An XPS and STM study of the size effect in NO adsorption on gold nanoparticles

The effect of the gold particle size, temperature of the model gold catalyst, and NO pressure on the composition of the adsorption layer was studied by in situ XPS and STM methods. Adsorption of nitric oxide was carried out on gold nanoparticles with a mean size of 2?C7 nm prepared on the thin film surface of alumina. In high-vacuum conditions (P _NO ?? 10^?5 Pa), only atomically adsorbed nitrogen is formed on the surface of gold nanoparticles. At about 1 Pa pressure of NO and in the temperature range from 325 to 475 K, atomically adsorbed nitrogen coexists with the N₂O adsorption complex. The surface concentration of the adsorbed species changes with a change in both the mean gold particle size and adsorption temperature. The saturation coverage of the surface with the nitrogen-containing complexes is observed for the sample with a mean size of gold particles of 4 nm. The surface of these samples is mainly covered with atomically adsorbed nitrogen, the saturation coverage of adsorbed nitrogen of about ??0.6 monolayer is attained at T = 473 K. The change in the composition of the adsorption layer with temperature of the catalysts agrees with the literature data on the corresponding temperature dependence of the selectivity of N₂ formation observed in the catalytic reduction of NO with carbon monoxide on the Au/Al₂O₃ catalyst. The dependences of the composition of the adsorption layer on the mean size of Au nanoparticles (size effect) and temperature of the catalyst are explained by the sensitivity of NO adsorption to specific features of the gold surface.     

Dry Reforming of Methane on a Highly‐Active Ni‐CeO2 Catalyst: Effects of Metal‐Support Interactions on C−H Bond Breaking

Ni‐CeO₂ is a highly efficient, stable and non‐expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO₂ at temperatures as low as 300 K, generating CH_x and CO_x species on the surface of the catalyst. Strong metal–support interactions activate Ni for the dissociation of methane. The results of density‐functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO_2?x(111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CH_x or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way.     

Photoelectron spectra of the decomposition of ethylene on (110) tungsten

Photoelectron spectra, LEED patterns, and work function changes were obtained for ethylene adsorbed on (110) tungsten at room temperature, and with subsequent heat treatment. For saturated adsorption of C₂H₄ on (110) W at room temperature, features in the photoelectron spectrum were observed which are believed to be due to the C, HCC, and Cmetal bonds in an adsorbed species of the form C₂H₂. The work function decreased by 1.2 eV at saturation, but LEED showed no change from the clean surface pattern. Upon heating to ≈ 500 K, where hydrogen is known to desorb, the CH bond was broken, whereas the CC and Cmetal bonds remained. The work function increased, from saturation, by ≈ 0.6 eV and the LEED pattern exhibited a large diffuse background with no new spots. Upon heating to ≈ 1100 K the CC bond broke and the LEED pattern ordered into the characteristics carbon contamination pattern.     

Hydrogen production by aqueous phase reforming of sorbitol using bimetallic Ni–Pt catalysts: metal support interaction

Hydrogen was produced by Aqueous Phase Reforming (APR) of 10% (w/w) sorbitol using mono- and bi-metallic catalysts of Ni and Pt supported on alumina nano-fibre (Alnf), mesoporous ZrO₂ and mixed oxides of ceria–zirconia–silica (CZxS) with varying concentration of silica (where x is silica concentration). X-ray diffraction, TEM/EDS and temperature programmed reduction were also carried on these catalysts to study the surface properties. It was observed that co-impregnation of Pt and Ni in atomic ratio 1:12 increased the reducibility of Ni by forming an alloy. However, sequential impregnation of Ni followed by Pt does not form the bi-metallic particles to increase the Ni reducibility. Reduction peak of co-impregnated Ni–Pt/Alnf was found to be 270 °C lower than the sequentially impregnated Pt/Ni/Alnf. The presence of silica at high concentration in CZxS support decreased the reducibility of ceria by forming an amorphous layer on Ce_xZr_1?xO₂ crystals, which also decreased Ni reducibility. The rate of H₂ formation from aqueous phase sorbitol reforming was found to be highest for co-impregnated Ni–Pt catalysts followed by sequentially impregnated Pt/Ni and monometallic Ni catalyst. The H₂ activity decreased in the following order of the supports: Alnf > ZrO₂ > CZ3S > CZ7S.     

