Thomas Turek

The Catalytic Hydrogenolysis of Esters to Alcohols

Abstract The hydrogenolysis of esters to alcohols is a reaction between esters and hydrogen which selectively splits a C-0 bond adjacent to a carbonyl group (1). A well-known large-scale industrial process based on this reaction the production of fatty alcohols from natural fatty acid esters-has been operated commercially for more than 50 years. Several processes which include the hydrogenolysis of an ester have been proposed for the manufacture of basic chemicals such as methanol and ethanol. Furthermore, there has been continuous interest over the past two decades in replacing the existing, energy-intensive processes for the production of ethylene glycol and 1,4-butanedioI by more cost-effective routes involving ester hydrogenolysis. While particular aspects of the literature on hydrogenolysis of esters have been reviewed already [1–3], the objective of the present work is to give a more general summary with special emphasis on the present or possible industrial applications of ester hydrogenolysis.

Preparation of a highly active Fe-ZSM-5 catalyst through solid-state ion exchange for the catalytic decomposition of N2O

Abstract This work describes a new and simple preparation method for Fe-ZSM-5 pentasil-zeolites through solid-state ion exchange process. The zeolite catalysts thus prepared exhibit high activity during the catalytic decomposition of N 2 O in the absence of reducing agents. The aimed choice of using FeSO 4 ×7H 2 O and NH 4 -ZSM-5 as starting materials consisted of forming such products (ammonium salts) after the ion exchange process that can be completely removed through thermal treatment. The complete preparation process leading to the formation of catalytically active iron species inside the zeolite takes place in two steps at two distinguished temperatures, respectively. The first step during which the solid-state ion exchange takes place has been carried out through two different routes, in air and in vacuum, in search for an enhanced catalytic activity. The second step has to be necessarily done under anaerobic conditions. XRD measurements have revealed the presence of hematite in samples with a Fe(II)/Al ratio above 0.5. The different numbers of Bronsted sites occupied by the iron species in the catalysts with different Fe contents have also been determined.

Simultaneous catalytic reduction of NO and N2O using Fe-MFI prepared by solid-state ion exchange

Solid-state ion exchange in the presence of air has been used to prepare Fe-MFI catalysts that exhibit activities comparable to preparations obtained under anaerobic conditions. Preliminary results obtained during the simultaneous catalytic reduction of NO and N2O with propane in the temperature range from 473 to 773 K show that Fe-MFI might be of interest for the treatment of exhaust gases containing NOx and nitrous oxide. Undesirable CO formed in a side-reaction can be oxidized to CO2 by promotion of Fe-MFI with small amounts of Pt.

Isothermal oscillations in the catalytic decomposition of nitrous oxide over Cu-ZSM-5

The catalytic decomposition of nitrous oxide was studied on a copper-exchanged ZSM-5 catalyst in the temperature range 648–723 K. Using a mixture of 1000 ppm N2O in nitrogen, isothermal oscillations both in nitrous oxide and oxygen concentrations occurred, accompanied by formation of small amounts of NO. While the addition of excess oxygen did not significantly change frequency and amplitude of the oscillations, even the presence of small amounts of NO immediately quenched the oscillations. The reacting system then remained in the ignited state at high nitrous oxide conversions.

Intrinsic kinetics of nitric oxide reduction by ammonia on a vanadia-titania catalyst

Abstract The kinetics of the selective catalytic reduction of nitric oxide by ammonia on a vanadia-titania (anatase) model catalyst have been investigated. Stationary values of the reaction rates are measured as a function of the concentrations of NO, NH3 and H2O in a recirculation system. Up to values usually present in flue gases the water content only weakly affects the rate of the main reaction, the reduction of nitric oxide to nitrogen. On the other hand the possible side reactions, the oxidation of ammonia and the formation of nitrous oxide are largely suppressed by the presence of water. The investigation of transport phenomena has shown that a strong influence of inner mass transfer resistance is expected in catalysts of technically relevant dimensions. The intrinsic kinetics can be quantified by use of a Lang-muir-Hinshelwood type rate equation.

