Desorption Intensity Research Articles

Doping-Dependent Adsorption and Photon-Stimulated Desorption of CO on GaN(0001)

CO is used as a chemical probe molecule to elucidate the properties of differently n-type doped GaN(0001) surfaces under ultrahigh vacuum conditions. Doping-dependent sticking of CO is observed by temperature-programmed desorption, which is not influenced by the surface composition of the semiconductor substrates. By the excitation of the semiconductor with UV photons a low-temperature desorption of CO is stimulated. The absolute photon-stimulated desorption intensity strongly depends on the surface composition. However, the desorption kinetics do not significantly depend on the surface composition, semiconductor doping, or UV excitation wavelength. A model is introduced, which is based on the electronic characteristics of the GaN substrates and describes the doping-dependent adsorption as well as the photochemical behavior.

Kinetics and Adsorption-Desorption Behavior of AM Nitrification Inhibitor in Mollisols

ABSTRACTKinetics and adsorption-desorption behavior of a potent nitrification inhibitor, 2-amino 4-chloro 6-methyl pyrimidine (AM), was examined in Mollisol samples of different depths. Adsorption of AM was better accounted by pseudo-second order kinetics. Adsorption and desorption data of AM onto soil samples of different depths conformed to single surface Freundlich isotherm model. The values of ln K varied from −0.1515 (0–15 cm) to 1.5171 (45–60 cm) and of 1/n from 0.9961 (45–60 cm) to 1.3237 (30–45 cm). Computed values of desorption capacity (ln K’) varied from 3.4734 (0–15 cm) to 4.0674 (45–60 cm) while that of 1/n´ from 0.0017 (45–60 cm) to 0.0367 (0–15 cm). Intensity of desorption (1/n´) had significant positive correlation with soil electrical conductance and clay content. The values of desorption index (n´/n) varied from 14.60 (0–15 cm) to 472.33 (30–45 cm) indicating high degree of irreversibility of adsorbed AM and hence poor leaching from these soils.

Fast evaluation of the coalbed methane content of coal viewed as an element leading to improvement in exploitation conditions

Abstract Methane, as a co-occurring compound, can be found in the majority of coal basins all over the world. The knowledge of methane content is a basic piece of information used in balancing and describing a given coal seam, in conducting safe exploitation – with methane hazards and methane and rock outburst hazards in mind – as well as in less common procedures, such as coal seam fracturing and methane extraction, or storing carbon dioxide in off-balance coal seams. The author of the present paper outlines a thoroughly modified desorbometric method used to analyze the coal-methane system. The research object, in underground conditions, is the full process of releasing methane from coal, which makes it possible to determine gas losses, the desorbable methane content, and the effective diffusion coefficient. This type of research can be conducted in less than 24 hours due to the reduction of the grain fraction of the analyzed bore dust. The thorough research in underground conditions was preceded by a model analysis of the simultaneous impact of the desorbable methane content in coal and the effective diffusion coefficient upon the value of the desorption indensity index. The influence of a grain fraction on the kinetics of methane release from coal was described, and the 0.20–0.25 [mm] grain fraction was selected. The choice of this particular fraction made it possible to register the full process of methane release from coal, in the assumed time. An original methodology of performing underground measurements was presented, together with an instrument used to perform these measurements. The underground research involved measuring the desorbable methane content according to the presented original methodology, which was done simultaneously with an analysis of the coalbed methane content carried out by means of the bore dust method, an analysis of desorption intensity, and an analysis of the technical parameters of coal. The results point to a substantial discrepancy between the desorbable methane content in coal and the coalbed methane content measured by the bore hole method in compliance with the Polish standard. The mean relative percentage error for 17 measurements was 6.5%. The author provided an example concerning using the effective diffusion coefficient in explaining substantial differences in the desorption intensity index for two samples characterized by the similar coalbed methane content.