Methanol adsorption on γ-irradiated SiO2 surface

The adsorption of methanol on γ-irradiated and un-irradiated SiO₂ surfaces pretreated at 473 K was investigated by Fourier transform infrared spectroscopy, temperature programmed desorption (TPD) and pulse methods. Methanol adsorbed only in molecular form on the un-irradiated sample. Treating the pre-irradiated silica surface with methanol at room temperature formaldehyde and hydrogen were formed. The methanol adsorbed on the irradiated silica transformed to formyl groups during a longer time at room temperature and desorbed as formaldehyde simultaneously with CH₃OH (T_max=395 K) on the TPD.     

The influence of preadsorbed hydrogen and CO on adsorption of ethylene on the Pd(111) surface

The coadsorption of C₂H₄ with H₂ and CO on Pd(111) has been investigated at 300 and 330 K At 300 K two forms of adsorbed ethylene coexist on the surface in the presence of ethylene gas: a molecular form desorbing as C₂H₄ at 330 K and a dissociatively adsorbed form (giving only hydrogen in desorption spectra) which is stable both in vacuum and in hydrogen at 10^?8 Torr. The molecular form seems to be a precursor state for hydrogenation and for dissociative adsorption. Both processes are controlled by the amount of coadsorbed hydrogen which in turn is controlled by CO coverage.     

Effect of halides and alkali cations on the Zn(Hg)/Zn(II) electrode reactions

The title subject has been studied by galvanostatic single-pulse, chronopotentiometric and equilibrium measurements on the Zn(Hg)/Zn(II) electrode in x M KI+(1?x) M KCl (x from 0 to 1), 1 M KBr and 1 M MeCl (Me=Li, Na, K and Cs) solutions of pH 3 at 25°C. Quantitative information about the effect of specifically adsorbed halides on the rates of the Zn(II)/Zn(I) and the Zn(I)/Zn(Hg) steps is obtained separately (for the latter step mainly at potentials near ?1.0 V(SCE)), and the latter step seems to be more influenced than the former by the adsorption. An attempt is made to correlate the adsorption effect on the rate of the Zn(II)/Zn(I) step to double-layer parameters according to recent models for such effects. The extra current observed at potentials where the halides are adsorbed, seems to vary with the surface activity of the specifically adsorbed ion. The lack of any observed kinetic effect of Cs⁺, which is specifically adsorbed at these potentials, is possibly due to the Cs⁺ specific adsorption enhancing the Cl^? specific adsorption and vice versa, so that the decelerating and accelerating effects by these ions may cancel each other.     

NOx-Sorbing Metal Oxides, MnOx–CeO2. Oxidative NO Adsorption and NOx–H2 Reaction

(n)MnO_x–(1?n)CeO₂ binary oxides have been studied for the sorptive NO removal and subsequent reduction of NO_x sorbed to N₂ at low temperatures (≤150 °C). The solid solution with a fluorite-type structure was found to be effective for oxidative NO adsorption, which yielded nitrate (NO^? ₃) and/or nitrite (NO^? ₂) species on the surface depending on temperature, O₂ concentration in the gas feed, and composition of the binary oxide (n). A surface reaction model was derived on the basis of XPS, TPD, and DRIFTS analyses. Redox of Mn accompanied by simultaneous oxygen equilibration between the surface and the gas phase promoted the oxidative NO adsorption. The reactivity of the adsorbed NO_x toward H₂ was examined for MnO_x–CeO₂ impregnated with Pd, which is known as a nonselective catalyst toward NO–H₂ reaction in the presence of excess oxygen. The Pd/MnO_x–CeO₂ catalyst after saturated by the NO uptake could be regenerated by micropulse injections of H₂ at 150 °C. Evidence was presented to show that the role of Pd is to generate reactive hydrogen atoms, which spillover onto the MnO_x–CeO₂ surface and reduce nitrite/nitrate adsorbing thereon. Because of the lower reducibility of nitrate and the competitive H₂–O₂ combustion, H₂–NO reaction was suppressed to a certain extent in the presence of O₂. Nevertheless, Pd/MnO_x–CeO₂ attained 65% NO-conversion in a steady stream of 0.08% NO, 2% H₂, and 6% O₂ in He at as low as 150 °C, compared to ca. 30% conversion for Pd/γ–Al₂O₃ at the same temperature. The combination of NO_x-sorbing materials and H₂-activation catalysts is expected to pave the way to development of novel NO_x-sorbing catalysts for selective deNO_x at very low temperatures.     

