CA1251432A - Layered oxides containing interlayer polymeric oxides and their synthesis - Google Patents

Abstract

LAYERED OXIDES CONTAINING INTERLAYER
POLYMERIC OXIDES AND THEIR SYNTHESIS

ABSTRACT OF THE DISCLOSURE

Catalytically active, layered oxide products of high thermal stability and surface area having interlayer pillars containing polymeric oxides, such as polymeric silica and alumina, are prepared by ion exchanging a layered metal oxide, such as a layered silicate, with organic cations, to spread the layers apart.
A first compound such as tetraethylorthosilicate, capable of forming a polymeric oxide, and a second compound, such as aluminium isopropoxide, capable of forming catalytically active sites in the interlayer pillars are thereafter introduced between the layers.
The resulting product is treated, e.g. by hydrolysis, to form the polymeric oxide, and produce the pillars between the metal oxide layers. The resulting product may be employed as a catalyst material in the conversion of hydrocarbons.

Description

3~
P0 ~ SYNTHESIS

The present invention relates to layered oxides containing interlayer polymeric oxides and to their synthesis.
Many layered materials are known which have three-dimensional structures which exhibit their strongest chemical bonding in only two dimensions. In such materials, the stronger chemical bonds are formed in two-dimensional planes and a three-dimensional solid is formed by stacking such planes on top of each other. However, the interactions between the planes are weaker than the chemical bonds holding an individual plane together. The weaker bonds generally arise from interlayer attractions such as Van der Waals forces, electrostatic interactions, and hydrogen bcnding.
~n those situations where the layered structure has electrically neukral sheets interacting with each other solely through Va~ der Waals forces, a high degree of lubricity is manifested as the planes slide across each other without encountering the energy barriers that arise with strong interlayer bonding. Graphite is an example of such a material. The silicate layers of a number of clay materials are held together by electrostatic attraction provided by ions located between the layers. In addition, hydrogen bonding interactions can occur directly between complementary sites Dn ad~jacent layers, or can be provided by interlamellar bridging molecules.
Layered materials such as clays may be modified to increase their surFace area. In particular, the distance between the layers can be increased substantially by absorption o~ various swelling agents such as water, ethylene glycol, amines and ketones, which enter the interlamellar space and push the layers apart. However, the interlamellar spaces of such layered materials tend to collapse 3~

when the molecules occupying the space are removed by, for example, exposing the clays to high temperatures. Accordingly, such layered materials having enhanced surface area are not suited for use in chemical processes involving even moderately severe conditions.
The extent of interlayer separation can be estimated by using standard techniques such as X-ray diffraction to determine the basal spacing, also known as "repeat distance" or "d-spacing".
These values indicate the distance between, for example, the uppermost margin of one layer and the uppermost margin of its adjoininQ layer. If the layer thickness is known, the interlayer spacing can be determined by subtracting the layer thicl<ness from the basal spacing.
Various approaches have been taken to provide layered materials of enhanced interlayer distance havin0 thermal stability.
Most techniques rely upon the introduction of an inorganic "pillaring" agent between the layers of a layered material. For exarnple, U.S. Patent 4,216,188 discloses a clay which is cross-linked with metal hydroxide prepared from a hir~hly dilute colloidal solution containing fully separated unit layers and a cross-linking agent comprising a colloidal metal hydroxide solution. However, this method requires a highly dilute forming solution of the clay ( ~ 19/1) in order to effect full layer separation prior to incorporation of the pillaring species, as well as positively charged species of cross linking agents. U.S. Patent 4,248,7~9 relates to stable pillared interlayered clay prepared from smectite clays reacted with cationic metal complexes of metals such as aluminurn and zirconium. The resulting products exhibit high interlayer separa-tion and thermal stability.
U.S. Patent 4,176,û90 discloses a clay composition interlayered with polymeric cationic hydroxy metal complexes of metals such as aluminum, zirconium and titanium. Interlayer distances of up to 16A are claimed although only distances restricted to about 9A are exemplified for calcined samples. These distances are essentially unvariable and depend on the specific size of the hydroxy metal complex.