New Instruments and Methods for Analysing the Coal-Methane System

Abstract The authors of the present paper designed and constructed a prototype of an instrument which enables fully automated determination of the desorbable methane content and effective diffusion coefficient in underground conditions. Due to microprocessor analysis of the recorded data and the application of the mathematical model of the diffusion process, it is possible to automatically determine the amount of methane whose release from a coal sample occurred before the sample was placed within a measuring instrument. It is also possible to carry out follow-up extrapolation of the recorded data so the time duration needed to determine reliable results can be reduced. The instrument was tested and optimized, and a number of copies sufficient for performing underground tests were constructed. The concept of the instrument represents a totally new approach to the observation of gas release from a coal sample. Instead of short-period measurements, virtually the whole process of methane release from coal is registered and analysed. This is possibly due to the use of a grain fraction lower than one mm which is presently applied for the sake of evaluating the methane- bearing capacity and desorption intensity.

Mechanical and gaseous properties of coal briquettes in terms of outburst risk

Scientific research often require application of samples with repeatable properties. This demand is difficult to fulfill especially in case of experiments concerning coals. Therefore, a necessity occurs to use a material which stands for coal and is characterized with properties similar to coal. Authors of this article suggest, in required situations, the use of coal briquette as a research material. Huge advantage of coal briquettes application is the fact that in many aspects their properties are similar to the structurally deformed coal (altered coal) which presence, according to recent research, is closely related to areas of increased outburst risk. Authors have conducted studies of mechanical and gaseous properties of coal briquettes. The experimental part of the presented studies included the preparation of coal briquettes of a various porosity (from 13.5% to 33%) and determination of their mechanical parameters: uniaxial compressive strength and Protodiakonov coefficient as well as determination of their gaseous parameters: desorption intensity and adsorption capacity. The properties of coal briquettes were analyzed and referenced to the properties of normal coal and altered coal, characterized by mechanical and gaseous properties specific for coals that are hazardous and prone to outbursts. Dependences between the determined uniaxial compressive strength Rc and porosity, Protodiakonov coefficient f and porosity as well as the relationship between Rc and f for the studied coal briquettes were expressed mathematically. Threshold value of f (equal to 0.3), introduced for Polish outburst prevention, corresponded to 18.5% porosity of coal briquette. Changeover of coal briquette’s porosity provides aprospect of obtaining a coal material which have Rc and f parameters typical for coals occurring in natural conditions. Coal briquette of experimentally determined porosity may replicate the mechanical properties of normal or altered coal. Adsorption capacity of different coal samples (briquette, normal, altered) depended on the coal microstructure and the grinding level of coal. The relationship between the 2min desorption intensity and the methane saturation pressure for different coal samples (briquette, normal, altered) showed that if the grains constituting the grain fraction were larger the amounts of methane desorbed (for the studied time interval) were smaller. A correlation between coal briquette’s porosity and amount of methane released during 2min desorption test was not found. Grinding level of coal material creates a new distribution of grain size and it determines diffusion and seepage rate of gas releasing from the inside area of the pores. It was shown in this work that mechanical and gaseous properties of coal briquettes predispose them to conduct representative outburst research. A proper method of coal material preparation for the briquetting process is a key point for future properties of coal briquettes.

Investigations on Methane Emission from Flooded Workings of Closed Coal Mines

The migration of methane towards the surface, within mining areas of closed mines, can be a danger to public safety for many of years after the process of liquidation has been finished. The liberation of methane from undisturbed coal seams, and those destressed through earlier mining has not been fully recognised so far. Knowledge of the effect of the presence of water, along with hydrostatic pressure, on the intensity of methane desorption from destressed seams is necessary in determining the approximate volume of methane inflowing, within a period of time, into a closed mine. Laboratory tests on these relationships have been carried out in accordance with proper research methodology by the National Institute for the Environment and Industrial Hazards (INERIS), France with the Central Mining Institute, Katowice, Poland. The results have facilitated determining the effect of hydrostatic pressure variation of water on the intensity of methane desorption from flooded coal. These results has been practically applied in predicting the emission of methane into closed mines, and in orienting the rules of methane hazard control, both during the process of mine closure, and on the surface of post-mining areas.

