DESC:AN IMPROVED PROCESS FOR THE ACID-MEDIATED SYNTHESIS OF ORDERED MESOPOROUS ALUMINOSILICATES AND THE PRODUCT THEREOF
TECHNICAL FIELD
[0001]Embodiments are generally related to the field of chemistry. Embodiments are specifically related to aluminosilicates. Embodiments are further related to the process of synthesis of ordered mesoporous aluminosilicates. Embodiments are particularly related to developing an ordered mesoporous aluminosilicate.
Background of the Invention
[0002]Ordered mesoporous aluminosilicates are of much interest to chemical industries due to their potential in applications as support structure for carrying catalysts, separation, selective adsorption and their ability to confine molecules in their pores. Some of these applications are accomplished by ordered mesoporous silicates due to their high surface area and large pore sizes. Since the discovery of MCM-41, a key scientific objective has been the synthesis of mesoporous materials with higher content of tetrahedral aluminium in the mesoporous framework because the tetrahedrally coordinated trivalent aluminum atoms are considered to be the major interaction sites for guest molecules and the origin of acidity
[0003]Ordered mesoporous aluminosilicates (OMAS) of the type H-AlSBA-15 synthesized in acid medium with medium-to-strong Brønsted acidity have great potential as heterogeneous solid acid catalysts owing to high thermal and hydrothermal stability in conjunction with large pores with in-built microporosity. However, the synthesis of H-AlSBA-15 with trivalent aluminium in tetrahedral framework is highly difficult owing to: (i) existence of trivalent aluminium as hexaaqua ions under acidic conditions; (ii) differences in the hydrolysis rates of both silicon and aluminium sources employed for the preparation, and (iii) easy dissociation of the formed AlOSi bonds.
[0004]Although several synthesis methods are available for the preparation of H-AlSBA-15, they all show part of aluminium present in penta- and/or hexa-coordination. Further, none of these methods yield materials with trivalent aluminium exclusively in tetrahedral framework structure without affecting their textural properties (i.e., pore size distribution and wall thickness), and hence it is real challenge to the scientific community.
[0005]Therefore the current invention fills this gap in the prior art, where we have developed a new method, referred as intrinsic hydrolysis method, in which the hydrolysis rates of both the aluminium and silicon sources are matched in such a way that the condensation occurs simultaneously.

summary of the Invention
[0006]The following summary is provided to facilitate an understanding of some of the innovative features unique to the disclosed embodiment and is not intended to be a full description. A full appreciation of the various aspects of the embodiments disclosed herein can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
[0007]One aspect of the disclosed embodiments is to provide an improved method for efficient synthesis for the preparation of acid mediated ordered mesoporous aluminosilicates without disturbing the mesostructure even at high aluminium content.
[0008]Another aspect of the disclosed embodiments to is to provide an improved ordered mesoporous aluminosilicate with excellent structural and textural properties.

[0009]Yet another aspect of the disclosed embodiments is to provide an improved acidic generated OMAS give excellent catalytic activity towards t-butylation of phenol with selective formation of 4-t-BP and 2,4-di-t-BP

