Catalytic deuterium exchange reactions with organics. XII. Further studies in platinum catalyst preparation-the process of self-activation

1965 ◽  
Vol 18 (7) ◽  
pp. 993 ◽  
Author(s):  
JL Garnett ◽  
WA Sollich
Keyword(s):  
Active Sites ◽  
Catalyst Deactivation ◽  
Platinum Catalyst ◽  
Platinum Oxide ◽  
Deuterium Exchange ◽  
Hydrogen Gas ◽  
Distribution Data ◽  
Exchange Reactions ◽  
Π Complex ◽  
Distribution Studies

A new process for the activation of platinum oxide, termed self-activation, is described. This procedure involves the reduction of platinic oxide with an organic compound such as benzene, naphthalene, or n-octane. The potential of the resulting catalyst in deuterium exchange reactions has been evaluated with three characteristic organic compounds, n-octane, naphthalene, and benzene. A comparison has been made in the properties of prereduced catalysts prepared by a self-activation procedure and catalysts activated conventionally with hydrogen gas. For high-temperature exchange reactions ( >90�), the former catalysts are to be preferred since higher final activities of up to 300% may be achieved. The kinetics of self-activation suggest that catalyst deactivation by reagents may be due to modification of active sites. With aromatic compounds, it is proposed that this deactivation occurs through a π-complex interaction. Isotope distribution studies in the labelled benzenes indicate that self-activated, prereduced catalysts, by comparison with hydrogen-activated catalysts, exhibit relatively low M values in relation to their activities. Distribution data are consistent with the explanation that catalyst deactivation by benzene is a process involving the generation of new types of active sites which are more numerous but of lower activity than the original sites. Attempts to stabilize prereduced catalysts by chemical methods were unsuccessful.

Catalytic deuterium exchange reactions with organics. XXVII. The alkylbenzenes on self-activated Group VIII transition metals

1966 ◽  
Vol 19 (12) ◽  
pp. 2299 ◽  
Author(s):  
BD Fisher ◽  
JL Garnett
Keyword(s):  
Transition Metal Oxides ◽  
Exchange Process ◽  
Kinetic Studies ◽  
Platinum Oxide ◽  
Activation Process ◽  
Group Viii ◽  
Exchange Reactions ◽  
Π Complex ◽  
Cis And Trans ◽  
In Cis

Exchange reactions between heavy water and the alkylbenzenes have been investigated on the following self-activated Group VIII transition metal oxides: PtO2,2H2O; PdO; Rh2O3; IrO2,2H2O; RuO2,H2O; ReO2; and Ni2O3. All oxides except Ni2O3 are self-activated by benzene up to 180�. Order of ease of self-activation is Pt > Pd > Rh, Ru, Ir > Re > Ni. Trends in deuteration rates of the alkylbenzenes on self-activated platinum oxide are generally similar to those obtained on hydrogen prereduced platinum. At 130�, some differences in reactivity are observed and these are attributed to reagent displacement effects from the presence of small percentages of dimer (1%) associated with the self-activation process. Compared with hydrogen prereduced catalysts, significant differences in isotope orientation are observed with certain alkylbenzenes on self-activated catalysts. Multiple deuteration effects which are accentuated on self-activated catalysts have been used to confirm isotope orientation and also the participation of a π-complex mechanism for the exchange process. Isomerization and exchange in cis- and trans-stilbenes on self-activated platinum have also been interpreted by the dissociative n-complex substitution mechanism. The advantages of self-activated catalysts in general deuterium and tritium labelling work have been evaluated. Possible correlations between exchange results and electron spin resonance data for charge-transfer adsorption on the above oxides are discussed. Preliminary kinetic studies with self-activation are also reported.

Hydrogen—deuterium exchange reactions on ion-exchanged X-type zeolites

1971 ◽  
Vol 321 (1545) ◽  
pp. 249-257 ◽  
Keyword(s):  
Active Sites ◽  
Large Range ◽  
Deuterium Exchange ◽  
Water Molecules ◽  
Hydrogen Treatment ◽  
Residual Water ◽  
Hydrogen Deuterium Exchange ◽  
Exchange Reactions ◽  
Hydrogen Deuterium ◽  
Homolytic Dissociation

The hydrogen—deuterium exchange reaction has been studied over a series of X-type zeolites. With CoX zeolites the activity depended linearly on the extent of ion-exchange showing that the Co 2+ ions do not enter preferentially the positions which are likely to be inaccessible to the reacting molecules. Enhanced activity was found after hydrogen treatment of CoX at 200 °C or CaX and MnX at 300 °C and to a lesser extent at temperatures about 50 K lower. This increase in activity was thought to arise from the displacement of water molecules from the active sites by chemisorbed hydrogen. Other evidence for the poisoning effects of residual water was obtained from the variation in the activity of a CoX zeolite with outgassing temperature. There was no correlation between activity and charge on the metal ions—CeX was only slightly more active than NaX and there was a large range in the activity of the zeolites containing different divalent ions (Ni ⪢ Zn > Co > Mn > Ca). It is possible that NiX, the only catalyst giving high rates below 0 °C, brings about the exchange by a mechanism involving the homolytic dissociation of hydrogen. The results show that the usefulness of deuterium for the study of the exchange reactions with hydrocarbons may be limited to a few of the more active zeolites such as NiX and possibly ZnX or CoX.

