2O molecules occupy pore channels, induce coal matrix swelling, and compete with N2O molecules for the same adsorption sites, particularly the oxygen-containing functional groups. The H2O impairs the physisorption and chemisorption of N2O on coals. Furthermore, the H2O enhances the chemical transformation among the four main nitrogen-containing species within coals, that is, pyridine-N, pyrrole/pyridone-N, quaternary-N, and oxide-N. Particularly, the abundant −H groups of H2O molecules inhibit the decomposition of pyrrole/pyridone-N and accelerate the transformation of pyridine-N, while −OH groups of H2O molecules promote the formation of oxide-N. To sum up, the practical N2O geologic sequestration should focus on the effects of in-situ H2O within coal reservoirs.

CeO2 and TiO2 support material effects on NH3 decomposition pathway mechanism over Cu–Zn catalysts

The decomposition of NH3 over Cu–Zn catalysts, supported on ceria and titania, was investigated, producing carbon (di)oxide-free H2. The rate of the H2 formation at the exposed metallic Cu atoms (cumulative turnover frequency) for dispersed Cu–Zn depended strongly on the type of metal oxide support, indicating that the pathway active sites of Cu–Zn nano-catalysts were not identical in quantity. The investigation of the associative desorption process of atomic nitrogen moieties formed by the NH3 scission over Cu–Zn alloy revealed that N2 interface evolution temperature was affected by the nature of substrates. The characterization of the nanomaterials before the catalyzed splitting reactions of NH3 was carried out by XRD, N2 physisorption, N2O chemisorption, H2 TPD, CO2 TPD, NH3 TPD and H2 TPR. TEM and XPS were conducted on both fresh and used composites. Cu–Zn dispersion increased in the presence of TiO2. These spinel forms exhibited a strong Cu0.5Zn0.3Ti0.2O2–x (x = 0–1) structure interaction. Cu–Zn/CeO2 showed a 79% conversion of ammonia at 600 °C, whereas Cu–Zn/TiO2 demonstrated 63% at comparative operating conditions. A high catalytic activity, reflected in almost total consumption of ammonia at 700 °C with the hydrogen reactive production of 33.2 mmol g−1 min−1, was achieved over Cu–Zn/TiO2. No reactivity loss considering the NH3 depletion under applied reactor runs was detected, implying that materials had excellent time-on-stream stability. By scanning and transmission electron microscopy, bimetallic Cu–Zn was also observed, displaying a uniform TiO2 particle distribution on a structured sample surface. Impregnated zinc and copper species were uniformly distributed over Cu–Zn/TiO2. In the case of higher precursor content, a slight Cu domain agglomeration was noted. A heterogeneous mixed phase of Cu and Cu2O was present in all examined powders, as exposed by Cu L-edge spectra ratios.

CuPd bimetallic catalyst with high Cu/Pd ratio and its application in CO2 hydrogenation

The surface and catalytic properties Cu-Pd bimetallic catalyst with a high Cu/Pd ratio of 33.5 was investigated for the hydrogenation of CO2 and was compared with the corresponding monometallic catalysts. The catalysts were synthesized by the incipient-wetness impregnation method, characterized by N2-physisorption, XRD, TPR, CO pulse titration, N2O chemisorption, CO2-TPD, and FT-IR of adsorbed CO, and were evaluated in a fixed-bed reactor. The interaction between Cu and Pd results in a better dispersion of both Cu and Pd atoms and facilitates the reduction properties. Phase separation of Pd1Cu3 alloy and Cu appears over the bimetallic catalyst, while at some part of the catalysts, isolated Pd sites exist over the Cu-rich particles. Both geometric and electronic effects are present over the bimetallic catalyst. The catalytic performances are found to be similar over Cu/SiO2 and Cu-Pd/SiO2 when normalized to the surface Cu sites. Specifically, CuPd/SiO2 shows enhanced activity than Cu/SiO2 mainly due to the geometric effect, whereas the electronic effect is weak for the catalytic performance.