3~
F-3~12 --3--Silicon-containing materials are believed to be a highly desirable species of pillaring agents owing to their high thermal stability. U.S. Patent 4,367,163, for example, describes a clay pillared with silica prepared by impregnating a clay substrate with a silicon-containing reactant such as an ionic silicon complex, e.g., silicon acetylacetonate, or a neutral species such as SiC14. The clay may be swelled prior to or during silicon impregnation with a suitable polar solvent such as methylene chloride, acetone, benzaldehyde, or dimethylsulfoxide. This method, lo however9 appears to provide only a monolayer of intercalated silica resulting in a product of small spacing between layers, about 2-3 A
as determined by X-ray diffraction.
rn a first aspect, the present invention resides in a layered product comprising a layered oxide of an element ranging ln atomic number ~rom 13 to 15, 21 to 33, 39 to ~1, 57 to 8-3 and greater than 9û, incluslve, and pillars separating the oxide layers, the pillars containing a polymeric oxide of an element selected from Group IVB of the Periodic Table and catalytically active sites and said product having a d-spacing of at least lOA.
In a second aspect, the invention resides in a layered product comprising a non-swellable layered oxide of an element ranging in atomic number from 13 to 1~, 21 to 33, 39 to 51, 57 to 83 and greater than 90, inclusive9 and pillars containing at least one polymeric oxide and catalytically active sites separating the oxide layers.
In a third aspect, the inven-tion resides in a layered silicate composition having pillars between the silicate layers, the pillars containing a polymeric oxide selected from silicon, titanium, zirconium and hafnium and further containing catalytically active sites.
In a fourth aspect, the invention resides in a method for preparing a layered product having adjacent layers separated by polymeric oxide pillars9 which method comprises starting with a layered oxide material of an element ranging in atomic number from 3;~

13 to 15, 21 to 33, 39 to 51, 57 to 83 and greater than 90, said layered oxide material having anionic sites associated therewith;
physically separating the layers of the oxide material by introducing an organic cationic species between the layers at said anionic sites; introducing between the separated layers of said layered oxide at least one compound capable of conversion to a polymeric oxide and at least one compound capable of conversion to produce catalytically active sites; and converting said compounds to produce polymeric oxide pillars containing catalytically active sites separating adiacent layers of the layered oxide material.
The method of present invention is particularly usefu~ in that it permits the preparation of catalytically active, layered oxide materials of relatively high d-spacing, e.g., greater than about lOA, preferably greater than about 2ûA, up to or even c, c, exceeding 3ûA, preferably up to 25A. These materials can be exposed to severe conditions such as those encountered in calcining wi.thout significant decrease in interlayer distance. furthermore, such layered oxides can be prepared without the severe dilution necessary to introduce the pillaring material as is often encountered in prior art techniques of interlayering. Finally, by varying the size of the organic cationic species separating the oxide layers, it is possible to form pillared products with widely varying interlayer spacing.
The method of the present invention utilizes a layered oxide starting material which has interlayer cations associated therewith. Such cations may include hydrogen ion, hydronium ion and alkali metal cations. The starting material is then treated with a "propping" agent comprising a source of an organic cation, such as an organoammonium cation, in order to effect an exchange of or addition to the interlayer cations resulting in the layers of the starting material being propped apart. The source of organic cation in those instances where the interlayer cations include nydrogen or hydronium ions may include a neutral compound such as an organic amine which is converted to a cationic analogue during the 3~

