Photocatalytic Reduction Of NO Research Articles

The efficient electrocatalytic and photocatalytic reduction of nitric oxide into ammonia over 0D/3D g-C3N4 quantum dots/3DOMM-TiO2-x heterojunction

An appealing strategy for air pollution treatment is the conversion of NOx in flue gas to valuable chemicals in ambient conditions. The electrocatalytic reduction of nitric oxide has been demonstrated to be a very effective process, however, the photocatalytic reduction of nitric oxide hasn't received much research attention. Herein, we developed a novel 0D/3D g-C3N4 QDs/3DOMM-TiO2-x catalyst, and investigated its performances in both electro- and photocatalytic reduction of nitric oxide to ammonia through experimental analysis and theoretical computation. In the electrocatalytic reduction of NO, the NH3 yield of g-C3N4 QDs/3DOMM-TiO2-x is up to 3841.5 μg h−1 mg−1, which is 15.15, 3.14, and 1.15 times that of TiO2 (P25), 3DOMM-TiO2 and g-C3N4 QDs/3DOMM-TiO2, respectively. The best reaction pathway is *NO → *HNO → *HNOH → *NH→ *NH2 → *NH3 → *NH4+, and the potential determining step is *NH → *NH2. Furthermore, the NH3 yield is estimated to be 95.07 μg h−1 mg−1 in the photocatalytic reduction of NO, using g-C3N4 QDs/3DOMM-TiO2-x as single photoelectrode. The NO molecules are reduced to NH3 on the CB of the g-C3N4 QDs by the accumulated photoelectrons, and charge migration occurs according to the S-scheme in the g-C3N4 QDs/3DOMM-TiO2-x photocatalyst. The results pave a new route for producing ammonia from NO under ambient conditions using electricity and solar energy.

Beyond Purification: Highly Efficient and Selective Conversion of NO into Ammonia by Coupling Continuous Absorption and Photoreduction under Ambient Conditions.

Although the selective catalytic reduction technology has been confirmed to be effective for nitrogen oxide (NOx) removal, green and sustainable NOx re-utilization under ambient conditions is still a great challenge. Herein, we develop an on-site system by coupling the continuous chemical absorption and photocatalytic reduction of NO in simulated flue gas (CNO = 500 ppm, GHSV = 18,000 h-1), which accomplishes an exceptional NO conversion into value-added ammonia with competitive conversion efficiency (89.05 ± 0.71%), ammonia production selectivity (95.58 ± 0.95%), and ammonia recovery efficiency (>90%) under ambient conditions. The anti-poisoning capacities, including the resistance against factors of H2O, SO2, and alkali/alkaline/heavy metals, are also achieved, which presents strong environmental practicability for treating NOx in flue gas. In addition, the critical roles of corresponding chemical absorption and catalytic reduction components are also revealed by in situ characterizations. The emerging strategy herein not only achieves a milestone efficiency for sustainable NO purification but also opens a new route for contaminant resourcing in the near future of carbon neutrality.

Development of La1−xCexFeO3/attapulgite nanocomposites for photocatalytic reduction of NO at low temperature

A series of attapulgite (ATP) supported perovskite-type La1−xCexFeO3 (x = 0–0.5) nanocomposites were synthesized by a facile sol–gel method. The samples were characterized by X-ray diffraction, Transmission electron microscope, Ultraviolet–visible spectroscopy and Fourier-transform infrared spectroscopy. The photoactivity of the La1−xCexFeO3/ATP was evaluated via catalytic reduction of NOx with NH3 at low-temperature under visible light irradiation. The impact of the doping fraction of Ce on the NOx conversion was investigated. Results show that ATP provides a high surface area facilitating the dispersion of small nanoparticles as well as the gas adsorption, while incorporation of an appropriate amount of Ce leads to the formation of coherent heterostructure La1−xCexFeO3/CeO2 which benefits the separation of electron–holes. The highest conversion rate of NO reaches 80% at low temperature when the doping amount is 0.3.