[0010]The aforementioned aspects and other objectives and advantages can now be achieved as described herein. 2.8 g of aluminium nitrate nonahydrate and 3.1 g of citric acid monohydrate were dissolved in 140 mL of water. This mixture was stirred overnight at 40-50°C. Water was removed from the mixture by using rotary evaporator. The viscous material obtained was dissolved in less volume of water and pH was adjusted to 8 using dil. NH3, to which absolute ethanol was added at 4°C in order to obtain crystalline aluminium citrate. A 4.0 g of Pluronic P-123/Brij-56 was added to 30 mL of water and stirred till a clear solution was obtained. Thereafter, 70 mL of 0.086 M HCl was added, stirred for 2 h and pH was adjusted to 1.5. Then, 0.04 mol of tetraethyl orthosilicate (log K = 11.8) and aluminium citrate (log K = 11.7) were added at 2 h interval, so that the mixture will have Si/Al ratio of 30/60/90 in the gel and the resultant mixture was stirred at 40°C for 22 h. The mixture was transferred to an autoclave and then kept for hydrothermal treatment at 100°C for 24 h. Obtained precipitate was filtered, washed, dried at 60°C for 6 h and was calcined at 550°C for 1 h in nitrogen and 5 h in air atmosphere at a heating rate of 1°C min. The resultant surfactant free samples are designated as H-AlSBA-15/H-AlIITM-56.
[0011]This invention presents a unique approach, viz., intrinsic hydrolysis method, that relies mainly on hydrolysis rates/stability constant (log K) of inorganic (silicon and aluminium) precursors used for the preparation in such a way that the condensation occurs simultaneously, and therefore overcomes the usually encountered difficulties in stabilizing isomorphous substitution of aluminium ions in the tetrahedral silicate matrix even at high aluminium content. In this way, we could successfully synthesize high quality Brønsted acidic novel ordered mesoporous aluminosilicates, viz., H-AlSBA-15 and H-AlIITM-56, with trivalent aluminium in tetrahedral coordination in the silicate matrix having medium-to-strong Brønsted acid sites, hitherto, not reported so far. Furthermore, as expected, these acid catalysts exhibit excellent activity towards tertiary-butylation of phenol with a combined high selectivity of para-tertiary-butylphenol (4-t-BP) and 2,4-di-t-butylphenol (2,4-di-t-BP).
[0012]All the materials under study were systematically characterized by various analytical, spectroscopic and imaging techniques, viz., XRD, TEM, SEM, 29Si MAS-NMR and 27Al MAS-NMR, XRF and NH3-TPD.
[0013]The process proposed herein is an exemplary demonstration of working of the proposed concept of an improved process for acid mediated synthesis of ordered mesoporous aluminosilicates and the product thereof. The standards and operating protocol for acid mediated synthesis of OMAS of the use of the resultant product thereof can be standardized and adapted by a person skilled in the art to achieve the same or enhanced results.

Brief description of drawings

[0014]The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention.
[0015]FIG. 1 illustrates X-Ray Diffraction (XRD) patterns (A) and N2 sorption isotherms with pore size distribution (B) of: (a) H-AlSBA-15(30); (b) H-AlIITM-56(30), in accordance with the disclosed embodiments.
[0016]FIG. 2 illustrates Transmission Electron Microscopy (TEM) images of: (a) H-AlSBA-15(30); (b) H-AlIITM-56(30), in accordance with the disclosed embodiments.
[0017]FIG. 3 illustrates Scanning Electron Microscopy (TEM) images of: (a) SBA-15; (b) H-AlSBA-15(30); (c) IITM-56; (d) H-AlIITM-56(30), in accordance with the disclosed embodiments.

[0018]FIG. 4 illustrates 27Al MAS-NMR spectra of: a) H-AlSBA-15(30); (b) H-AlIITM-56(30), in accordance with the disclosed embodiments.