Growth, solvent effects, and thermal desorption behavior of octylthiocyanate self-assembled monolayers on Au(111)

The growth process, solvent effects, and thermal desorption behavior of octylthiocyanate [OTC, CH(3)(CH(2))(7)S-CN] self-assembled monolayers (SAMs) on Au(111) were characterized by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). To investigate their growth processes, octanethiol [OT, CH(3)(CH(2))(7)S-H] and OTC SAMs were prepared in 0.5 μM ethanol solution at room temperature as a function of immersion time: 10 min, 1 h, 2 h, and 24 h. STM imaging revealed that OT SAMs underwent a phase transition from the liquid phase containing striped-phase domains to the closely packed c(4 × 2) phase. OTC SAMs underwent a different phase transition from the liquid phase containing aggregated molecules to the disordered phase containing striped-phase domains. The adsorption amounts of OTC SAMs formed after immersion for 10 min and 24 h were measured to be 16% and 30% smaller than those of OT SAMs under the same conditions. STM and XPS results show that the growth kinetics of OTC SAMs on Au(111) are much slower than those of OT SAMs. Hexane resulted in OTC SAMs of higher structural quality than ethanol, DMF, or toluene. TDS measurements revealed that the relative desorption intensities of octanethiolate (C8S(+), monomer) and dioctyl disulfide (C8SSC8(+), dimer) to octanethiol (C8SH(+)) fragments for OTC SAMs were much weaker than those of OT SAMs. This is because desorption of monomers and dimers is strongly suppressed by low surface coverage of OTC SAMs, as revealed by STM observations.

Photocatalytic oxidation of indoor toluene: Process risk analysis and influence of relative humidity, photocatalysts, and VUV irradiation

Concentrations of 13 gaseous intermediates in photocatalytic oxidation (PCO) of toluene in indoor air were determined in real-time by proton transfer reaction mass spectrometry and desorption intensities of 7 adsorbed intermediates on the surface of photocatalysts were detected by temperature‐programmed desorption‐mass spectrometry. Effects of relative humidity (RH), photocatalysts, and vacuum ultraviolet (VUV) irradiation on the distribution and category of the intermediates and health risk influence index (η) were investigated. RH enhances the formation rate of hydroxide radicals, leading to more intermediates with higher oxidation states in gas phase. N doping promotes the separation of photo-generated electrons and holes and enhances PCO activity accordingly. VUV irradiation results in higher mineralization rate and more intermediates with higher oxidation states and lower toxicity e.g. carboxylic acids. Health risk analysis indicates that higher RH, N doping of TiO2, and VUV lead to “greener” intermediates and smaller η. Finally, a conceptual diagram was proposed to exhibit the scenario of η varied with extent of mineralization for various toxicities of inlet pollutants.

Influence of Surface Morphology and Substrate on Thermal Stability and Desorption Behavior of Octanethiol Self-Assembled Monolayers: Cu, Ag, and Au

The formation and thermal desorption behaviors of octanethiol (OT) SAMs on single crystalline Au(111) and polycrystalline Au, Ag, and Cu substrates were examined by X-ray photoelectron microscopy (XPS), thermal desorption spectroscopy (TDS), and contact angle (CA) measurements. XPS and CA measurements revealed that the adsorption of OT molecules on these metals led to the formation of chemisorbed self-assembled monolayers (SAMs). Three main desorption fragments for dioctyl disulfide (C8SSC8+, dimer), octanethiolate (C8S+), and octanethiol (C8SH+) were monitored using TDS to understand the effects of surface morphology and the nature of metal substrates on the thermal desorption behavior of alkanethiols. TDS measurements showed that a sharp dimer peak with a very strong intensity on single crystalline Au(111) surface was dominantly observed at 370 K, whereas a broad peak on the polycrystalline Au surface was observed at 405 K. On the other hand, desorption behaviors of octanethiolates and octanethiols were quite similar. We concluded that substrate morphology strongly affects the dimerization process of alkanethiolates on Au surfaces. We also found that desorption intensity of the dimer is in the order of Au ≫ Ag > Cu, suggesting that the dimerization process occurs efficiently when the sulfur–metal bond has a more covalent character (Au) rather than an ionic character (Ag and Cu). The relative desorption intensity of the octanethiolates to the octanethiols follows the order of bond strength, Cu > Au > Ag. Alkanethiolates may be a dominant desorption product as metal–sulfur bonds become stronger. In this study, we clearly demonstrate that the thermal stability and desorption behaviors of alkanethiol SAMs are strongly influenced by the surface morphologies of metal substrates, bonding character of the sulfurs, the bond strength of metal–sulfur, and van der Waals interactions. Our results provide new insights into understanding the thermal stability and desorption behaviors of alkanethiols on Au, Ag, and Cu surfaces.