Photocatalytic reduction of NO with ethanol on Au/TiO2

The effect of illumination on the surface interaction and the reaction between NO+C2H5OH was investigated on Au/TiO2 catalyst. By means of Fourier transform infrared spectroscopy, the formation of absorption bands at ∼2180 and ∼2210cm−1 was observed. The first was attributed to the NCO species locating on Au particles, and the second one to NCO residing on the TiO2 support. While the thermal reaction between NO and C2H5OH on Au/TiO2 catalyst occurred with measurable rate only at and above 473–523K, illumination of the system induced the reaction even at room temperature. A fraction of NO was converted into N2O, another one to N2. At the same time, the photo-induced decomposition of C2H5OH also occurred yielding CH3CHO, H2, CO, and CH4. Interestingly, the presence of NO significantly slowed down the rate of the decomposition of C2H5OH. Separate studies revealed that all the products formed in the decomposition of C2H5OH reacted with NO. A mechanism for the photocatalytic reduction of NO with C2H5OH is proposed taking into account the effects of the products of C2H5OH photolysis. Incorporation of N into TiO2, which significantly lowered its band gap, appreciably enhanced the reduction of NO, which occurred even in visible light.

Effect of Vehicle Classification and Activity on Field Evaluation of Photocatalytic Concrete Pavements’ Ability to Remove Nitrogen Oxides – A Case Study

There has been an increasing interest in photocatalytic pavements, which can decompose pollutants to nonhazardous waste products with little energy requirements and selectivity. The objective of this study is to evaluate the effects of vehicle activity and classification on nitrogen oxide (NO_x) pollution emitted and correlating these factors to the NO_x reduction from photocatalytic pavements. To achieve this objective, a field study was conducted with 22.3 m^2 of photocatalytic spray coated area and 22.3 m^2 of uncoated control area. Evidence of photocatalytic reduction of NO_x was evaluated by directly measuring NO_x reductions from the ambient air. A traffic study was conducted for the photocatalytic control areas to characterize the variability in traffic classification and activity between the two areas and its effects on interpreting NO_x reduction. Results showed that the amount of NO_x emitted in the area predicted to be from traffic sources is no more than 5 grams per hour. Due to the low values of pollution emitted in the both the photocatalytic area and the control area, minor differences in traffic activity between these two areas resulted in significant differences in the amount of pollution emitted between the photocatalytic and the control areas. This may complicate the interpretation of the NO_x reduction results. Furthermore, there was no significant linear correlation of vehicle class and speed and NO_x reduction.

Preparation of high-aspect-ratio TiO2 nanotube arrays for the photocatalytic reduction of NO in air streams

The aim of this study is to fabricate TiO2 nanotubes arrays (TNTs) with smooth homogenous morphology by the anodization of titanium foil in fluorine-contained electrolytes. A series of materials analysis techniques, such as field-emission scanning electron microscopy, potentiostat/galvanostat and X-ray diffractometer, are used to characterize the surface morphology, phase formation, lattice parameters and the induced photocurrent intensity of TNTs. As the experimental results, the tube dimension of TNTs is found to be determined by the migration and diffusion of ions in the electrolyte corresponding to the concentration profiles of oxygen-containing anionic species and hydrogen ions within the TiO2 nanotubes. High-aspect-ratio TNTs with a superior degree of regularity and homogeneity are favored to be formed in the fluoride-contained ethylene glycol solutions due to the suppression of pH bursts and local ions concentration fluctuations during anodization in the highly viscous electrolytes. To compare the NO reduction by photo-SCR using spherical TiO2 (P25) and tubular TiO2, the performance of NO reduction by photo-SCR is significantly affected by the available surface area (active sites) of TiO2 rather than the crystal composition of TiO2.

FT-IR study of the reaction mechanisms for photocatalytic reduction of NO with CO promoted by various single-site photocatalysts

Photocatalytic reduction of NO with CO has been carried out using various single-site photocatalysts under UV-light irradiation. The single-site photocatalysts prepared by incorporating transition metal oxides within SiO2 (M/SiO2: MMo, V, and Cr) display different photocatalytic activities. Mo/SiO2 promotes photocatalytic reduction of NO with CO efficiently to produce N2 via the intermediate N2O. V/SiO2 was observed to promote the reaction that leads to selective production of N2O that does not undergo subsequent reduction to form N2. When Cr/SiO2 is used as the photocatalyst, reduction of NO does not take place. The results of Fourier transform infrared investigations reveal that differences in photocatalytic activities are due to different reactivity of reactants-adsorbed transition metal oxides in M/SiO2 and, consequently, the reaction mechanisms for the photocatalytic reduction of NO with CO over M/SiO2 are proposed.