detailed description
[0019]The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.
[0020]The embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. The embodiments disclosed herein can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
[0021]The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
[0022]Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0023]The best mode of achieving the process of acid mediated synthesis of OMAS also referred to as intrinsic hydrolysis method is as disclose herein. 2.8 g of aluminium nitrate nonahydrate and 3.1 g of citric acid monohydrate were dissolved in 140 mL of water. This mixture was stirred overnight at 40-50°C. Water was removed from the mixture by using rotary evaporator. The viscous material obtained was dissolved in less volume of water and pH was adjusted to 8.0 using dil. NH3, to which absolute ethanol was added at 4°C in order to obtain crystalline aluminium citrate. A 4.0 g of Pluronic P-123/Brij-56 was added to 30 mL of water and stirred till a clear solution was obtained. Thereafter, 70 mL of 0.086 M HCl was added, stirred for 2 h and pH was adjusted to 1.5. Then, 0.04 mol of tetraethyl orthosilicate (log K = 11.8) and aluminium citrate (log K = 11.7) were added at 2 h interval, so that the mixture will have Si/Al ratio of 30/60/90 in the gel and the resultant mixture was stirred at 40°C for 22 h. The mixture was transferred to an autoclave and then kept for hydrothermal treatment at 100°C for 24 h. Obtained precipitate was filtered, washed, dried at 60°C for 6 h and was calcined at 550°C for 1 h in nitrogen and 5 h in air atmosphere at a heating rate of 1°C min1. The resultant surfactant free samples are designated as H-AlSBA-15/H-AlIITM-56.
[0024]The process for the acid mediated synthesis of OMAS also referred to as intrinsic hydrolysis method can also be achieved as disclosed herein. 1.55.0 g Aluminium nitrate nonahydrate and 1.0–7.0 g citric acid monohydrate were dissolved in approximately 150 mL of water. This mixture was stirred overnight at 30-70°C. Water was removed from the mixture evaporation. The viscous material obtained was dissolved in less volume of water and pH was adjusted to 7.09.0 using dil. NH3, to which absolute ethanol was added at 4°C in order to obtain crystalline aluminium citrate. 2.06.0 g of Pluronic P123/Brij 56 was added to approximately 30 mL of water and stirred till a clear solution was obtained. Thereafter, approximately 70 mL of 0.08 M HCl was added, stirred for 1-4 h and pH was adjusted to 1.04.0. Approximately 0.04 mol of tetraethyl orthosilicate (log K = 11.8) and aluminium citrate (log K = 11.7) were added at 1-2 h interval, so that the mixture will have Si/Al ratio of 30/60/90 in the gel and the resultant mixture was stirred at 30-50°C for 18-25 h. The mixture was transferred to an autoclave and then kept for hydrothermal treatment at about 100°C for 20-30 h. Obtained precipitate was filtered, washed, dried at 40-70°C for 4-8 h and was calcined at 500-700°C for 0.5–2 h in nitrogen and 2.0–6.0 h in air atmosphere at a heating rate of 0.52.0°C min1. The resultant surfactant free samples are designated as H-AlSBA-15/H-AlIITM-56.
[0025]The other embodiment of the invention, the OMAS synthesized by the disclosed method has large pores with inbuilt microporosity. The disclosed method of synthesis, also referred to as the intrinsic hydrolysis method, yields materials with trivalent aluminium exclusively in the tetrahedral framework structure. The novelty of the invention resides in this quality of pure phase trivalent aluminium exclusivity in the tetrahedral network. The OMAS discussed here is synthesized in acid medium with medium-to-strong Brønsted acidity have great potential as heterogeneous solid acid catalysts owing to high thermal and hydrothermal stability in conjunction with large pores with in-built microporosity. The material under study was systematically characterized by various analytical, spectroscopic and imaging techniques, viz., XRD, TEM, SEM, 29Si MAS-NMR and 27Al MAS-NMR, XRF and NH3-TPD.
[0026]In this novel intrinsic hydrolysis method the hydrolysis rates of both the aluminium and silicon sources are matched in such a way that the condensation occurs simultaneously, due to which we could successfully achieve the desired high quality H-A1SBA-15/H-AlIITM-56 even at high aluminium content, hitherto not reported so far. It is clear from these studies that the materials show well ordered, narrow-pore sized, tetrahedrally cordinated trivalent aluminium in the matrix with increased medium-to-strong Brønsted acid sites.
[0027]In this way, we could successfully synthesize high quality Brønsted acidic novel ordered mesoporous aluminosilicates, viz., H-AlSBA-15 and H-AlIITM-56, with trivalent aluminium in tetrahedral coordination in the silicate matrix having medium-to-strong Brønsted acid sites, hitherto, not reported so far.
[0028]A further aspect of the invention is the excellent catalytic activity exhibited by the disclosed product. H-AlSBA-15 and H-AlIITM-56 exhibit excellent catalytic activities towards tertiary-butylation of phenol with high selectivity towards para-tertiary butyl phenol (4-t-BP) and 2,4-di-tertiary butyl phenol (2,4-di-t-BP). Table 1 shows the table showing the acidity data and tertiary-butylation of phenol over ordered mesoporous aluminosilicates.

