Zeolite catalysis

N21

came

depleted.

reactor

However,

the selectivity

in a fixed-bed

did not vary once

complete

oxygen

achieved.

These and other considerations

conversion

led Durante to develop methane

a mechanism

dehydrogenation

a catalyst

surface

bond to generate cal. The general

desorbable approach

that might generate

methyl radi-

centres on ac-

metal 0x0 centres

ming a surface hydroxyl has synthesized

group.

The Sun of inor-

iron sodalite

coferrates

high-oxi-

iron 0x0 species.

cited by Durante include stituted

isolated

multinuclear

a predominantly

Examples

framework

and amorphous

containing

or oxo-bridged

by for-

a variety

ganic catalysts that can generate dation-state

for

the C-H

alkyl radicals

subsili-

iron atoms

iron centres in

siliceous framework.

Sodium-exchanged

iron sodalite

con-

tanning 13% iron seems to be a promising

Hutchings,

Van

Rensburg,

paper on liMethan carbons

to Hydro-

Further Evidence

for the Role of NO”. In this they present some new information troversy

relating to the con-

over the involvement

cals in the conversion

of free radi-

of methanol

soline. They conclude

NO inhibits the reaction is because it reacts with a methyloxonium

intermed~ateto

after rearrangement,

a strongly

A second paper concerned is on the “Flexibility

with zeolites

in Zeolites:

Studies

of ZSM-5

Conner,

Vincent,

sorption

of molecules

by

Man and Fraissard.

Ad-

whose

dimensions

are similar to the pore dimensions changes

orthorhombic.

qua~z-lined aneiairfeed

reactors.

With a 3 to 1 meth-

in the quartz reactor, the selec-

tivity to methanol conversion.

was 70% at 7% methane

There is currently a keen inter-

est in the development conversion version

in

of processes for the

of methane and the direct con-

of methane

to methanol

ually being seen as a promising

is gradroute.

In this paper

and discuss ratio

treatment

of the

and

with organic

synthesis.

is concerned

Climent,

Garcia,

Primo and Corms describe the use of “Zein Organic Condensati~fl

phenone with Benzaldehyde”. between acetophenone

Reactions. of AcetoThe reaction

and benzaldehyde

results in the formation of chaicones, Zeolites catalysts

are

~mpo~ant

and this is reflected

and

versatile

in the latest

by steam

(impo~ant).

A third paper on zeolites

Claisen~S~hmidt

Zeolite Catalysis

of

with

modification

(unimportant)

olites as Catalysts K. SESHAN

the authors

temperature

(important),

phosphorus

to

for the flexibility

the impo~ance

regard to the transition Si/Al

in ZSM-5,

from monoclinic

provide further evidence zeolites

induces

in the solid structure. The effects

cant methanol

and it was

*‘Si NMR

Frame Transitions”

can be quite large. For example,

the experiments

form,

bonded

oxime, leading to catalyst deactivation.

the crystals transform

decomposition,

to ga-

that the reason why

catalyst for the reaction, The stainless steel

to perform

Copper-

Conversion

over H-ZSM-5:

walls of the reactor system induced signifinecessary

Cata-

lysis. thwaite, Hunter, Dwyer and Dewing have a

which involves

that cleaves

tive surfaces containing

group

had been

be of interest to readers of Applied

are impo~ant

intermediates

thesis of naturally

occurring

which

in the

syn-

heterocyclic

issue of Catalysis Letters (Volume 4, No. 1)

compounds

which contains three papers on very differ-

port on the use of large pore HY zeolites as

ent aspects of zeolite catalysts which may

~atalystsfor

applied catalysis -

Volume 59 No. 2 -

2 April 1998

In this paper the authors

re-

this reaction. They find that HY

N22

zeolites catalyse this reaction in the liquid phase at modaratetemperatures. The authors believe that there are many other opportunities for zeolites, clays, etc. to be used as catalysts under mild conditions for general synthetic organic reactions There would appear to be a number of interesting opportunities here for catalyst chemists to collaboratewithsyntheticorganic chemists to the mutual benefit of both,

Annual Review of Physical Chemistry The latest issue of the Annual Review of Physical Chemistry, Volume 40 (1989), has no articles directly related to aspects of catalysis - indeed the last catalytic review appeared several years ago (D.W. Goodman, Ann. Rev. Phys. Chem., 37 (1986) 425). Nevertheless there are several articles in the current issue which the wellread practitioner of catalysis must look at: “Picosecond vibrational energy transfer studies of surface adsorbates” by E.J. Heilwell, M.P. Casassa, RR. Cavanagh and J.C. Stephenson, p. 143. “Fundamental mechanisms of desorption and fragmentation induced by electronic transitions at surfaces” by P. Avouris and R.E. Walkup, p.173. “Theory of adsorbate interactions” by P.J, Feibelman, p. 261. “Transition metal oxides” by C.N.R. Rao, p. 291. “Atomic~resoi~ion surface spectroscopy with the scanning tunne~ling microscope” by R.J. Hamers, p. 531. A New Experimental Kinetic Studies

Method for

The principle of using a small but fast perturbation of a system at equilibrium to

applied catalysis -Volume

59 No. 2 -

determine the kinetics of reversible changes has been with us for a long time. In the past decade a version of it, the frequency response method, has been developed and used by Y. Yasuda, of‘royama Universjty~ Japan, and I.V.C. Rees, of Imperial College, London, to determine mass transfer and adsorption kinetics, especially with zeolite adsorbents. Yasuda has now extended the technique for the study of the kinetics of a heterogeneous catalytic reaction (J, Phys. Chem., 93 (1989)7185). As in the adsorption studies the total volume of the system (reacting gas plus catalyst) is changed sinusoidally by typically 2 10% or less by motor-driven bellows The frequency of oscillation can be varied over a very wide range in most applications of the method, so giving access to kinetic phenomena of differing time constants. The pressure of the system is followed by a fast-response pressure sensor. The calculation of the kinetic parameters from amplitude and phase-lag angle and their variation with oscillation frequency is now well established. Clearly the system is more comptex when catalysis takes place. Yasuda uses the hydrogenation of propene over a platinum/alumina catalyst at 273 K with each partial pressure at ca. 1ClPa. The apparatus was operated as a flow reactor and changes in each partial pressure were followed by mass spectrometry. Thusthe perturbations were to a steady state rather than an equ~iibrium state. Yasuda calculates the order of reaction to be 0.15 and derives a rate constant of 0.15*10-2 min-‘. It is too early to assess the value of this method for catalytic studies, especially in relation to other techniques using transients, but it seems to have the potential to be a another weapon in the armoury of the catalytic worker.

2 April 1990