A combined experimental and computational study on the adsorption and reactions of NO on rutile TiO2

In this work we combined computational density functional theory with experimental infrared spectroscopy to determine the adsorbate structure of NO and its reaction products N(2)O(2), N(2)O, and NO(2) on rutile TiO(2). These reactions are important for the photo-catalytic reduction of NO in exhaust gas, but yet little is known about the mechanisms or the intermediates involved. The combination of high-quality ultrahigh vacuum FTIRS data with large scale embedded cluster calculations using an accurate hybrid density functional rendered it possible to identify and assign unambiguously vibrational frequencies for nine species which are formed upon adsorption and reaction of NO on rutile TiO(2). Some of them have been observed for the first time. As a result of the quantum chemical calculations we can report for all adsorbates accurate structures and binding energies.

Selective reduction of NO by photo-SCR with ammonia in an annular fixed-film photoreactor

Gaseous NO was photocatalytically reduced at room temperature by photo-assisted selective catalytic reduction (photo-SCR) with ammonia over TiO2 in this study. NO reduction efficiency and N2 selectivity were determined from gases composition at the outlet stream of photoreactor. Effect of operating conditions, e.g. light intensity and inlet concentrations of ammonia and oxygen, on the NO reduction efficiency and N2 selectivity were discussed to determine the feasible operating condition for photocatalytic reduction of NO. Experimental results showed that selective catalytic reduction of NO with ammonia over TiO2 in the presence of oxygen was a spontaneous reaction in dark. The photoirradiation on the TiO2 surface caused remarkable photocatalytic reduction of NO to form N2, NO2, and N2O under 254 nm UV illuminations, while almost 90% of N2 selectivity was achieved in this study. The ammonia and oxygen molecules played the roles of reductant and oxidant for NO reduction and active sites regeneration, respectively. The reduction of NO was found to be increased with the increase of inlet ammonia and oxygen concentrations until specific concentrations because of the limited active sites on the surface of TiO2. The kinetic model proposed in this study can be used to reasonably describe the reaction mechanism of photo-SCR.

Photocatalytic Reduction of NO with Ethanol on Ag/TiO2

The effect of illumination on the surface interaction and the reaction between NO + C2H5OH was investigated on TiO2 and Ag/TiO2. By means of Fourier transform infrared spectroscopy the formation of an absorption band at 2,210 cm−1 was observed on pure TiO2, which was attributed to the NCO species. Similar measurements on Ag/TiO2 produced another spectral feature at 2,170 cm−1, which was assigned to the vibration of NCO bonded to Ag. These absorption bands formed more easily on oxidized than on reduced surfaces. Study of the catalytic reduction of NO with ethanol showed that the illumination of the system induced the reaction even at room temperature. Photo catalysis of NO + C2H5OH reaction on TiO2 (T R = 473 K) (A), 2% Ag/TiO2 (T R = 473 K) (B) and (T OX = 573 K) (C).

FTIR and TPD Analysis of Surface Species on a TiO2Photocatalyst Exposed to NO, CO, and NO−CO Mixtures: Effect of UV−Vis Light Irradiation

As a continuation of our previous work on the kinetics of photocatalytic reduction of NO by CO on titanium dioxide, interaction of a Degussa P-25 TiO2 photocatalyst with NO, CO, and NO−CO mixtures ...

Highly selective photocatalytic reduction of NO 2 in air to NO using Cu 2+-loaded TiO 2 thin films

We have discovered that Cu 2+-loaded TiO 2 films (1.5 μm thick) exhibit a high activity of selective reduction of NO 2 to NO in air under UV light illumination (1 mW cm −2). This effect is associated with a reduced NO oxidation to HNO 3. For an increasing amount of Cu 2+ ions the NO reductions become more stable. Cu 2+ ions are responsible for the high redox property, playing an important role in adsorption of NO 2/NO 2 −, electron transfer from the TiO 2 to NO 2/NO 2 −, and recombination center for positive holes.