Manganese containing copper aluminate catalysts: Genesis of structures and active sites for hydrogenation of aldehydes

Copper aluminate spinel (CuO.CuAl2O4) is the favoured Cr-free substitute for the copper chromite catalyst (CuO.CuCr2O4) in the industrial hydrogenation of aldehydes. New insights in the catalytic mechanism were obtained by systematically studying the structure and activity of these catalysts including effects of manganese as a catalyst component. The hydrogenation of butyraldehyde to butanol was studied as a model reaction and the active structure was characterised using X-ray diffraction, temperature programmed reduction, N2O chemisorption, EXAFS and XANES, including in-situ investigations. The active catalyst is a reduced spinel lattice that is stabilised by protons, with copper metal nanoparticles grown upon its surface. Incorporation of Mn into the spinel lattice has a profound effect on the spinel structure. Mn stabilises the spinel towards reduction of CuII to Cu0 by occupation of tetrahedral sites with Mn cations, but also causes decreased catalytic activity. Structural data, combined with the effect on catalysis, indicate a predominantly interface-based reaction mechanism, involving both the spinel and copper nanoparticle surface in protonation and reduction of the aldehyde. The electron reservoir of the metallic copper particles is regenerated by the dissociative adsorption and oxidation of H2 on the metal surface. The generated protons are stored in the spinel phase, acting as proton reservoir. Cu(I) species located within the spinel and identified by XANES are probably not involved in the catalytic cycle.

Reaction of NO2 with Groups IV and VI Transition Metal Oxide Clusters.

The addition of NO2 to Group IV (MO2)n and Group VI (MO3)n (n = 1-3) nanoclusters was studied using both density functional theory (DFT) and coupled cluster theory (CCSD(T)). The structures and overall binding energetics were predicted for Lewis acid-base addition without transfer of spin (a physisorption-type process) and the formation of either cluster-ONO (HONO-like or bidentate bonding) or NO3- formation where for both the spin is transferred to the metal oxide clusters (a chemisorption-type process). Only chemisorption of NO2 is predicted to be thermodynamically allowed at temperatures ≥298 K for Group IV (MO2)n clusters with the formation of surface chemisorbed NO2 being by far the most energetically favorable. The ligand binding energies (LBEs) for physisorption and chemisorption on the TiO2 nanoclusters are consistent with computational studies of the bulk solids. Chemisorption is only predicted to occur for (CrO3)n clusters in the form of a terminal nitrate containing species whereas the larger chemisorbed nitrate structures for (MoO3)n and (WO3)n were found to be metastable and unlikely to form in any appreciable amount at temperatures of 298 K and higher. NO2 is predicted to only be capable of physisorbing to (MoO3)n and (WO3)n at lower temperatures and therefore unlikely to bind NO2 at temperatures ≥298 K. Correlations between the (MO3)nNO2 ligand bond energies and the chemical properties of the parent (MO3)n clusters (Lewis acidity, ionization potentials, excitation energies, and M = O/M-O bond strengths) are described.

Selective dehydration of glycerol on copper based catalysts

Glycerol is produced in large quantities as a byproduct of biodiesel, and among others hydroxyacetone (acetol) is an important commodity obtained from glycerol. Metallic Cu has been identified as active site for the dehydration of glycerol to hydroxyacetone and acid and metal sites are known to influence the catalytic performance. In this study, dehydration of glycerol over 5 wt.% copper supported on γ-Al2O3, ZrO2 and SiO2 was investigated. Catalysts were characterized by N2 physisorption, H2-TPR, NH3-TPD, N2O chemisorption, XPS, XRD, FTIR of pyridine adsorption. Cu/ZrO2 exhibited the highest hydroxyacetone yield at 20 % of glycerol conversion and the highest apparent reaction rate. The superior activity of Cu/ZrO2 was attributed to the highly acidic, both Lewis and Brönsted acidic, nature of the support and positive roles of the interfacial sites. The Weisz-Prater (WP) criterion was applied to confirm the absence of intraparticle diffusion limitations. It was assumed spherical particles and first order reaction. The WP value obtained in the worst scenario was less than 0.3 ensuring no diffusion limitation. Complementary DFT study indicates that both glycerol and hydroxyacetone interact significantly stronger on Cu/γ-Al2O3 and Cu/ZrO2 compared to metallic Cu, suggesting that the active sites are at the interface of Cu particles and the acidic support.