"propping" treatment. The foregoing treatment results in the formation of a layered metal oxide of enhanced interlayer separation depending upon the size of the organic cation introduced. In one embodiment, a series of organic cation exchanges is carried out.
For example, an organic cation may be exchanged with an organic cation of greater si~e, thus increasing the interlayer separation in - a step-wise fashion~ Preferably, contact of the layered oxide withthe propping agent is conducted in aqueous medium so that water is trapped within the interlayer spaces of the propped oxide.
After the ion exchange, the organic-"propped" species is treated with a compound capable of conversion, preferably by hydrolysis, to a polymeric oxide. The ~'propped" layered material containing the polymeric oxide precursor is then treated to produce polymeric oxide pillars separating the oxide layers. Where the treatment involves hydrolysis, this may for example be carried out using water already present in organic-"propped" layered oxide material.
It is preferred that the organic cation deposited between the layers be capable of being removed from the layered oxide material without substantial disturbance or removal of the polymeric oxide or oxide precursor. For example, organic cations such as n-octylammonium may be removed by calcination or chemical oxidation, preferably by calcination and preferably after the polymeric oxide precursor has been converted to the polymeric oxide.
The resulting oxide-pillared product exhibits high surface area, e.g., greater than 200, ~00, or even 600 rn2/g, and thermal stability making it useful as a catalyst or catalytic support For hydrocarbon conversion processes, for example cracking and hydrocracking.
The layered oxides used in the present invention are layered oxides of elements having an atomic number from 13 to 15, 21 to 33, 39 to 51, 57 to 83 or greater than 9û. Preferably, the layered oxide is ~'non-swellable~ which is intended to distinguish from conventional clays which contain octahedrally coordinated ~ 3 metal oxide sheets bonded to tetrahedrally coordinated silica sheets and which undergo substantial swelling, sometimes by an essentially unbounded amount, when contacted with water. As used herein in relation to a layered oxide material, the term ~non-swellable" is defined as meaning a layered oxide material which, when contacted with at least 10 grams of water per gram of the layered oxide at 23C for 24 hours, exhibits an increase in d spacing no greater than 5A as compared with the anyhydrous material. Included among these materials are H2Ti307, Na2Ti307 and KTiNbO5 as well as certain layered silicates, for example, the metasilicatesmagadiite, natrosilite, kenyaite, makatite and kanemite. Other suitable starting materials include layered clays, such as bentonite, although these are swellable in water. Where the starting layered material is a layered silicate, it has been found lS to be preferable to treat the silicate wlth one or more polar solven-ts prior to or durin~ exchange with the source of organic cation. The polar solvent used should exhibit electric dipole moments in the gas phase of at least 3.û Debyes (D), prefPrably at least 3.5 Debyes, m~st preferably at least about 3.8D. Examples of ! 20 suitable solvents are water, dimethylsulfoxide (DMSO) and dimethylformamide (DMF). A table of selected organic compounds and their electric dipole moments can be found in CRC Handbook of Chemistry and Physics, 61st Edition, 198û-1981 at pages E-64 to E-660 It is believed that the treatment of the oxide s-tarting material with one or more highly polar solvents facilitates the introduction of the source of organic cation bet~een the layers of the starting material.
In one preferred embodiment, the starting material is a layered oxide of Group IV A metal such as titanium, zirconium and hafnium, with a layered titanate, e.g., a trititanate such as Na2Ti307, being particularly preferred. Trititanates are commercially available materials whose structure consists of anionic sheets of titanium octahedra with interlayer alkali metal cations.
A method for making such material may be found in U.S. Patent ~ L~3 Z