Photocatalytic reduction of NO with NH 3 using Si-doped TiO 2 prepared by hydrothermal method

A series of Si-doped TiO 2 (Si/TiO 2) photocatalysts supported on woven glass fabric were prepared by hydrothermal method for photocatalytic reduction of NO with NH 3. The photocatalytic activity tests were carried out in a continuous Pyrex reactor with the flow rate of 2000 mL/min under UV irradiation (luminous flux: 1.1 × 10 4 lm, irradiated catalyst area: 160 cm 2). The photocatalysts were characterized by X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectrophotometer, transmission electron microscopy (TEM), photoluminescence (PL) and temperature-programmed desorption (TPD). The experiment results showed that NO conversion on Si/TiO 2 at 323 K could exceed 60%, which was about 50% higher than that on Degussa P25 and pure TiO 2. With the doping of Si, photocatalysts with smaller crystal size, larger surface area and larger pore volume were obtained. It was also found that Ti–O–Si bands were formed on the surface of Si/TiO 2 and that the surface hydroxyl concentration was greatly increased. As a result, total acidity and NH 3 chemisorption amount were enhanced for Si/TiO 2 leading to its photocatalytic activity improvement.

Photocatalytic Reduction of NO by CO on Titanium Dioxide under Visible Light Irradiation

It is shown for the first time that the photoassisted reduction of NO by CO into N2 and N2O can occur on TiO2 catalysts upon visible light irradiation (λ > 380 nm) at room temperature. The selectivity of photoreduction of NO into N2 reaches 90−95%. The CO2 formed which predominantly remains on the surface can be quantitatively desorbed after completion of the photoreaction by heating TiO2 to ∼500 K. The rates of NO consumption and product accumulation remain virtually constant upon successive admissions of the CO−NO mixture thus indicating a high stability of catalyst activity. It is found that the quantum yield of NO photoreduction by CO is considerably greater for visible light irradiation (λ = 405 + 436 nm) than for UV irradiation (λ = 365 nm). Experiments with 18O-enriched NO revealed that, under visible light irradiation, an intense oxygen isotopic exchange between NO and TiO2 develops. The photocatalytic reaction requires the presence in nonstoichiometric TiO2-x of electron-donor centers (Ti3+ ions, F and F+ centers) able to absorb visible light. A reaction mechanism is proposed which includes the following stages: (a) NO photoadsorption along two parallel routes, by e- capture from the electron-donor center by NO to yield adsorbed NO- species and by NO interaction with the hole O- to give adsorbed nitrite NO2-; (b) reduction of NO- into N2O and further into N2; and (c) photoreduction of adsorbed nitrite NO2- into N2O and further into N2 by CO which regenerates the donor centers. It is assumed that the photoinduced oxygen heteroexchange proceeds via adsorbed nitrite complexes.

Kinetics of Photocatalytic Reduction of NO by CO with Pd2+-Ion-Substituted Nano-TiO2

The objective of the present study is to develop the reaction mechanism and kinetics of photoreduction of NO by CO. For this purpose, the reactions were conducted in the presence of Pd-ion-substituted nano-TiO 2 , Ti 1-x Pd x O 2-δ , which was synthesized via a solution combustion method. The photocatalytic activity was investigated with unsubstituted TiO 2 , 1% Pd/TiO 2 (imp), and Ti 1-x Pd x O 2-δ (where x = 0.05-0.3). No appreciable NO conversion was observed over unsubstituted TiO 2 , although, despite competitive adsorption of NO and CO on the Pd 2+ sites, there was a significant reduction of NO over Ti 1-x Pd x O 2-δ . The kinetic model showed that the enhanced catalytic activity is due to the NO photodissociation at the oxide-ion vacancy.

Photocatalytic Decomposition of NO<sub>x</sub> Using Ti-, V-, and Mo-MCM-41 Catalysts

The photocatalytic reduction of NO into N 2 in the absence and presence of hydrocarbons were investigated on MCM-41 mesoporous molecular sieves including Ti, V, and Mo ions. Special attention was paid to the origin of the differences in their photocatalytic reactivities. Ti-MCM-41 showed much higher photocatalytic reactivity for the direct decomposition of NO into N 2 and O 2 than V- and Mo-MCM-41. However, the reactions on V- and Mo-MCM-41 were remarkably enhanced in the co-existence of propane. Such enhancement was not observed on Ti-MCM-41, showing a sharp difference. It was found that the charge transfer excited states of V- and Mo-oxide species exhibit a high reactivity for the hydrogen abstraction from propane, leading to a high efficiency in the photocatalytic reaction of NO and propane on V- and Mo-MCM-41. However, Ti-MCM-41 did not exhibit high reactivity for the hydrogen abstraction.

