Stable Compositions and Structures of Copper Oxide Cluster Cations Cu n O m + (n = 2-8) Studied by Ion Mobility Mass Spectrometry

Stable compositions and structures of copper oxide cluster cations have been studied by ion mobility mass spectrometry (IMMS) and density functional theory calculations. Cluster ions of the series Cu n O m + were predominantly observed with n:m ≈ 2:1 in the mass spectrum. Collision cross sections (CCSs) of the cluster ions with n:m ≈ 2:1, determined by IMMS, were found to increase monotonically with cluster size. In addition, the CCSs of Cu n O n + and Cu n O n-1 + (n = 2-8) were examined, and stepwise increases were observed for Cu n O n-1 + series. These cluster structures were assigned by comparison of the CCSs obtained via the IMMS experiment with theoretical orientation-averaged CCSs of optimized structures.

On the Chemistry of Iron Oxide Supported on γ-Alumina and Silica Catalysts

Catalysts of iron oxide on γ-alumina and silica which were prepared by an incipient wetness impregnation technique have been investigated in an effort to understand how the surface chemical properties are influenced by the nature of the supports. Surprisingly, this is the first study to compare in depth the influence of the supports on physicochemical parameters such as acidity, site nuclearity, and reducibility. In this study, surface characterisation techniques including N₂ physisorption at -196 °C, ammonia temperature-programmed desorption, inductively coupled plasma optical emission spectrometry, temperature-programmed reduction with hydrogen, CO-chemisorption, scanning electron microscopy, transmission electron microscopy, and NO adsorption by in situ Fourier transform infrared spectroscopy have been performed to understand the different surface reactions occurring over the two different supports. The aim of this study is to ascertain the primary differences between these two catalysts using several catalyst characterization techniques and correlate their chemical and structural differences to their catalytic activity in the conversion of 2-chlorophenol. The results disclose a higher density of acid sites, a smaller particle size of iron oxide, stabilization of Fe(II) aluminate after reduction on the alumina surface, and finally, the formation of isolated iron cations on the surface of alumina which are notably absent on the silica-supported catalyst.

New Aspects on the Mechanism of C3H6 selective catalytic reduction of NO in the presence of O2 over LaFe1-x(Cu, Pd)xO3-δ perovskites

A series of LaFe(1-x)(Cu, Pd)(x)O(3-δ) perovskites was fully characterized and tested for the selective catalytic reduction (SCR) of NO by C(3)H(6) in the presence of O(2). The adsorbed species and surface reactions were investigated for mechanistic study by means of NO-temperature-programmed desorption (TPD), C(3)H(6)/O(2)-TPD, and in situ diffuse reflectance Fourier transform spectroscopy, in order to discriminate the effects of copper and palladium partial substitutions. With respect to LaFeO(3), Cu(2+) incorporation obviously improved SCR performance, due to its properties for C(3)H(6) activation with an easy generation of partially oxidized active surface C(x)H(y)O(z) species. The excellent catalytic activity at the low temperatures over LaFe(0.94)Pd(0.06)O(3) was attributed to the formation of reactive nitrites/nitrates, leading to a rapid reaction between adNO(x) and C(x)H(y)O(z) species, as well as a decreased occupation of the active sites by the inactive ionic nitrates. A mechanism was herein proposed with the formation of nitrite/nitrate and C(x)H(y)O(z) surface species and the further organo nitrogen compounds (ONCs)/-CN/-NCO as important intermediates. Moreover, the acceleration of both formation of inactive ionic nitrate and deep oxidation of C(3)H(6) contributed to a negative effect of O(2) excess for NO reduction, while Pd substitution significantly increased the O(2) tolerance ability.

SOx Storage Materials under Lean−Rich Cycling Conditions. Part I: Identification of Transient Species

The SO(x) uptake of second generation sulfur trapping materials was studied by in situ IR spectroscopy under lean-rich cycling conditions. The combination of advanced chemometric methods including generalized 2D correlation analysis, 2D sample-sample correlation analysis, and multivariate curve resolution with alternating least squares allowed the detection of the species involved in the storage process. The formation of the bulk sulfate species was always accompanied by the consumption of carbonates. The reduction of a transient surface sulfate species was identified as the key parameter in the storage process under dynamic conditions. Three distinct reaction regimes were differentiated on the industrial materials under SO(x) trapping conditions being imperceptible from conventional spectra.

In situ Infrared Spectroscopic Studies on the Mechanism of the Selective Catalytic Reduction of NO by C3H8 over Ga2O3/Al2O3: High Efficiency of the Reducing Agent

The partial oxidation of propane and the mechanism of selective catalytic reduction (SCR) of NO by propane over Ga2O3/Al2O3 in excess of O2 have been investigated using in situ Fourier transform infrared spectroscopy. An optimized Ga2O3/Al2O3 catalyst shows high activity and efficiency of the reducing agent propane (100% conversion of NO at 623 K, GHSV: 10,000 h(-1)). One molecule of propane converts more than 4 NO molecules to N2. The reaction starts with the partial oxidation of C3H8 by O2 and carboxylates (acetate, formate) are formed on the catalyst surface above 573 K. This oxidation represents the rate-determining step of the SCR reaction. These surface carboxylates represent a dominating intermediate and (easily) react with (adsorbed) NO forming nitrogen-containing organic species. The latter are proposed to react with NO to form N2. Total oxidation of propane was enhanced at temperatures above 773 K leading to decreased reductant efficiency. Surface nitrite and nitrate species can also be observed, but they were found to be spectators only. This could be concluded from the electron balance (conversion of propane relative to NO) and from the relative rates of the single reaction steps. On the basis of these investigations and stoichiometric calculations, a conclusive reaction mechanism is proposed.

On the copper oxide neutral cluster distribution in the gas phase: Detection through 355 nm and 193 nm multiphoton and 118 nm single photon ionization

The distribution of neutral copper oxide clusters in the gas phase created by laser ablation is detected and characterized through time-of-flight mass spectroscopy (TOFMS). The neutral copper oxide clusters are ionized by two different approaches: Multiphoton absorption of 355 and 193 nm radiation; and single photon absorption of 118 nm radiation. Based on the observed cluster patterns as a function of experimental conditions (e.g., copper oxide or metal sample, ablation laser power, expansion gas, etc.) and on the width of the TOFMS features, one can uncover the true neutral cluster distribution of CumOn species following laser ablation of the sample. Ablation of a metal sample generates only small neutral CumOn clusters for m less, similar 4 and n approximately 1, 2. Ablation of copper oxide samples generates neutral clusters of the form CumOm (m < or = 4) and CumO(m-1) (m > 4). These clusters are directly detected without fragmentation using single photon, photoionization with 118 nm laser radiation. Using 355 and 193 nm multiphoton ionization, the observed cluster ions are mostly of the form Cu2mOm+ for 4 < or = m < or = 10 (193 nm ionization) and CumO1,2 (355 nm ionization) for copper oxide samples. Neutral cluster fragmentation due to multiphoton processes seems mainly to be of the form CumO(m,m-1) --> CumO(m/2,m/2+1). Neutral cluster growth mechanisms are discussed based on the cluster yield from different samples (e.g., Cu metal, CuO powder, and Cu2O powder).