7~496?993~ It is known that the interlayer distance of Na2Ti307 may be increased by replacing interlayer sodium ions with larger octylammonium ions. See, Weiss et al., Angew. Chem/72 Jahrg. 1960/Nr/2, pp 413-hl5. However, the organic-containing trititanate is highly susceptible to heat which can remove the organic material and cause collapse of the layered structure. The present invention serves to introduce a stable polymeric oxide, preferably silica, between adjoining layers resulting in a heat-stable material which substantially retains its interlayer distance upon calcination.
In another preferred embodiment, the oxide starting mate~ial is a layered silicate, such as magadiite, either in natural or synthetic form.
As previously stated, the starting layered oxide material is treated with an organic compound capable of forming cationic species such as organophosphonium or organoammonium ion, beFore adding the polymeric oxlde source. Insertion of the organic cation between the adjoining layers serves to physically separate the layers in such a way as to make the layered oxide receptive to the interlayer addition of an electrically neutral, hydrolyzable, polymeric oxide precursor. In particular, alkylammonium cations have been found useful in the present invention. Thus C~ and larger alkylammonium, e.g., n-octylammonium, cations are readily incorporated within the interlayer species of the layered oxides, serving to prop open the layers in such a way as to allow incorporation of the polymeric oxide precursor. The extent of the interlayer spacing can be controlled by the size of the organoammonium ion employed so that use of the n-propymonium cation will achieve a d-spacing of about 10.5A, whereas to achieve a d spacing of 20A an n-octylammonium cation or a cation o~ equivalent length is required. Indeed, the si~e and shape of the organic cation can affect whether or not it can be incorporated within the layered oxide structure at all. For example, bulky cations such as tetrapropylammonium are generally undesirable for use in the present 3~
F-~12 --8--method, ~ith ammonium cations derived from n-alkyl primary amines, more preferably primary monoamines, being preferred. The organic ammonium cations separating the oxide layers may be formed in situ by reaction of the neutral amine species with interlayer hydrogen or hydronium cations of the layer oxide starting material.
Alternatively where the interlayer cations of the layered oxide starting material are alkali metal cations, the organic ammonium cation may be formed by initially combining an amine and an aqueous acid solution, such as hydrochloric acid, and then treating the layered oxide with the resulting aqueous organoammonium ion solution. In either case, the treatment is conducted in aqueous media so that water is then available to hydroly~e the electrically neutral, hydrolyzable polymeric oxide precursor subsequently introduced into the "propped" product.
The polymeric oxide pillars formed between the layers of the oxide starting material may include an oxide of zirconium or titanium or more preferably of an element selected from Group IVB of the Periodic Table (Fischer Scientific Cw~pany Cat. No. 5-702-10), other than carbon, and most preferably include polymeric silica. In addition the polymeric oxide pillars include an element which provides catalytically active acid sites in the pillars, preferably aluminum.
The polymeric oxide pillars are formed from a precursor material which is preferably introduced between the layers of the organic propped species as a cationic, or more preferably electrically neutral, hydrolyzable compound of the desired Group IV~
elements. The precursor material is preferably an organometallic compound which is a liquid under ambient conditions. Suitable polymeric silica precursor materials include tetrapropylorthosilicate, tetramethylorthosilicate and, most preferably, tetraethylorthosilicate. Where the pillars are also required to include polymeric alumina, a hydrolyzable aluminum compound is contacted with the organic propped species before, after or simultaneously with the silicon compound. Preferably, the aluminum compound is aluminum isopropoxide.

,~ "

F-3812 __9__ ~l3~2 After hydrolysis to produce the polymeric oxide pillars and calcination to remove the organic propping agent, the ~inal pillared product may contain residual exchangeable cations. For example, sodium titanate pillared with polymeric silica may contain 2-3% of weight of residual sodium. Such residual cations can be ion exchanged by methods well known with other cationic species to provide or alter the catalytic activity of the pillared product.
Suitable replacement cations include cesium, cobalt, nickel, copper, zinc, manganese9 platinum, lanthanum, aluminum and mixtures thereof.
The present invention is illustrated further by the following examples.
In these examples, adsorption data were determined as follows: A weighed sample was contacted with the desired pure adsorbate vapor at a pressure less than the vapor-liquid equilibrium pressure of the adsorbate at room temperature. Adsorption was complete when a constant pressure in the adsorption chamber was reached (overnight for water, 3 hours for hydrocarbons); e.g., 12 mm of mercury for waker and 4û mm for n-hexane and cyclohexane.
Samples were then removed and weighed. The increase in weight was calculated as the adsorption capacity of the samples. Nitrogen BET
surface areas were reported in m2Jg~ X-ray diffraction data was obtained by standard techniques using K-alpha double-t of copper radiation.
When Alpha Value is examined, it is noted that the Alpha Value is an approximate indication of the catalytic cracking activity of the catalyst compared to a standard catalyst and it gives the relative rate constant (rate of normal hexane conversion per volume of catalyst per unit time). It is based on the activity of the highly active silica alumina cracking catalyst taken as an Alpha of 1 (Rate Constant = 0.16 sec ). The Alpha Test is described in U S. Pa-tent },354,û78 and in The Journal_of Catalysis, Vol. IVc pp. 522-529 (August 1965).