Thermodynamical and structural insights of orange II adsorption by MgRAlNO3 layered double hydroxides

[Mg_1−x Al_x(OH)₂][(NO₃)_x, nH₂O] Layered Double Hydroxide (LDH) sorbents with variable Mg/Al molar (R=(1−x)/x) ratios were investigated for adsorption of azo dye, orange II (OII) at various pH and temperature conditions. Mg₂AlNO₃ displays the highest adsorption capacity with 3.611 mmol of OII per gram of Mg₂AlNO₃ at 40 °C. Adsorption isotherms have been fitted using the Langmuir model and free energy of adsorption (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were calculated. The experimental values for ΔG° in temperature range between 10 and 40 °C were found to be negative indicating that a spontaneous process occurred. Positive calculated enthalpy values, characteristic of an endothermic process were found. Characterization of solids (PXRD, FTIR, UV-vis, TGA/DTA, adsorption isotherm BET analysis, SEM and Zetametry) before and after adsorption showed that adsorption proceeds in two steps. First, adsorption occurs at the LDH surface, followed by intercalation via anion exchange.     

Investigation of Fe−Ni Mixed‐Oxide Catalysts for the Reduction of NO by CO: Physicochemical Properties and Catalytic Performance

A series of Fe?Ni mixed‐oxide catalysts were synthesized by using the sol–gel method for the reduction of NO by CO. These Fe?Ni mixed‐oxide catalysts exhibited tremendously enhanced catalytic performance compared to monometallic catalysts that were prepared by using the same method. The effects of Fe/Ni molar ratio and calcination temperature on the catalytic activity were examined and the physicochemical properties of the catalysts were characterized by using XRD, Raman spectroscopy, N₂‐adsorption/‐desorption isotherms, temperature‐programmed reduction with hydrogen (H₂‐TPR), temperature‐programmed desorption of nitric oxide (NO‐TPD), and X‐ray photoelectron spectroscopy (XPS). The results indicated that the reduction behavior, surface oxygen species, and surface chemical valence states of iron and nickel in the catalysts were the key factors in the NO elimination. Fe_0.5Ni_0.5O_x that was calcined at 250 °C exhibited excellent catalytic activity of 100 % NO conversion at 130 °C and a lifetime of more than 40 hours. A plausible mechanism for the reduction of NO by CO over the Fe?Ni mixed‐oxide catalysts is proposed, based on XPS and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses.     

The Adsorption and Thermal Decomposition of CH2CO (CD2CO) on Si(111)-7 × 7

The adsorption and thermal decomposition of ketene on Si(l 11)-7 × 7 were investigated using various surface analysis techniques. When the surface was exposed to ketene at 120 K, two CO stretching modes at 220 and 273 meV appeared in HREELS, corresponding to two adsorbed ketene states. After the sample was annealed at ?250 K, the 273 and the 80 meV peaks vanished, indicating the disappearance of one of the adsorption states by partial desorption of the adsorbate. In a corresponding TPD measurement, a desorption peak for ketene species was noted at 220 K. Annealing the sample at 450 K caused the decomposition of the adsorbate, producing CH_x and O adspecies. Further annealing of the surface at higher temperatures resulted in the breaking of the CH bond, the desorption of H and O species and the formation of Si carbide. The desorption of H at 800 K was confirmed by the appearance of the D₂ (m/e = 4) TPD peak at that temperature when CD₂CO was used instead of CH₂CO.     

The mechanism of methanol formation and other reactions following formaldehyde adsorption on Ni(110)

The adsorption/desorption and reactive behavior of formaldehyde was studied on clean single-crystal Ni(110) at adsorption temperatures down to 200 °K. For low exposures of the surface to formaldehyde, hydrogen and CO binding states were populated due to decomposition of the molecule upon adsorption. Higher exposures gave rise to a decomposition-limited hydrogen peak exhibiting an activation energy of 20 kcal/gmol and an apparent frequency factor of 10¹⁴ sec^?1. At initial coverages of H₂CO exceeding about 0.5, monolayer methanol was observed to form. The formation of methanol involved a hydrogen atom transfer between two adsorbed H₂CO molecules and did not occur totally via surface hydrogen. Self-oxidation to form CO₂ was also observed. The surface exhibited reaction heterogeneity, and the surface reactivity was observed to depend on the temperature of adsorption of reactants, suggesting strong adsorbate-induced surface “reconstruction.”     

