Sander van Donk

Generation, Characterization, and Impact of Mesopores in Zeolite Catalysts

Amongst the current developments in the field of hierarchical pore structures, the creation of mesopores in zeolite crystals is the most frequently employed way to combine micropores with mesopores in one material. In this review an overview is presented of the different approaches to generate and characterize mesopores in zeolite crystals and establish their impact on the catalytic action. Mesopores can be created via several routes from which steaming and acid leaching are the most frequently applied. Novel approaches using secondary carbon templates that are removed after synthesis have recently been launched. For the characterization of mesopores, nitrogen physisorption and electron microscopy are commonly used. More recently, it was shown that electron tomography, a form of three-dimensional transmission electron microscopy, is able to reveal the three-dimensional shape, size, and connectivity of the mesopores. The effect of the presence of mesopores for catalysis is demonstrated for several industrially applied processes that make use of zeolite catalysts: the cracking of heavy oil fractions over zeolite Y, the production of cumene and hydroisomerization of alkanes over mordenite, and synthesis of fine chemicals over Y, ZSM-5, and Beta. For these processes, the mesopores ensure an optimal accessibility and transport of reactants and products, while the zeolite micropores induce the preferred shape-selective properties.

Overview and Industrial Assessment of Synthesis Strategies towards Zeolites with Mesopores

With the necessity for the refining industry to treat heavier feedstocks, there is a clear demand for improved zeolite materials displaying better accessible surface areas and higher pore volumes in order to capitalize on their effectiveness. To this end, over the last decade, there has been an intensification of research on the exploration of new routes to synthesize zeolite materials combining micropores with mesopores. Different synthesis strategies are used for their preparation (i.e., by structure breaking or so‐called ‘destructive’ pathways, or structure building or so‐called ‘constructive’ synthesis pathways). This Review discusses the variety of current synthesis strategies, while emphasizing the strengths and weaknesses of the different routes regarding material characteristics; health, safety, and environment aspects; and synthesis costs.

Zeolite Y Crystals with Trimodal Porosity as Ideal Hydrocracking Catalysts

Effektive Poren: Zeolith-Y-Kristalle mit Mikroporen (ca.u20051u2005nm), kleinen (ca.u20053u2005nm) und grosen Mesoporen (ca.u200530u2005nm) wurden aus zuvor mit Dampf und Saure behandeltem Material durch Auslaugen mit Base erhalten. Die Zeolith-Y-Kristalle mit trimodaler Porositat (siehe elektronentomographische Aufnahme) zeigen beim Hydrocracking eine nahezu ideale Selektivitat fur und erhohte Ausbeuten an Kerosin und Diesel.

Deactivation of solid acid catalysts for butene skeletal isomerisation : on the beneficial and harmful effects of carbonaceous deposits

Skeletal isomerisation of n-butene to isobutene is mainly controlled by catalyst pore topology, acid strength, acid site density and location of the acid sites. It is established that the pore structure of the catalyst is the most important feature with regard to isobutene selectivity and stability. The most favourable activity versus selectivity and stability characteristics are displayed by the zeolite ferrierite, for which the presence of carbonaceous deposits coincides with the selective performance in butene skeletal isomerisation. By-product formation, mainly propene, pentenes and octenes, as well as isobutene production initially takes place via oligomerisation and cracking throughout the ferrierite crystals. After some time-on-stream the pore system of ferrierite is largely filled by aliphatic carbonaceous deposits, with catalysis primarily occurring at the pore mouths of the channels. At this stage cracking of these aliphatic deposits is the origin of small amounts of by-products. Slowly the deposits are converted into aromatic coke, thus, further reducing reactivity and concomitant formation of non-selective products. It is emphasised that the observed increase of isobutene selectivity with time-on-stream is a consequence of the decrease of cracking reactions. Final deactivation of the catalyst is due to blockage of the pore mouth inlets by poly-aromatic compounds formed after a prolonged time-on-stream.

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.

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.