Example 1 a) A gel was produced by mixing 400 g Cabosil silica in 54.4 9 98% NaOH and 1.4 kg water. The gel was crystallized in a 2 liter polypropylene jar at 100C for 23 days to produce synthetic magadiite, which was then filtered, washed with hot water and dried at (25ûF) overnight. The dried product had the following composition (wt%):

SiO2 83.3 Na20 6.9 A120~ O.ûl 100 9 of the dried product was added to 600 ml of distilled water, titrated with 0.1 N HCl to a pH of 2, and held at pH of 2 for 24 hours. The product, after being filtered, washed with 8 liters of distilled water, and air dried on the ~ilter, had 95 ppm Na.
The resultant product (80 9) was treated for 24 hours with a solution of 80 9 of octylamine in 160 9 of DMSO, filtered, air dried and then held for subsequent treatments.
b) A solution of tetraethylorthosilicate (TEOS) and aluminum isopropoxide (AIP) was prepared as follows:
80 9 o~ aluminum isopropoxide (30-35~) in isobutanol (Al~a) were placed in a 250 ml polypropylene bottle and heated in a steam chest at lû0C for 16 hours. 51.0 9 TEOS (Baker, practical grade) were added and this sol~tion was stirred for 3 days at room 2s temperature.
20 9 of the octylamine propped product of (a) above were reacted with the TEOS/AIP solut;on for 3 days in a polypropylene bottle which was tightly sealed. The slurry was filtered, air dried, and calcined for 2 hours at 510C (950F) in air. The final product had an alpha = 5 and the following composition (wt. %):

SiO2 72.90 A1203 16.8 * Trade Mark ~. ., ..1,. .

LL~32 F-3812 -~

Exame~es 2 and 3 Further 20 9 samples of the propped product of Example l(a) were reacted respectively with 100 g samples of titanium tetraisopropoxide (Example 2) and tetraethylorthosilicate (Example 3). Each reaction was conducted at room temperature for 3 days in a sealed polypropylene bottle, whereafter the resultant - slurry was filtered, air-dried and calcined for 2 hours at 538C
(lû00F) in air. The products had the following properties:

Composition (wt %) lo Example Alpha SiO Al 0 Ti

2 - 2 3 2 3 53.7 0.015 27

3 1 94 0~0025 EX~MPLE 4 a) llû 9 of the acid form of synthetic magadiite prepared in a manner analogous to Example 1 were treated with a solution of 150 g of octylamine in 300 9 of distilled water for 24 hours at room temperature. The slurry was filtered to a wetcake, reslurried (285 g of wetcake in 5.7 liters of distilled water), left for approximately 1 hour at room temperature, and refiltered. The product was composed of 238 g of paste~ e material (41.54% solids).
b) 294.2 9 of aluminum isopropoxide ~30-35%) in isobutanol were placed in a polypropylene bottle in a steam chest (lû0C) overnight~ 171.6 9 of solution was recovered after overnight heating. 220 g of tetraethylorthosilicate were added to the aluminum isopropoxide solution and the mixture was magnetically stirred for 9 days at room temperature.
c) The product (b) was added to the product (a) then an additional 400 9 of fresh tetraethylorthosilicate were added. This mixture was reacted for 65 hours at room temperature in a sealed polypropylene bottle with magnetic stirring. The slurry was filtered with difficulty, air dried, dried overnight at 110C and then calcined at 538C for 1 hour in flowing nitrogen followed by 3~