Behavior of adsorbed diphenyl-sulfide on the Pd/C catalyst for o-chloronitrobenzene hydrogenation

A series of diphenyl-sulfide（Ph₂S）-immobilized Pd/C catalysts(Pd-Ph₂S_（X）/C) were prepared using the wetness-impregnation and immobilization method.Pd-Ph₂S_（x）w/C catalysts employed for the hydrogenation of o-chloronitrobenzene showed very high selectivity.The structure of Pd-Ph₂S_（x）/C with different molar ratio of ligand（x-values） was characterized by XPS and TG-DSC-MS.The results suggest a "saturated" surface ratio of Ph₂S/Pd（about 0.3） was formed on the Pd-Ph₂S_（x）/C catalysts surface.The Ph₂S immobilized on the Pd particle is quite stable,and the desorption of Ph₂S or dissociative loss of phenyl group was only found at temperatures above 500 K.The possible catalytic mechanism of the Pd-Ph₂S_（x）/C catalyst was also discussed.     

The impact of surface Cu2+ of ZnO/(Cu1−xZnx)O heterostructured nanowires on the adsorption and chemical transformation of carbonyl compounds

The surface cation composition of nanoscale metal oxides critically determines the properties of various functional chemical processes including inhomogeneous catalysts and molecular sensors. Here we employ a gradual modulation of cation composition on a ZnO/(Cu_1−xZn_x)O heterostructured nanowire surface to study the effect of surface cation composition (Cu/Zn) on the adsorption and chemical transformation behaviors of volatile carbonyl compounds (nonanal: biomarker). Controlling cation diffusion at the ZnO(core)/CuO(shell) nanowire interface allows us to continuously manipulate the surface Cu/Zn ratio of ZnO/(Cu_1−xZn_x)O heterostructured nanowires, while keeping the nanowire morphology. We found that surface exposed copper significantly suppresses the adsorption of nonanal, which is not consistent with our initial expectation since the Lewis acidity of Cu²⁺ is strong enough and comparable to that of Zn²⁺. In addition, an increase of the Cu/Zn ratio on the nanowire surface suppresses the aldol condensation reaction of nonanal. Surface spectroscopic analysis and theoretical simulations reveal that the nonanal molecules adsorbed at surface Cu²⁺ sites are not activated, and a coordination-saturated in-plane square geometry of surface Cu²⁺ is responsible for the observed weak molecular adsorption behaviors. This inactive surface Cu²⁺ well explains the mechanism of suppressed surface aldol condensation reactions by preventing the neighboring of activated nonanal molecules. We apply this tailored cation composition surface for electrical molecular sensing of nonanal and successfully demonstrate the improvements of durability and recovery time as a consequence of controlled surface molecular behaviors.

Unexpected features of surface Cu²⁺ on ZnO/(Cu1−xZnx)O nanowires for molecular transformation and electrical sensing of carbonyl compounds were found.     

Low temperature adsorption of CO on plycrystalline molybdenum,studied by X-ray and vacuum UV photoelectron spectroscopy

The adsorption of CO on a polycrystalline Mo film at ～80°K has been studied by X-ray and UV photoelectron spectroscopy (XPS and UPS). Two adsorption states were revealed by XPS, the ratio of the O(1s) intensities from these two states was about 4 : 1 at saturation coverage (P_CO ～ 10^?6 torr). Broad resonances corresponding to the MO's of CO(ads) are observed in the UPS spectrum. On warming to room temperature chemical shifts of about 1.2 and 1.9 eV to lower binding energies were observed for the O(1s) and C(1s) signals of the major CO(ads) component. The minor state desorbed as anticipated from previous adsorption studies. The XPS spectrum observed at room temperature was virtually identical to that previously reported for CO adsorbed at room temperature. On warming the ‘orbital’ of adsorbed CO revealed by UPS is replaced by a structure apparently characteristic of carbon and oxygen atoms. These results suggest that low temperature adsorption takes place predominantly into a molecular state which on warming to room temperature dissociates.     

不同氮掺杂量碳纳米管的合成和表征

以不同氮含量的有机胺为碳和氮源，用催化方法合成出了不同氮含量的大管径碳纳米管。采用Fe/SBA-15分子筛为催化剂，有机胺经过1 073 K高温裂解得到氮掺杂碳纳米管材料(CN_x)。比较了苯、三乙胺、二乙胺、乙二胺四种原料对合成CN_x形貌、产率、掺氮量和吸水率的影响；以二乙胺为原料合成出适中的氮碳比(N/C原子比为0.15)和较高产率(2.2 g·（g·cat）^-1)的竹节状CN_x材料。     