Nonisothermal desorption of droplets of complex compositions

This paper presents the process of nonstationary evaporation of aqueous solutions of LiBr-H2O, CaCl2-H2O, NaCl-H2O droplets on a horizontal heating surface. The following typical stages of heat and mass transfer depending on wall temperature have been considered: evaporation below boiling temperature and nucleate boiling. The significant decrease in desorption intensity with a rise of initial mass concentration of salt has been observed. Formation of a surface crystallization front at evaporation of a droplet has been detected. We have developed the experimental method for direct measurements of the mass of evaporating droplet.

Hydrogen released from bulk ZnO single crystals investigated by time-of-flight electron-stimulated desorption

Electron beam (e-beam) irradiation effects on ZnO single crystals have been investigated by using time-of-flight electron-stimulated desorption (TOF-ESD). The samples were irradiated by using a continuous 0.5 or 1.5 keV e-beam, while the TOF-ESD spectra were taken by using a pulsed 0.5 keV e-beam. For both the O-terminated and Zn-terminated surfaces, the major desorption is H+ desorption. The main trend of H+ desorption intensity and evolution as a function of irradiation time is similar for both faces. The H+ peak is much higher after 1.5 keV irradiation than after 0.5 keV irradiation. The intensity of the H+ peak decreases exponentially as a function of irradiation time and partially recovers after the irradiation is stopped. These observations suggest that the main contribution of the H+ desorption is hydrogen released from the dissociation of H-related defects and complexes in the bulk region of the ZnO by e-beam irradiation. This finding can be used to explain the reported ultraviolet degradation of ZnO single crystals under electron irradiation observed by cathodoluminescence. The surfaces play a lesser role for the H+ desorption, as there are differences of the decreasing rate between the two faces and additionally the intensity of the H+ peak for both the unclean O-face and Zn-facesis smaller than that for clean faces. While the H+ desorption is mainly dominated by the bulk region, O+ desorption is more influenced by the surfaces. There are two kinds of O+ desorbed from ZnO having 13.0 μs TOF and 14.2 μs TOF. The O+ desorption depends on the surface polarity, the surface conditions and the energy used for irradiation.

Light-induced atom desorption for cesium loading of a magneto-optical trap: Analysis and experimental investigations

With the help of light-emitting diodes at the center wavelength of 470 nm, we demonstrate that light-induced atom desorption (LIAD) can be used for flexibly controlling the loading of magneto-optical traps (MOT) of cesium atoms. Under an ultralow background pressure in a quartz cell without any wall coating, we show that low intensity blue light can be used to control the loading rates (from 200 to 4000 atoms/s) and the number of cesium atoms (on the order of ${10}^{4}$ in our experiment) in a MOT without the use of dispensers or any secondary atom source. A theoretical model based on an atom loading rate equation is built which can simulate the magneto-optical trap loading process with LIAD. The theoretical results are in agreement with experimental data. Some important parameters of the vacuum system are determined accordingly. The decay time of the vacuum pressure is about 70 ms, which is much shorter than the usual vacuum system for experiments on atomic ensembles. It is very difficult to measure such short times by the traditional fluorescence detection of cold atoms due to the slow loading process. The change of desorption rate (on the order of ${10}^{13}\text{ }\text{atoms}/\text{s}$) for the different desorption intensities is also determined based on the background pressure caused by noncesium atoms in the cell. According to the experimental data and theoretical calculations, we obtain a partial pressure of about $1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\text{ }\text{Torr}$ for the untrapped cesium atoms and about $6.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\text{ }\text{Torr}$ for the noncesium atoms at the moment the desorption light is turned off. The system is almost an ideal vacuum system for transferring atoms into another region for further experiments.

Quantitation of Trace Metals in Liquid Samples by Dried-Droplet Laser Ablation Inductively Coupled Plasma Mass Spectrometry

A new, discrete sample introduction approach based on laser ablation (LA) is described for the quantitation of several trace metals in aqueous samples by ICPMS. Dried microdroplets of sample, previously mixed with a sodium acetate matrix, were quantitatively ablated from a polystyrene substrate. Calibration via the method of standard additions or isotope dilution provided accurate results for Ni, Cd, and Pb in drinking water and Se in a yeast extract. Compared to conventional solution nebulization, LA sample introduction provided a 2-7-fold enhancement in absolute sensitivity and transport efficiency of 2-14% for the elements examined. Estimated detection limits are 1-7-fold poorer for the dried-droplet LA technique, primarily a result of degraded precision arising from counting statistics limitations for discrete sample introduction. On the basis of the several-second half-width of the resulting transient signals, sample throughput can be in the range of 250 samples per hour. Additionally, integration of the transient signal should eliminate contributions to elemental fractionation from the LA step. Dried-droplet LA-ICPMS offers several advantages over its counterpart, ETV-ICPMS, with respect to background intensity, throughput, and ease of desorption.

