Study of Cs-Promoted, α-Alumina-Supported Silver Ethylene-Epoxidation Catalysts

An investigation on the role of Re as a promoter in Ag Cs Re/α-Al 2 O 3 high-selectivity, ethylene epoxidation catalysts

“…For example, Minahan and Hoflund [54] claimed Ag 3d 5 A further complication is that in some cases the oxides of silver show an anomalous negative BE shift compared to the metal. In one study [59], the Ag 2 O and AgO BE shifts were approximately 0.3 eV and 0.8 eV to lower binding energies, respectively, compared to the value of 368.2 eV for Ag o .…”

“…Previously, Minahan et al [54][55][56] claimed the main role of Cs was to act as a binder or transition layer between the Ag particles and the a-Al 2 O 3 surface which increased the strength of interaction between Ag and the support. SEM micrographs for unpromoted catalysts depicted small silver particles in addition to regions containing a thin film of Ag present on the surface of the Al 2 O 3 .…”

The influence of chemical transport via vapour phase on the properties of chloride and caesium-doped V–Fe mixed oxide catalysts in the oxidation of butadiene to furan

“…Chloride ions are assumed to play different roles in catalysed oxidation reactions such as: (i) incorporation in the surface of the catalyst, thus modifying the properties of the surface or as component of the catalytic centres as described in the case of the oxidative dehydrogenation of ethane over chloride-doped magnesia or praseodymium oxide surfaces [7,8]; (ii) oxidation to chlorine and then acting as reactant near the surface as discussed in case of the oxidative dimerisation of methane [9]; (iii) added together with an oxygen species to one of the double bonds of butadiene resulting in a structure similar to that of chlorohydrin, which could form the 1,2-epoxide able to isomerise to dihydrofuran; (iv) as carrier for components necessary for the formation of the active and selective sites by chemical transport without playing an active role as a partner in the reaction.…”

“…In some cases, chloro compounds were dosed along with the reactants to modify the catalyst surface with chloride ions [7,8]. In other cases, halides were added to the solid catalyst during its preparation [9]. Both, the modification of the catalyst properties by chloride and a participation of atomic chlorine in the gas phase reaction were discussed as reasons for the observed increase of catalytic performance.…”

“…At these temperatures, a heterogeneously catalysed reaction on the chlorinated oxide surface was assumed to play a decisive role and chloride ions are thought to influence the active centres. In an other study on the oxidative dimerisation of methane over chloride doped calcium oxide [9], it was proposed that ethane and ethene are formed by the action of the reactant oxygen at the catalyst surface under the participation of atomic chlorine in the gas phase.…”