Material nSi/nAlb nSi/nAl?c hw
(nm) Acidic sites
(mmol g1) / TDes (°C) Phenol
Conv.
(%) Selectivity (%)
gel product Total (iii) (iv) 2-t-BP 4-t-BP 2,4-di-
t-BP
H-AlSBA-15 30 85 85 5.30 0.24 0.10/327 0.04/394 55.5 8.4 76.5 15.1
H-AlIITM-56 30 80 80 2.66 0.22 0.09/297 0.02/365 43.4 8.7 73.5 17.8
H-AlMCM-41 90 93 93 1.60 0.17 0.06/276 0.02/356 26.4 12.9 72.5 14.5
a Reaction conditions: Catalyst = 500 mg; nt-BA:npheno1= 2:1; 160°C; WHSV = 7.0 h1; TOS = 2 h.
b nSi/nAl determined by XRF; c nSi/nAl? determined by 27Al MAS-NMR.

[0029]The disclosed invention has the following improvements over the closest prior art, as describes herein. Unlike many other preparation methods, the use of intrinsic hydrolysis method isomorphously (tetrahedrally) substitutes trivalent aluminium in the silicate framework structure and produces materials with excellent structural and textural properties. The wall thickness of OMAS increases with increase of aluminium content that imparts very good hydrothermal and thermal stability. The use of aluminium citrate and tetraethyl orthosilicate, both has similar hydrolysis rate/stability constant as well as forms monomeric species, results in the formation of high quality OMAS with trivalent aluminium exclusively in the tetrahedral silicate matrix. The resulting materials, viz., H-AlSBA-15 and H-AlIITM-56, possess medium-to-strong Brønsted acid sites. The acidic generated OMAS give excellent catalytic activity towards tertiary-butylation of phenol with selective formation of 4-t-BP and 2,4-di-t-BP. Thus the intrinsic hydrolysis method is adaptable for acid-mediated synthesis of ordered porous materials.
[0030]The process proposed herein is an exemplary demonstration of working of the proposed concept of a process for the acid mediated synthesis of ordered mesoporous aluminosilicates, the product thereof and the utility of the product as a catalyst exhibiting excellent catalytic activity towards tertiary-butylation of phenol with selective formation of 4-t-BP and 2,4-di-t-BP. The standards and operating protocol for the synthesis of OMAS and the use of such product as catalyst can be standardized and adapted by a person skilled in the art to achieve the same or enhanced results.
[0031]It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the field. ,CLAIMS:I/We claim
1.     A process foracid mediated synthesis of ordered mesoporous aluminosilicates, steps comprising;
2.5-3.0g of aluminium nitrate and 3.0-3.5 g of citric acid monohydrate is dissolved in 140-150 mL water,
stirring the mixture continuously for 15-20 hours at 40-50°C,
removing water from the mixture by evaporation,
resulting viscous mixture is dissolved in 1-5ml water,
adjusting the pH to 8.0 using dilute ammonia, and
adding absolute ethanol to the above content at 4°C, to obtain crystalline aluminium citrate.
2.     The method as claimed in claim 1 further comprising steps of ,
3.5-4.5 g of Pluronic P-123/Brij-56 is added to 25-35 mL of water and stirred till a clear solution is obtained,
70mL of 0.086M HClis added and stirred for 100-140minutes and pH is adjusted to 1.5,
 0.04 mol of tetraethyl orthosilicate (log K = 11.8) and aluminium citrate (log K = 11.7) were added at 2 h interval,
resultant mixture is stirred at 40°C for 22 h and  transferred to an autoclave, and
kept for hydrothermal treatment at 100°C for 24 h to obtain a precipitate that is further filtered, washed, dried at 60°C for 6 h and was calcined at 550°C for 1 h in nitrogen and 5 h in air atmosphere at a heating rate of 1°C min-1, to obtain ordered mesoporous alumina silicate.
3.     The ordered mesoporous alumina silicate as claimed in claim 2, wherein; the aluminosilicate has trivalent aluminium exclusively in the tetrahedral framework structure.
4.     The ordered mesoporous alumina silicate as claimed in claim 2, wherein; the aluminosilicate catalyses tertiary-butylation of phenol with high selectivity towards para-tertiary butyl phenol (4-t-BP) and 2,4-di-tertiary butyl phenol (2,4-di-t-BP).