Alfred Broersma

Butene skeletal isomerization over H-ferrierite: a TEOM and in situ IR study on the role of carbonaceous deposits and the location of bronsted acid sites

Butene skeletal isomerization over H-ferrierite (H-FER) is monitored in a catalysis set-up including a tapered element oscillating microbalance (TEOM) and using in situ infrared (IR) spectroscopy. For the first time the location and number of vacant Bronsted acid groups sited in the 10, 8, 6, and 5 membered rings (MRs) of the H-ferrierite framework are established as a function of time-on-stream (TOS). By deconvolution of the acid site-band, it is determined that with proceeding reaction the 8 MR channels are blocked and the available micropore volume and Bronsted acidity on the aged H-ferrierite will be primarily located inside the 10 MR channels. When a maximum amount of hydrocarbons is deposited on the catalyst, vacant Bronsted acid sites are still present. Additionally, IR spectroscopy shows that with TOS carbonaceous deposits are slowly converted from hydrogen-rich alkyl-aromatics into hydrogen-poor cyclopenta-fused-alkyl-aromatics, reducing by-product formation and therefore enhancing isobutene selectivity.

Metal catalysts supported on a novel carbon support

Abstract Carbon fibrils can be produced smoothly by exposing finely dispersed iron or nickel particles to reducing carbon containing gas flows. Alumina-supported iron particles were used to grow carbon fibrils with cylindrical graphite layers parallel to the fibril axis. The carbon fibrils interweave during growth, resulting in the formation of tangled skeins. Owing to the size of the skeins (about 3 μm), the pore volume, the pore size distribution, the surface area, the filterability and the mechanical strength, the skeins are very appropriate as supports for, e.g., noble metal particles, in liquid phase catalytic processes. Therefore, we examined the properties of the bare carbon fibrils, as, well as the properties of catalysts supported on carbon fibrils. To obtain carbon fibril-supported palladium catalysts, a homogeneous deposition-precipitation procedure was utilized. Varying preparation conditions, such as, the atmosphere during drying and the pretreatment of the carbon fibrils, affect the activity in the liquid-phase hydrogenation of nitrobenzene significantly.

Extended Structure Design with Simple Molybdenum Oxide Building Blocks and Urea As a Directing Agent

We report here a simple one-pot directed synthesis of an oxomolybdate urea composite in which elementary molybdenum oxide building blocks are linked together with the aid of urea. This type of directed material design resulted in large rod-like crystals of an inorganic-organic hybrid extended structure of {MoO 3(NH 2-CO-NH 2)} infinity consisting of right- and left-handed helical units. In the crystal structure urea acts both as a glue that links the inorganic molybdenum units into a helix and as a supramolecular linker for the stabilization of the crystal structure as a whole. This type of molecular topology resulted in an unexpectedly high thermal stability.

Unraveling the nature and location of the active sites for butene skeletal isomerization over aged H-Ferrierite

The relation between the catalytic performance, the number and location of the accessible active sites and the nature of carbonaceous deposits was established for aged H-ferrierite during n -butene skeletal isomerization. In situ infrared spectroscopy reveals that the deposition of carbonaceous species significantly lowers the number of Bronsted sites. With short time-on-stream such deposits display large reactivity and induce by-product formation but also contribute to part of the isobutene production. With prolonged time-on-stream the deposits are converted into non-reactive carbon species and accordingly isobutene selectivity is enhanced. Probing with d 3 -acetonitrile does not reveal the presence of carbenium ions at this stage. Additionally, it is established that part of the Bronsted acid sites in the 10 membered-ring channels are still accessible and most likely catalyze the selective conversion of n -butene into isobutene.

19-P-08 - Transient uptake measurements using an oscillating microbalance: effect of acid leaching on the diffusivity of n-hexane in Pt/H-mordenite

Publisher Summary This chapter presents transient uptake measurements using an oscillating microbalance. Measurements performed in a tapered element oscillating microbalance (TEOM) reveal that diffusivities can be derived from uptake data monitored under full reaction conditions. The effect of acid leaching on the diffusional behavior of n -hexane in platinum (Pt)/H-Mordenite is investigated. Acid leaching largely enhances the n -hexane uptake rate, but does not result in a net increase in the intracrystalline steady state diffusivity. The accelerated uptake after acid leaching merely arises from the shorter intracrystalline diffusion path resulting from the mesoporous structure.