Environmental-friendly production of FeNbTi catalyst with significant enhancement in SCR activity and SO2 resistance for NOx removal

An environmental-friendly FeNbTi catalyst with different Nb doping was investigated for NH3-SCR reaction at low temperature, which exhibited excellent activity and tolerance to SO2 and H2O poisoning. A series of characterization were used to investigate the reasons for the high activity and SO2 resistance of the catalyst before and after Nb modification, such as BET, XRD, XPS, H2-TPR, O2-TPD, NH3-TPD, NO-TPD and DRIFT. XRD and XPS results displayed that the doping of Nb could promote the speciation transformation of Fe2O3 from crystalline to amorphous phase and more chemisorbed oxygen species generated. In addition, NH3-TPD and NO-TPD results suggested that the amount of surface acid sites and NO chemisorption increased after Nb doping, and the adsorption and oxidation of NH3 or NO improved through DRIFT analysis. All these factors contributed to the outstanding SCR performance and strong resistance to SO2 and H2O.

Cu1−xMgxAl3 spinel solid solution as a sustained release catalyst: One-pot green synthesis and catalytic performance in methanol steam reforming

A versatile and green method for the synthesis of an efficient catalyst applied in methanol steam reforming is promising in view of clean energy production. Cu1−xMgxAl3 ternary spinel oxide catalysts have been prepared by a one-pot solid-phase reaction method using Cu(OH)2, Al2O3·xH2O and MgCO3 as the raw materials. The structure, reducibility, surface chemical state, and the aluminum ion distribution are comprehensively characterized by XRD, UV–vis, XPS, H2-TPR, N2O chemisorption, and 27Al MAS NMR techniques. The performances of the catalysts in methanol steam reforming are evaluated. Compared with binary Cu-Al spinel, the incorporation of Mg into the spinel lattice results in the change of Al3+ cation distribution between tetrahedral and octahedral sites, and thus the variation of copper surrounding environment can be inferred. Consequently, the copper releasing rate from the Mg containing spinel structure declines substantially, which is believed to be in favor of maintaining a stable catalytic performance longer. Besides, the ternary spinel oxide might facilitate the in-situ formation of smaller nano copper metals compared to CuAl3 binary spinel catalyst. Among all the catalysts, Cu0.9Mg0.1Al3 presents the highest activity as well as the best catalytic stability. The findings of this report suggest that introducing a foreign cation into the Cu-Al spinel structure might be a promising way to regulate the copper releasing property for achieving a better sustained release catalyst system.

Synergetic Effect of Na–Ca for Enhanced Photocatalytic Performance in NOX Degradation by g-C3N4

Na–Ca co-doping modified g-C3N4 were prepared through the one pot thermal polymerization under a mixture consisting of melamine and sodium chloride-calcium chloride bi-component metal salt in different proportions. The photocatalytic NOX degradation performance of prepared samples were assessed by NOX toxicity. The results showed that the lowest NOX toxicity of co-doping modified g-C3N4 is 3.49 and 1.77 times than that of Na and Ca single-doping modified g-C3N4 when the weight ratio of melamine to metal salt was 1:0.3. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), N2 adsorption–desorption were used to characterize the crystalline structures and morphologies of products. Infrared spectrum analyzer (FT-IR), X-ray photoelectron spectroscopy (XPS) were used to study the effects of Na–Ca on the chemical composition of products. And the optical performance of products was characterized by ultraviolet–visible spectra (UV–Vis) and optical luminescence (PL). The results showed that Na–Ca co-doping had a synergic effect on NOX degradation. The larger surface area is equivalent to the increase of photocatalyst dosage. Sodium doping increases NO degradation efficiency by promoting redox capacity and the separation of electron-hole pairs, calcium doping can enhance the chemisorption of NO2 because of the generation of CaCO3 and thus reduce the emission of NO2.