Tuning zeolite properties for highly efficient synthesis of propylene from methanol

Series of nanosized ZSM-5 samples is synthesized at 170 °C, 150 °C, 120 °C and 100 °C. Experimental data show that the decrease of crystallization temperature leads to significant changes in zeolite properties. Crystals synthesized at 100 °C exhibit many framework defects with lower acid sites density, strength and larger external surface area. The selectivity to light olefins and the propylene-to-ethylene ratio increases as the crystallization temperature decreases. Propylene-to-ethylene ratio above 6 with the highest selectivity to propylene of 53 % is obtained over ZSM-5 catalyst prepared at 100 °C. Stability of the nanosized zeolite in MTO is also improved compared to industrial sample with similar Si/Al ratio. This catalytic performance is a result of the decrease in the acid sites density, strength and the crystals’ size, providing shorter diffusion path and larger external surface area. The presence of structural defects and different external surface are of the crystals has been shown to play an important role in the MTO catalyst performance

Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature

Methane activation and utilization are among the major challenges of modern science. Methane is potentially an important feedstock for manufacturing value-added fuels and chemicals. However, most known processes require excessive operating temperatures and exhibit insufficient selectivity. Here, we demonstrate a photochemical looping strategy for highly selective stoichiometric conversion of methane to ethane at ambient temperature over silver–heteropolyacid–titania nanocomposites. The process involves a stoichiometric reaction of methane with highly dispersed cationic silver under illumination, which results in the formation of methyl radicals. Recombination of the generated methyl radicals leads to the selective, and almost quantitative, formation of ethane. Cationic silver species are simultaneously reduced to metallic silver. The silver–heteropolyacid–titania nanocomposites can be reversibly regenerated in air under illumination at ambient temperature. The photochemical looping process achieves a methane coupling selectivity of over 90%, a quantitative yield of ethane of over 9%, high quantum efficiency (3.5% at 362 nm) and excellent stability

Desilication of highly siliceous zeolite ZSM-5 with NaOH and NaOH/tetrabutylamine hydroxide

The results of both chemical and XPS analysis pointed out that desilication of highly siliceous ZSM-5 of Si/Al = 164 was more effective in the surface zone than in the bulk, contrary to zeolite ZSM-5 of Si/Al = 31.6. According to the IR studies in parent zeolite the concentration of protonic sites was very close to the concentration of Al indicating that all Al atoms can form Si-OH-Al. The results of our quantitative IR studies strongly support the realumination thesis, i.e. some Al atoms extracted in basic solutions are subsequently reinserted forming new acidic hydroxyls. In desilicated zeolites all Al atoms were able to form protonic sites, however part of them dehydroxylated during the activation of zeolite producing Lewis acid sites according to the stoichiometry: one protonic site was transformed into one Lewis site. Low temperature nitrogen adsorption revealed that the alkaline treatment of highly siliceous zeolite with 0.2 M NaOH/TBAOH mixture produced mesopores of smaller diameter and narrower pore size distribution than in the case of zeolite of medium Si/Al ratio. This result can be explained by low concentration of Al which similarly as TBA(+) cations plays the role of pore directing agents (PDA). Contrary to TEA(+), the presence of Al in desilication mixture, led to the formation of larger pores. Therefore, in highly siliceous zeolite TBA(+) played dominant role as PDA producing narrower pores. Highly siliceous zeolite with uniform distribution of relatively narrow pores may be useful catalyst or catalyst support. The influence of desilication temperature on porosity development was also investigated. The increase of desilication temperature from 338 to 353 K resulted in both more extensive demetalation (more Si and Al is extracted) and the distinct increase of the volume and surface of mesopores. Both lower concentration of protonic sites and higher concentration of Lewis sites confirmed partial zeolite destruction upon desilication at elevated temperature. The experiments of pivalonitrile sorption followed by IR spectroscopy showed a significant increase of accessibility of acid sites to bulky pivalonitrile molecules. (C) 2012 Elsevier Inc. All rights reserved.The research was partially carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (Contract No. POIG.02.01.00-12-023/08).Sadowska, K.; Góra-Marek, K.; Drozdek, M.; Kustrowski, P.; Datka, J.; Martínez-Triguero, J.; Rey Garcia, F. (2013). Desilication of highly siliceous zeolite ZSM-5 with NaOH and NaOH/tetrabutylamine hydroxide. Microporous and Mesoporous Materials. 168:195-205. https://doi.org/10.1016/j.micromeso.2012.09.033S19520516

Generation of quantum dots at the semiconductor surface for photoreforming of biomass to CO

International audienc

In Deactivation of catalyst – can we take advantage of it?

International audienc

METAL - IODIDE CATALYTIC SYSTEM FOR DIRECT ETHERIFICATION FROM ALDEHYDES AND / OR KETONES

A process for etherification of aldehydes and / or ketones in the presence ofa catalyst and an iodine source . In particular, a process for the synthesis of an ether compound, comprising reacting an aldehyde and / or a ketone with an alcohol , in the presence of ( i ) a metal/support heterogeneous catalyst and an iodine source , or ( ii ) a metal - iodine catalyst , in a reactor, whereby the ether compound is obtained . A catalytic system comprising a metal/support heterogeneous catalyst and an iodine source , and a process for its preparatio