Effects of the oxygen vacancy on NO adsorption at the TiO2 surface

The desorption spectrum of NO adsorbed on the surface of TiO2 powder was determined by temperature programmed desorption. The molecular orbital theory was u tilized to investigate the crystal cluster model of NO adsorbed on TiO2 and th e change of band gap in the adsorption process. The results indicate that there exist two peak temperatures, 450 and 980K, as N2 desorption followed by the NO adsorption on TiO2 The intensity of N2 desorption decre ases if the TiO2 powder is pretreated in an O2 atmosphere. The nitrogen atoms of the adsorbed NO gas recombine into N2 for desorption while oxygen atoms occupy th e oxygen vacancies in the TiO2 surface. The calculation analysis from the mole cular orb ital theory supports the deduction that the existence of oxygen vacancy on TiO2(110) surface offers a suitable condition of crystal surface for NO ad sorption.

Intrinsic and extrinsic factors in anion electron-stimulated desorption: D− from deuterated hydrocarbons condensed on Kr and water ice films

The results of D(-) ion desorption induced by 3-20 eV electrons incident on condensed CD(4), C(2)D(6), C(3)D(8), C(2)D(4), and C(2)D(2) are presented. These compounds were deposited in submonolayer amounts on the surfaces of multilayer solid films of Kr and nonporous and porous amorphous ice. While desorption of the D(-) anions proceeds via well-known processes, i.e., dissociative electron attachment (DEA) and dipolar dissociation, significant perturbations of these processes due to presence of the different film substrates are observed. We have shown that it is possible to distinguish between the character and nature of these perturbations. The presence of the nonporous ice perturbs the D(-) desorption intensity by affecting the intrinsic properties of the intermediate anion states through which dissociation proceeds. On the other hand, the presence of the porous ice introduces extrinsic effects, which can affect electron energy losses prior to their interaction with the hydrocarbon molecule and/or the energies and intensities of the fragment species after dissociation. Simple mechanisms responsible for the observed variations in the intensities of desorbed anionic signals are proposed and discussed. Electron transfer from transient anion states to electron states of the substrate film or nearby hydrocarbon molecules appear as the most efficient mechanism to reduce the magnitude of the DEA process.

Thermal desorption of carbon monoxide from Mo(110)

Adsorption and desorption of carbon monoxide (CO) from Mo(110) have been investigated by temperature programmed desorption (TPD). The TPD spectra exhibit peaks in two temperature regions: 250-400 and 850-1100 K. The first region correspond to adsorption in molecular form, whereas the latter region corresponds to desorption of CO that has been dissociatively adsorbed. When the surface was saturated by CO, about 35% of the desorption intensity originates from the high-temperature region (recombinative desorption) and the remaining desorption signal is from the low-temperature region (molecular adsorption). Desorption parameters for molecular adsorbed CO were obtained using several different heating rates. Desorption energies were estimated to range from 0.9 eV for low coverages of CO to about 0.65 eV for high coverages. Corresponding prefactors were estimated to be in the range from 1 21011 to 1 2109 sm 1. The experimental data have been compared with Monte Carlo simulations of first-order TPD from a bcc (110) lattice, in which partial poisoning of adsorption sites by dissociated carbon and oxygen was modelled. Repulsive near-neighbour interactions were used.

Electron stimulated desorption from molecules on a noble gas solid: an analysis of cluster and island formation upon deposition

Desorption of negative fragment ions following low energy electron impact to a two monolayer (ML) adsorbate of CHF 2Cl is studied. Results are compared for a deposition of the 2 ML quantity directly on a monocrystaline gold substrate with that on the surface of a Xe film as a spacer to the metal. The desorption intensity (Cl −, F −) is strongly suppressed when going from the metal to the rare gas film. For a uniformly covered surface one would expect the opposite behaviour, namely an enhanced desorption from molecules on the rare gas spacer. We interpret this observation by cluster and island formation on the rare gas film after CHF 2Cl deposition. A general analysis of cluster and island format for the fluorchloromethanes on a rare gas surface is performed.

