Reinhard Eckelt

Spectroscopic and physicochemical characterization of P-Modified H-ZSM-5

Acidic properties of P-modified H-ZSM-5 have been characterized by means of ammonium exchange, temperature-programmed desorption of ammonia (NH3 TPD), as well as IR, 27Al MAS NMR, and 31P MAS NMR spectroscopy. The introduction of phosphorus by impregnation of the zeolite with an aqueous solution of orthophosphoric acid decreases the number of Bronsted acid sites. Bronsted acidity can be restored completely by elution of the orthophosphoric acid with hot water. Only after calcination or steaming at elevated temperatures of the H3PO4-impregnated sample is an irreversible decrease of Bronsted acidity caused by dealumination observed. The formation of aluminum phosphates in nonframework positions proceeds simultaneously. Thermal treatment of H3PO4-impregnated H-ZSM-5 results in degrees of dealumination lower than those with non-impregnated samples, indicating that phosphorus partially protects aluminum ions from being removed from their substitutional positions in the silica framework.

Low-temperature conversion of NOx to N2 by zeolite-fixed ammonium ions

Abstract The selective catalytic reduction (SCR) of NOx in oxygen excess is reported to proceed with good efficiency by NH4+ ions fixed to zeolites at temperatures as low as 373 K. The reaction starts with almost complete reduction of NOx to N2 under consumption of NH4+ ions thereby converting the zeolite into its H+ form. The consumed NH4+ ions can easily be replenished at reaction temperature by admission of gaseous ammonia. A key step of the reaction sequence is the oxidation of NO to NO2 by O2 which is catalyzed by the zeolite. Both properties of the zeolite, namely, its storage capacity for NH3 (in the form of NH4+ ions) and its oxidation capability for NO allow the abatement of NOx in exhaust gases at low temperatures and in the presence of oxygen without permanent addition of a reductant. This process is named catalytic low temperature conversion (CLTC) of NOx.

Comparison of mesoporous silica and alumina supports for palladium-catalyzed carbon–carbon coupling reactions: unexpected high acceleration by supported cetyltrimethylammonium bromide

The coupling reaction of p-iodoanisole and phenylboronic acid occurs with high yields in aqueous medium in the presence of palladium complexes with water-soluble phosphine ligands on different mesoporous inorganic supports. Silica and alumina supports were similarly prepared and functionalized with sulfonate groups. The catalyst was immobilized by ion exchange. A novel approach to the amphiphilization of the supports by cetyltrimethylammonium bromide was applied to modify phase transfer steps favorably and to embed the catalyst in this bipolar surface layer. The reaction is accelerated and conversions with these embedded catalysts exceed those in homogeneous systems.

Improvement of catalytic properties of SAPO-31 molecular sieves by using an activated form of Si02

Abstract SAPO-31 molecular sieves the synthesis of which is based on different types of SiO2 were physicochemically characterized by X-ray diffraction, IR, temperature-programmed desorption of ammonia,29Si magic angle spinning nuclear magnetic resonance and catalytically investigated in the conversion of methanol to lower alkenes and in the isomerization of n-heptane. The use of ultradispersed SiO2 generated in a capacitively coupled high frequency plasma (CCP) allowed us to synthesize SAPO-31 molecular sieves of Bronsted acidities which are higher than with samples based on traditional silicon sources. Results of the conversion of methanol and of the isomerization of n-heptane show that the use of plasma-chemically generated silica in the synthesis of SAPO type molecular sieves can be a way to improve their catalytic properties.

Catalytic properties of the gallophosphate cloverite 1 Gas-phase formation of methyl tert.-butyl ether

Abstract A viable catalytic application of the gallophosphate cloverite is reported for the gas phase etherification of isobutene to methyl-tert.-butyl ether under atmospheric flow conditions at temperatures from 363 to 383 K following appropriate decomposition of the quinuclidine template.

High-Temperature Synthesis of Ordered Mesoporous Aluminosilicates from ZSM-5 Nanoseeds with Improved Acidic Properties

Ordered mesoporous SBA-15 analogs with different Si/Al ratios were successfully prepared in a two-step process from self-assembly of ZSM-5 nanoseeds at high temperature in mildly acidic media (473 K, pH 3.5). The obtained products were characterized as SAXS, XRD, N2 sorption, FTIR, TEM, NH3-TPD, AAS and ICP. The results show that the initial Si/Al molar ratio of ZSM-5 precursors strongly affects the final materials’ properties. A highly condensed, well-ordered mesoporous SBA-15 analog with improved hydrothermal stability and acidic properties can be prepared from low aluminum containing ZSM-5 precursors (Si/Al ≥ 20). Reducing the initial Si/Al molar ratio to 10, however, leads to the formation of a disordered mesoporous SBA-15 type material accompanied by degraded textural and acidic properties. The gas phase cracking of cumene, carried out as probe reaction to evaluate Brønsted acidity, reveals that an increased density of Brønsted acid sites has been achieved over the SBA-15 analogs compared to conventional Al-SBA-15 due to the preservation of zeolite building units in the mesopore walls of the SBA-15 analogs.

A new method for the quantitative determination of zeolitic Brønsted acidity

A new method for the quantitative determination of zeolitic Bronsted acidity is proposed utilizing the specific low-temperature reaction of NH 4 + ions fixed to Bronsted sites with NO–O 2 thus preventing the loss of acid sites normally encountered for the conventional temperature-programmed mode of NH 3 thermodesorption.