2 hours in flowing air. The final product had an alpha = 10 and the following composition (wt %):
SiO2 83.1 A1203 8.7 The surface area and sorption properties of the calcined magadiites obtained in Examples 1 - 4 are summarized in the ~ollowing table:

Sorption Capac_ty Example Surface Area m2/g H Cy-C6 n-C6 (12 Torr) (40 Torr) (40 Torr) 1 289 14.2 8.2 ~.7 2 158 9.2 4.~ 3.3 3 307 7.2 6.0 ~.3

4 450 16.3 12.3 10.9

Claims (16)

Claims:

1. A method for preparing a catalytically active layered oxide product having adjacent layers separated by pillars of a polymeric oxide which method comprises start-ing with a layered oxide material of an element ranging in atomic number from 13 to 15, 21 to 33, 39 to 51, 57 to 83 and greater that 90, said layered oxide material having anionic sites associated therewith; physically separating the layers of the oxide material by introducing an organic cationic species between the layers at said anionic sites;
introducing between the separated layers of said layered oxide at least one compound capable of conversion to a polymeric oxide and at least one compound capable of conversion to produce catalytically active sites; and converting said compounds to produce polymeric oxide pillars containing catalytically active sites separating adjacent layers of the layered oxide material.

2. The method of claim 1 wherein said organic cationic species is an alkylammonium cation having at least 3 carbon atoms.

3. The method of claim 2 wherein said alkylammonium cation is derived from an n-alkyl primary monoamine.

4. The method of claim 1 wherein said at least one compound capable of conversion to a polymeric oxide is hydrolyzable into said polymeric oxide and said conversion step comprises hydrolysis of said compound.

5. The method of claim 4 wherein said at least one compound capable of conversion to a polymeric oxide is an organic compound of silicon, germanium, tin, lead, zirconium or titanium.

6. The method of claim 1 wherein said at least one compound capable of conversion to produce catalytically active sites is converted by hydrolysis.

7. The method of claim 6 wherein said at least one compound capable of conversion to produce catalytically active sites in an organoaluminum compound.

8. The method of claim 1 wherein said at least one compounds are a tetraalkylsilicate and an aluminum alkoxide.

9. The method of claim 1 wherein the layered oxide is an oxide of silicon or titanium.

10. The method of claim 1 wherein the layered oxide is non-swellable.

11. The method of claim 1 wherein the layered oxide is a clay.

12. A layered product comprising a non-swellable layered oxide of an element ranging in atomic numbers from 13 to 15, 21 to 33, 39 to 51, 57 to 83 and greater than 90 inclusive, and pillars separating the oxide layers, the pillars containing at least one polymeric oxide and catalytically active sites.

13. A layered product comprising a layered oxide of an element ranging in atomic numbers from 13 to 15, 21 to 33, 39 to 51, 57 to 83 and greater than 90, inclusive, and pillars separating the oxide layers, the pillars con-taining a polymeric oxide of an element selected from Group IVB of the Periodic Table and catalytically active sites, said composition having a d-spacing greater than about 10A.

14. The composition of claim 12 or claim 13 wherein said layered oxide of an element selected from silicon, titanium, zirconium, and hafnium.

15. A layered silicate composition comprising pillars of a polymeric oxide of an element selected from silicon, titanium, zirconium and hafnium between the silicate layers, the pillars containing catalytically active sites.

16. The layered silicate of claim 15 wherein the pillars comprise an oxide of aluminum which provides said catalytically active sites.