Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Patent
1997-01-08
1999-01-05
Green, Anthony
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
423593, 423594, 423595, 423598, 423599, 423600, 423604, 423605, 423606, 423607, 423608, 423609, 423610, 423617, 423618, 423622, 423624, 423625, 423631, 423632, 423633, 423635, 423639, 423643, C01B 1314, C01G 102, C01G 3102, C01G 4102
Patent
active
058558624
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the preparation of an oxide.
Inorganic oxides and especially transition metal oxides are employed in particular in the field of heterogeneous catalysis, either as inert support for catalyst or as catalyst in its entirety. Their crystal structure is often exploited in order to act as a molecular sieve.
For example, the use of zeolites which develop a crystal structure with internal channels may be mentioned. The control of the channel size provides access to specific catalysts with substrates of given size.
Access to oxides which generally have a crystal structure or a (nano)porosity which is controlled represents a considerable objective, insofar as it offers a hope of widening the field of the applications of known compounds.
The aim of the present invention is thus to propose a new access route to oxides of novel or modified structure or texture by means of simple operations making use of mild chemistry.
To this end, the subject-matter of the invention is a process for the preparation of an oxide (P), according to which (i) a solid compound (O), for example crystalline, is formed, based on an oxide containing molecular entities (1) consisting of ammoniums, diammoniums, diazaniums or diazanediums, which are substituted or otherwise, distributed within the lattice of the solid, then (ii) the entities (1) are removed from the solid (O) by reacting the compound (O) in solid phase with a gas stream including a reactant for decomposing the entities (1), and the resulting solid (P) is isolated.
The entity (1) preferably corresponds to one of the following formulae (1a), (1b) and (1c): ##STR1## in which each of R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6, which are identical or different, denotes a hydrogen atom or an alkyl, cycloalkyl or aryl radical, generally C.sub.1 -C.sub.7.
The molecular entity (1) may thus be, for example, an .sup.+ NH.sub.4 ion, an .sup.+ N.sub.2 H.sub.5 ion or an .sup.2+ N.sub.2 H.sub.6 ion.
Under the effect of the decomposition reactant the molecular entities (1) are converted into reaction products which can be easily removed from the solid which has reacted. Advantageously, a reactant which decomposes the entities (1) into light or volatile compounds which can be entrained by the said gas stream will be employed.
During stage (ii) the oxide (O) is therefore freed from the inclusions of formula (1), so that the resulting oxide (P) which is isolated is at least partially, preferably completely, free from entities (1).
Depending on the nature and the size of the radicals which it contains, the entity (1) is more or less bulky and the inclusion of this entity in the compound (O) imposes structural parameters which are a function of this bulkiness. The removal of the entity (1) from (O) by decomposition leaves more or less large unoccupied spaces in the lattice.
The characteristics of the final oxide (P) can therefore be controlled through the choice of the entity (1) which is present in the oxide (O).
The process according to the invention can be applied to the preparation of an oxide of at least one element which has a mixed valency.
The process according to the invention is preferably applied to the preparation of an oxide of at least one element (E) chosen from the group made up of true metals, transition metals and metalloids.
True metals are here intended to mean the metals of groups IA and IIA of the Periodic Classification of the elements. Sodium, potassium, rubidium, magnesium, calcium and strontium may thus be mentioned in particular.
The lanthanides and the actinides, which constitute internal transition elements, are contained within the transition metals as referred to above. Internal transition elements which may thus be mentioned are cerium, praseodymium, neodymium, samarium, europium, terbium, dysprosium, thulium, ytterbium, uranium, neptunium and plutonium.
Metalloids are intended in particular to mean the elements of group IV B, such as silicon, tin and lead, of group V B, such as phosphorus, arsenic, antimony an
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Doumerc Jean-Pierre
Grenier Jean-Claude
Petit Stephane
Green Anthony
Rhone-Poulenc Chimie
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