Synthesis, characterization and photocatalytic reactivities of Mo-MCM-41 mesoporous molecular sieves: Effect of the Mo content on the local structures of Mo-oxides

A series of Mo-MCM-41 mesoporous molecular sieves of varying Mo content were synthesized and the local structures of their active sites characterized by means of XRD, UV–vis, photoluminescence, and XAFS measurements. Mo-MCM-41 was found to possess three different types of Mo-oxide species, the concentrations of which were dependent on the Mo content: a highly dispersed tetra-coordinated monomeric molybdate, a tetra-coordinated dimeric and/or oligomeric molybdate, and a hexa-coordinated polymeric molybdate. Moreover, the tetra-coordinated molybdate species was observed to play a major role in the photocatalytic reduction of NO in the presence of CO to form N 2 and CO 2.

Electrochemical and gas-phase photocatalytic performance of nanostructured TiO2(B) prepared by novel synthetic route

Abstract Nanostructured phase pure TiO2(B) with microfibrous morphology was synthesized by newly developed protocol employing amorphous TiO2 as a precursor. Compared to traditional syntheses from K2Ti4O9, the new product exhibited better electrochemical performance and stability. Cyclic voltammetry of Li-insertion into the TiO2(B) evidences a pseudocapacitive faradaic process of Li accommodation which is basically different from the diffusion-controlled lithium storage in anatase or rutile. The presence of two pairs of peaks in cyclic voltammogram with formal potentials of ca. 1.5 and 1.6 V is specific for TiO2(B). This enables to use cyclic voltammetry for identification of this phase in a broad palette of TiO2 materials of various origin. The photocatalytic activity of TiO2(B) in a gas phase was evaluated using the total oxidation of propane with oxygen and the photocatalytic reduction of NO to N2 in an oxygen rich gas mixture. For the total oxidation of propane in the gas mixture containing 300 ppm propane and 20% oxygen, the reaction rates per 1 m2/g of the BET surface area of the catalyst for TiO2(B) prepared by our protocol and Hombifine N (anatase, SBET = 300 m2/g) are comparable. For the photocatalytic NO reduction to N2 in an atmosphere containing 20% oxygen the ratio of quantum yields for TiO2(B) and Hombifine N was found to be 0.08, which is roughly equivalent to the ratio of their BET surface areas (0.09), despite different phase composition of both materials. In comparison with the standard catalyst our material exhibited higher selectivity in the reduction of NO to N2.

Quantitative analysis of photoluminescence quenching of silica-supported molybdena catalysts. Relation to photocatalytic reduction of nitric oxide by carbon monoxide

The quenching effect of NO, O2, CO, and N2O on the photoluminescence of Mo6+/SiO2 has been studied at room temperature as a function of gas pressure. Nonlinear plots of the relative photoluminescence intensity I0/I (I0 is the initial intensity under vacuum) vs. pressure of the quenching gases were rationalized assuming that only adsorbed molecules efficiently quench the (Mo5+–O-)* excited state and that the fraction of adsorbed quenching molecules can be determined from the classical Langmuir-type adsorption isotherm. The ratio of the quenching rate constants for NO and CO calculated from the computer best fits of the experimental I0/I–pressure dependence is in agreement with earlier data on the kinetics of the photocatalytic reduction of NO by carbon monoxide on Mo6+/SiO2.

Degradation Characteristics of NO by Photocatalysis with TiO2 and CuO/TiO2

The effects of CuO loading, reaction temperature, and surface gas velocity (Ug) on the photocatalytic reduction of NO have been determined in an annular flow type and a modified two-dimensional fluidized bed photoreactor. The optimum CuO loading was found to be 3.3 wt.% and NO degradation conversion in the modified two-dimensional fluidized bed photoreactor is more than 70% at 2.5 Umf.