Catalytic deuterium exchange reactions with organics. XXXI. Accelerative effects of ionizing radiation and ultraviolet light on self-activated platinum oxide

1967 ◽  
Vol 20 (11) ◽  
pp. 2415
Author(s):  
JL Garnett ◽  
A Rains ◽  
PK Wong
Keyword(s):  
Ultraviolet Light ◽  
Diphenyl Ether ◽  
Platinum Oxide ◽  
Exchange Reactions ◽  
Pressure Source ◽  
Exchange Processes ◽  
Radiation Sources ◽  
Π Complex ◽  
Radiation Induced ◽  
Γ Rays

The effect of preirradiation with γ-rays from cobalt-60 and ultraviolet light from a low-pressure source on the exchange between benzene and heavy water in the presence of self-activated platinum oxide has been studied. Both rates of multiple and stepwise exchange processes are accelerated under these conditions. Of 14 oxides examined, including the Group VIII transition metals, platinum is the only one to catalyse exchange up to 130�. Preliminary experiments indicate that radiation-induced oxygen desorption from the surface of the oxide is responsible for the accelerative effect. Internal radiation sources such as tritium oxide also increase initial exchange rates. Cholesterol, naphthalene, dibenzyl, diphenyl, benzoic acid, and diphenyl ether have been studied with tritium oxide. The results can be rationalized in terms of π- complex mechanisms for exchange. A catalytic model for the mechanism of the radiation-induced effect is proposed.

Deuterium Exchange Reactions with Substituted Aromatics. III. Heterocyclics and Polycyclic Hydrocarbons

1962 ◽  
Vol 15 (1) ◽  
pp. 56 ◽  
Author(s):  
JL Garnett ◽  
WA Sollich
Keyword(s):  
Adsorption Mechanism ◽  
Lone Pair ◽  
Deuterium Exchange ◽  
Catalyst Poisoning ◽  
Polycyclic Aromatics ◽  
Exchange Reactions ◽  
Aromatic Molecules ◽  
Π Complex ◽  
Additional Interaction ◽  
A Charge

Platinum-catalysed deuterium exchange reactions between heavy-water and polycyclic aromatics and heterocyclics have been investigated. The results confirm a charge-transfer-no-bond adsorption mechanism for catalytic chemisorption. Degree of catalyst poisoning increases with decreasing ionization potential for aromatic molecules of similar complexity, e.g., anthracene and phenanthrene. As the number of nodal planes in the bonding orbitals of the more complex polycyclic aromatics increases, a decrease is observed in catalyst poisoning. Exchange of pyridine is slower than benzene and this is attributed to an additional interaction of the pyridine molecule with the catalyst through its lone-pair of electrons. The reactivity of n-octane supports extension of the authors' π-complex chemisorption theory to molecules possessing only σ-electrons. Anisole, cyclohexane, nitrobenzene, cyclohexene, and phenyl cyanide exchange in an anomalous manner.

Catalytic deuterium exchange reactions with organics. LXXI. Homogeneous platinum catalysed deuteration of the long-chain alkylbenzenes. Relationship toalkane exchange

1974 ◽  
Vol 27 (5) ◽  
pp. 1033 ◽  
Author(s):  
JL Garnett ◽  
RS Kenyon
Keyword(s):  
Deuterium Exchange ◽  
Side Chain ◽  
Exchange Reactions ◽  
Degree Of Branching ◽  
Isotope Incorporation ◽  
Π Complex ◽  
Long Chain

The long-chain alkylbenzenes out to nonylbenzene have been exchanged with D2O in the presence of homogeneous platinum, deuteration occurring in both ring and side chain. ortho-Deactivation in the ring is observed, consistent with a mechanism involving a π-dissociative process. Total isotope incorporation in a particular compound decreases with increase in length and degree of branching of the side chain. In the side chain α and terminal positions deuterata predominantly, degree of isotope incorporation in these positions decreasing gradually down the series to nonylbenzene. For butylbenzene and higher homologues, deuteration of methylene positions is low. Orientation of isotope in the side chain of l',l?-dimethylpropylbenzene is unique and is used as a basis for a novel terminal abstraction π-complex (TAPC) mechanism proposed to explain terminal exchange in the alkylbenzenes. Concepts involving 'inner' and 'outer' π-complexes are shown to be of value in discussing mechanisms of exchange in other positions of these compounds. The data may be related to mechanisms for simple alkane exchange using this same catalyst.

Catalytic deuterium exchange reactions with organics. XXXVI. The labelling of ( - )-inositol on self-activated platinum oxide with and without radiation

1967 ◽  
Vol 20 (12) ◽  
pp. 2647 ◽  
Author(s):  
SJ Angyal ◽  
CM Fernandez ◽  
JL Garnett
Keyword(s):  
Tritiated Water ◽  
Platinum Oxide ◽  
Deuterium Exchange ◽  
Exchange Reactions ◽  
Catalytic Method ◽  
Experimental Conditions ◽  
Extensive Degradation

Exchange of (-)-inositol with curie levels of tritiated water on self- activated platinum oxide leads to incorporation of tritium of which 92.5% is found at C l and C 6, 3.7% at C 2 and C 5, and 3.8% at C 3 and C 4. Isotope scavenging indicates that inversion occurs only at C1 yielding labelled myoinositol. Exchange is accelerated in the presence of u.v. light without extensive degradation. A comparison has been made between the Wilzbach gas irradiation technique and the catalytic method for labelling (-)-inositol. Possible mechanisms for tritium incorporation in (-)-inositol are discussed for the various experimental conditions used.

Sign in / Sign up

Export Citation Format

Share Document