Grouping soils of the Montreal Lowlands (Quebec) according to fertility and P sorption and desorption characteristics

Soil tests P (STP) developed to estimate P fertilizer needs and designed to produce optimal economic crop yields, are often not well suited to assess potential environmental impact of fertilization practices. The objective of this study was to develop interpretative soil groupings of the Montreal Lowlands area (MLA) based on soil physico-chemical properties and on soil P sorption and desorption characteristics. Soil P sorption and desorption characteristics together with STP may help in evaluating potential risks of soil P addition. Sixty-six soil types (phases of soil series based on surface texture) were selected as representative soils of the study area. Twenty-seven soil properties were used, including Mehlich-3 extractable P and Al, ammonium-oxalate extractable P, Fe and Al, P sorption index (Psi) and Bray-2 extractable P(BR2P). Multivariate analysis was applied to generate clusters and interpret soil groupings. Principal components analysis yielded two components related: (1) to soil inherent fertility (texture) and (2) to P sorption capacity and desorption intensity. The Ward's clustering method was then applied to the first two component scores. Five soil fertility groups were obtained. Multiple discriminant analysis proposed a classification model using a small subset of variables. Five variables were selected among the soil survey characteristics for discriminating soil groups: clay content, pH measurement in water, cation exchange capacity, BR2P and ammonium-acetate extractable Mg. Adding Psi in the model improved the classification correctness. The results of this study indicate that physico-chemical properties of the surface layer used together with soil P sorption-desorption characteristics contributed to the development of an interpretative grouping that may also be useful to assess vulnerability to water contamination by P. Key words: Soil behavior, soil fertility groups, multivariate analysis techniques

Femtosecond near-infrared laser desorption of multilayer benzene on Pt{111}: spatial origin of hyperthermal desorption

The intense (10 12 W cm −2, 800 nm) near-infrared laser desorption of benzene adsorbed on Pt{111} is reported. Velocity distributions are measured up to an adsorbate coverage of 20 monolayers. The velocity distributions reveal up to three distinct features: a hyperthermal feature with translational energy of 0.2 eV, a thermal feature and a subthermal feature. The translational energy of the hyperthermal feature is relatively independent of coverage and maintains constant desorption intensity from 4 to 20 ML. Experiments employing layered films of C 6H 6 and C 6D 6 reveal that the hyperthermal feature originates in the layers closest to the multilayer–vacuum interface.

Temperature-programmed desorption study of NO and CO 2 over CeO 2 and ZrO 2

The adsorptive properties of CeO 2 and ZrO 2 were studied with respect to NO and CO 2 probe molecules using temperature-programmed desorption (TPD). Four species were detected during thermal desorption of NO adsorbed on CeO 2 and ZrO 2, namely, NO ( m/ e = 30), N 2 ( m/ e = 28), N 2 O ( m/ e = 44) and O 2 ( m/ e = 32). The TPD profile suggest that there are two types of adsorbed states of NO on the CeO 2 and ZrO 2 surfaces, one is the weakly adsorbed NO which desorbs at about 170°C and the other is the more strongly adsorbed NO which desorbs at about 450°C. The adsorbed NO undergoes extensive decomposition to form N 2, N 2O and O 2 during thermal desorption. The TPD spectrum obtained after CO 2 adsorption on CeO 2 are composed of CO 2 desorption at 140°C and 440°C. These peaks are assigned to monodentate and bidentate carbonate species in the adsorbed states. After the successive adsorption of NO and CO 2 on the CeO 2 and ZrO 2 surfaces, the intensity of CO 2 desorption peak in TPD is weaker than that in the case of single of CO 2. However, the intensity of NO desorption is almost the same as in the case of single NO adsorption. This indicated that the preadsorption of NO on cation sites of oxide surfaces affected the surrounding surface oxygen sites and blocked the CO 2 adsorption. Furthermore, this also indicates that the interaction of the oxide surface with NO is much stronger than that with CO 2.