Hydrogenolysis of Dimethyl Maleate on Cu/ZnO/Al2O3 Catalysts

The gas-phase hydrogenolysis of dimethyl maleate at 10 bar and 513 K was investigated over a series of co-precipitated Cu/ZnO/Al 2 O 3 catalysts. High copper surface areas were obtained with a molar Al content of 5% in the catalysts. Upon variation of composition at fixed alumina content, copper surface areas increased until the molar ratio exceeded Cu/Zn=2:1. At the given reaction conditions, dimethyl maleate was completely converted to dimethyl succinate, which further reacted to methanol, γ-butyrolactone, tetrahydrofuran, and water over all catalysts. Initial deactivation of catalysts was mainly caused by a loss of copper surface area. The catalyst with a molar Cu/Zn ratio of 1:2 was found to be most active and stable under reaction conditions.

Catalytic combustion in a reactor with periodic flow reversal. Part 1. Experimental results

Abstract The use of a reactor with periodic flow reversal for catalytic incineration of the model pollutants carbon monoxide and propane has been experimentally studied. The mean axial temperature profile over one period in cycle steady state is a symmetrical curve which can be linearised and subdivided into three regions. The center of reactor with a constant maximum temperature and two reactor ends with a linear temperature profile. The most important parameters influencing the reactor operation were found to be catalytic activity, adiabatic temperature rise (reactant concentration) and heat transfer properties of the fixed bed. Higher catalytic activity leads to a decrease of the maximum temperature profile. Increasing reactant concentrations cause higher values of maximum temperature, temperature gradient in the reactor ends and mean temperature at reactor inlet/outlet. A higher number of heat transfer units as a measure for the heat transfer characteristics of the catalyst bed give rise to higher maximum temperature and higher temperature gradient in the reactor ends, while the mean temperature at reactor inlet/outlet remains constant. Investigation of the ignition and extinction behavior of the reactor has shown that a fixed bed with a lower number of heat transfer units requires higher reactant concentrations to maintain stable operation in the ignited state.

Kinetics of nitrous oxide decomposition over Cu-ZSM-5

Abstract The kinetics of nitrous oxide decomposition on an overexchanged Cu-ZSM-5 catalyst were measured using a gradientless reactor. Isothermal oscillations of nitrous oxide and oxygen concentrations can be observed in a broad range of experimental conditions. A transition of the catalytic activity during oscillations is accompanied by a change in the oxygen content of the catalyst and by the formation of traces of nitric oxide. The presence of excess oxygen does not significantly alter the behaviour of the catalyst whereas NO concentrations as low as 10 ppm quench the oscillations in the whole temperature range studied (375 to 450°C), maintaining steady-state operation at maximum catalytic activity. Reaction rates in this ‘ignited’ state are first order with respect to nitrous oxide concentration and not affected by either oxygen or nitric oxide. At temperatures above 400°C, the observed reaction rates are influenced by pore diffusion effects. In the region of intrinsic kinetics, the temperature dependence of the first order rate constant can be described by an activation energy of ca. 100 kJ/mol.

Hydrogenolysis of dimethyl succinate on copperbased catalysts

Abstract The gas-phase hydrogenolysis of dimethyl succinate ( DMS ) has been studied over a series of copper-based catalysts at a temperature of 513 K and a pressure of 500 kPa. Using copper chromite and copper on silica, γ-butyrolactone (GBL) and methanol were formed in the first step, while GBL reacted further to tetrahydrofuran (THF) and water. Over copper zinc oxide catalysts, THF was mainly formed in a parallel reaction directly from DMS. Additionally, the steam reforming of methanol occurred over these catalysts. No catalyst deactivation with time-on-stream could be detected, but exposure to DMS significantly decreased the copper surface area of all catalysts. The area specific rate for the reaction of dimethyl succinate to γ-butyrolactone over copper zinc oxide was one order of magnitude higher than over the other catalysts. The most active catalyst for the subsequent reaction of GBL to tetrahydrofuran was found to be copper chromite. The reaction rates could be described by simple kinetic equations based on a reaction network.

The formation of HCN during the reduction of NO by isobutane over Fe-MFI made by solid-state ion exchange

FTIR analysis of the gaseous products of the selective catalytic reduction of NO by isobutane over a Fe‐MFI catalyst made by solid‐state ion exchange shows, for the first time, that HCN can be a substantial product. Under dry conditions the amounts formed can exceed that of N2 for temperatures up to 280°C and NO conversions of 25% with a maximum HCN concentration of∼150 ppm formed at 315°C. However, introduction of 0.7% water causes the subsequent conversion of about one‐half the HCN to N2, probably through hydrolysis to NH3 and the NH3‐SCR reaction which is very rapid on Fe‐MFI. The steps through which HCN forms remain to be established.