Grafted block complex coacervate core micelles and their effect on protein adsorption on silica and polystyrene

We have studied the formation and the stability of grafted block complex coacervate core micelles (C3Ms) in solution and the influence of grafted block C3M coatings on the adsorption of the proteins β-lactoglobulin, bovine serum albumin, and lysozyme. The C3Ms consist of a grafted block copolymer PAA₂₁-b-PAPEO₁₄ (poly(acrylic acid)-b-poly(acrylate methoxy poly(ethylene oxide)), with a negatively charged PAA block and a neutral PAPEO block and a positively charged homopolymer P2MVPI (poly(N-methyl 2-vinyl pyridinium iodide). In solution, these C3Ms partly disintegrate at salt concentrations between 50 and 100 mM NaCl. Adsorption of C3Ms and proteins has been studied with fixed-angle optical reflectometry, at salt concentrations ranging from 1 to 100 mM NaCl. In comparison with the adsorption of PAA₂₁-b-PAPEO₁₄ alone adsorption of C3Ms significantly increases the amount of PAA₂₁-b-PAPEO₁₄ on the surface. This results in a higher surface density of PEO chains. The stability of the C3M coatings and their influence on protein adsorption are determined by the composition and the stability of the C3Ms in solution. A C3M-PAPEO₁₄/P2MVPI₄₃ coating strongly suppresses the adsorption of all proteins on silica and polystyrene. The reduction of protein adsorption is the highest at 100 mM NaCl (>90%). The adsorbed C3M-PAPEO₁₄/P2MVPI₄₃ layer is partly removed from the surface upon exposure to an excess of β-lactoglobulin solution, due to formation of soluble aggregates consisting of β-lactoglobulin and P2MVPI₄₃. In contrast, C3M-PAPEO₁₄/P2MVPI₂₂₈ which has a fivefold longer cationic block enhances adsorption of the negatively charged proteins on both surfaces at salt concentrations above 1 mM NaCl. A single PAA₂₁-b-PAPEO₁₄ layer causes only a moderate reduction of protein adsorption.     

Scanning tunneling microscopic investigations of the adsorption and segregation of carbon and sulfur on nickel single crystal surfaces

The adsorption and segregation of carbon or sulfur on Ni single crystal surfaces have been investigated by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Different adsorbate(segregate)-induced surface modifications have been detected in dependence on the original Ni surface orientation and the kind of nonmetal atoms: i) Adsorption of carbon from ethylene on Ni(111) at 6.7×10^–4 Pa and 1000K leads to the epitaxial growth of a graphitic carbon monolayer which exhibits the structure of the hexagonal basal plane of graphite. However, as is found for highly oriented pyrolytic graphite (HOPG), only three of six carbon atoms of the (0001) graphite plane are imaged by STM. In contrast, on Ni(771) at 663 to 1000 K carbon islands have been formed but no graphite monolayer formation is detected. This behavior can be understood by considering the aspects that no large-area epitaxy between the graphite basal plane and the Ni(110) terraces exists and that the surface carbon activity was too low to initiate substrate restructuring. ii) Segregation of sulfur (from the Ni bulk containing 5 to 7 ppm S) on Ni(110) at 1043K and _s0.4 ML initiates the growth of sulfur islands which show a c(2×2)-S overlayer structure, whereas on Ni(111) at 823K and _s0.2 ML (average value) a reconstructed surface phase is forming which can be described as an adsorbed two-dimensional sulfide Ni₂S.     

高硅 Na-ZSM-5 分子筛表面 NO 的常温吸附-氧化机理

 采用程序升温表面反应 (TPSR) 和原位漫反射红外光谱 (DRIFTS) 等手段研究了常温下 NO 和 O₂ 在高硅 Na-ZSM-5 分子筛上吸附-氧化反应机理. 结果表明, Na-ZSM-5 分子筛上 NO 的催化氧化过程中伴随着显著的 NO₂ 物理吸附, 表现为 NO 氧化和 NO₂ 吸附间的动态平衡. Na-ZSM-5 分子筛表面 NO_x 吸附物种的 TPSR 和原位 DRIFTS 表征表明, 化学吸附的 NO 和气相中的 O₂  在 Na-ZSM-5 表面反应生成吸附态的 NO₃, 并继续与 NO 作用生成弱吸附的 NO₂  和 N₂ O₄, 它们吸附饱和后释放出来; 其中, 强吸附的 NO₃ 在 NO 氧化过程中起到了反应中间体的作用, 同时也促进了 NO 的吸附.