J. P. Hindermann

Combined infrared spectroscopy, chemical trapping, and thermoprogrammed desorption studies of methanol adsorption and decomposition on ZnAl2O4 and Cu/ZnAl2O4 catalysts

Abstract It is shown that FT-IR spectroscopy permits discrimination to be made between methoxy (methanol) and formate species adsorbed on ZnAl 2 O 4 and CuZnAl 2 O 4 catalysts. These species were found to be less stable on copper than on ZnAl 2 O 4 . The presence of reduced copper promotes methanol transformation into formates and then into C0 2 : (i) FT-IR results show that copper formate formation from methanol adsorption occurs even at room temperature and that surface oxygen ion participates in its formation; (ii) chemical trapping experiments demonstrate that increasing copper percentage destabilizes formate species, while TPD experiments correlatively indicate an accelerated transformation of formate into CO 2 . Formyl species are detected by chemical trapping only at the end of the reaction and are therefore assumed not to participate in the decomposition reaction.

Mechanism of catalytic destruction of 1,2-dichloroethane and trichloroethylene over γ-Al2O3 and γ-Al2O3 supported chromium and palladium catalysts

The destruction mechanisms of C2-chlorinated hydrocarbons have been investigated. The adsorption of 1,2-dichloroethane (DCE) and trichloroethylene (TCE) on alumina and alumina supported catalysts was studied by FTIR-spectroscopy. Interpretation of the spectra suggests that the destruction of DCE occurs via HCl elimination to vinyl chloride, followed by an attack of a hydrogen and a surface oxygen on the double bond resulting in acetyl chloride. Subsequent elimination of a chloride ion gives acetaldehyde that can be further oxidized into acetate. With regard to the destruction of TCE, the spectra indicate that TCE is attacked by a basic oxygen and a hydrogen according to Markovnikov’s rule. This results in the formation of acyl chloride, which is further converted into acetate like species. In addition, the oxidation of TCE was examined over alumina supported catalysts. While alumina itself is not very active, palladium and chromium containing catalysts are. In the absence of water, the formation of tetrachloroethylene (PCE) was observed. Addition of water to the feed resulted in a decrease in the amount of PCE produced. Although water did not affect the TCE conversion over palladium it inhibited the oxidation reaction over chromium oxide. The activity of the chromia catalyst compared to alumina might be due to the supply of basic oxygen which can attack the double bond. The inhibitive effect of water on the conversion of TCE is probably due to blocking of active oxygen sites.

Methanol synthesis on Cu/ZnAl2O4 and Cu/ZnOAl2O3 Catalysts: Influence of carbon monoxide pretreatment on the formation and concentration of formate species

Abstract Chemical trapping, thermoprogrammed desorption (TPD) and FT-IR spectroscopy have been used to study the mechanism of methanol synthesis on Cu/ZnAl 2 O 4 and Cu/ZnO Al 2 O 3 catalysts. Pretreatment of the catalyst by carbon monoxide creates anionic vacancies and increases the amount of surface formate species. Three kinds of formate are formed as characterized by FT-IR spectroscopy and TPD. One is the formate located on copper; another, which desorbs at a temperature between copper formates and formates located on ZnAl 2 O 4 , is assumed to be formed in the vicinity of an oxygen vacancy. The third is located on ZnAl 2 O 4 . Implications of these results on the reaction mechanism are discussed.

Higher alcohols synthesis from CO+2H2 on cobalt-copper catalyst. Use of probe molecules and chemical trapping in the study of the reaction mechanism

Abstract The mechanism of formation of higher alcohols has been studied by chemical trapping and probe molecule experiments on Co Cu model catalysts. The alcohol formation proceeds through the addition of a C1HaOb (a=0 or 1, b=1 or 2) entity to a hydrocarbonated group CxHy (x ⩾ 1).The migratory insertion of carbon monoxide is a possible mechanism although the addition of a formyl or a formate cannot be excluded.

Synthesis of c1 to c5 alcohols by co+h2 reaction on some modified iron-catalysts

Abstract The influence of some additives on the activity and selectivity of iron/SiO2 and iron/copper/SiO2 catalysts was studied. The adding of rare earth oxides has three principal effects, increasing the total conversion, enhancing the alcohol selectivity and raising the ethanol selectivity. The effect of Vb and VIb group metals is essentially to increase the alcohol selectivity. A reaction mechanism is proposed for the supplementary ethanol formation.

Promoting effects of lithium on Pd/CeO2 catalysts in carbon monoxide-hydrogen reactions. Chemical trapping and temperature-programmed desorption studies

At a low percentage, lithium (0.15%) increases the methanol activity and selectivity of a Pd/CeO2 catalyst. Higher lithium loadings result in the appearance of ethanol (23.4% ethanol selectivity on 3% Pd-1% Li/CeO2) but with a decreased overall catalytic activity. The maximum amounts of surface formyl species and of adsorbed carbon monoxide correspond to the most active methanol synthesis catalyst (3% Pd-0.15% Li/CeO2). These results suggest that lithium can stabilize adsorbed carbon monoxide and surface formyl species. An increase in the temperature of desorption of carbon monoxide after carbon monoxide-hydrogen reaction (from 470 to 590 K) is attributed to an interaction between adsorbed CO and Li+. This interaction can both favour carbon monoxide dissociation and carbon monoxide insertion reactions. Temperature-programmed desorption after ethanol adsorption was performed and a mechanism of ethanol formation is proposed.

Obtaining tungsten carbides from tungsten bipyridine complexes via low temperature thermal treatment

Tungsten carbides were prepared by thermal treatment under nitrogen of a tungsten bipyridine complex. The catalysts obtained have been characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), temperature programmed reduction (TPR) and elemental analysis. The reaction with 2-methylpentane was used as a chemical probe for the formation of tungsten carbide.

Formation of C2 oxygenates on rhodium-containing catalysts during CO + H2 reactions. FTIR study of acetaldehyde adsorption

The adsorption of acetaldehyde on promoted and unpromoted Rh/Sio2 catalysts has been studied. The use of labelled compounds and the adsorption of acetic acid and crotonaldehyde allowed the unambiguous identification of an acetyl species on the promoted catalysts. The mechanism of C2-oxygenate formation and the role of the promoters are discussed.

Orientation towards alcohols in CO, H2 reactions on some iron catalysts

Adding rare earths like dysprosium or lanthanum to silica-supported iron or iron-copper catalysts enhances the formation of C1 to C5 alcohols and the total conversion in CO−H2 reactions. Copper rises the alcohol orientation and also the reactivity.AbstractДобавляя редкоземельные элементы, такие как диспрозий и лантан к железным или железно-медным катализаторам на носителе SiO2 увеличивается образование спиртов от C1 до C5, а также увеличивается суммарная конверсия в реакциях CO−H2. Медь повышает ориентацию спирта, а также реактивность.

Oxidizing properties of alumina towards alcohols. Possible reaction scheme

By chemical trapping, an acyl species has been evidenced in the oxidation of alcohols to carboxylate on an alumina surface. A possible reacton scheme is discussed.AbstractС помощью химического захвата удалось доказать образование ациловых частиц при окислении спиртов до карбоксилатов на поверхности окиси алюминия. Обсуждается вероятная схема реакции.