Title of Invention

NOVEL MESOPOROUS CATALYSTS FOR INDUSTRIAL PROCESSES

Abstract

The present invention relates to a novel active mesoporous superacid and stable catalyst characterized by strong acidic centers of molybdenum zirconia in the framework of well-defined mesoporous materials and also to a process for synthesizing the said catalyst comprising introduction of molybdenum in the tetragonal phase of zirconium in to the pores of hexagonal mesoporous silica. The hexagonal mesoporous superacid catalyst formed is reusable, and compatible with microwave irradiation.

Full Text

FORM2 THE PATENTS ACT, 1970 (39 of 1970) & The Patents Rules, 2006 PROVISIONAL SPECIFICATION (See section 10; rule 13) 1. Title of the invention - NOVEL MESOPOROUS CATALYSTS FOR INDUSTRIAL PROCESSES 2. Applicant(s) (a) NAME : Mumbai University Institute of Chemical Technology (b) NATIONALITY: Indian. (c) ADDRESS : Mumbai University Institute of Chemical Technology, Matunga, Mumbai 400-019 3. PREAMBLE TO THE DESCRIPTION The following specification particularly describes the invention and the manner in which it is to be performed. FIELD OF INVENTION The present invention relates to a novel active mesoporous superacid and stable catalyst. The present invention in particular relates to a novel catalyst hereinafter referred as MUICaT-1 characterized by strong acidic centers of molybdenum zirconia in the framework of well-defined mesoporous materials. BACKGROUND OF INVENTION Zeolites opened up avenues for solid acids as catalysts for industrial applications. However, their microporosity was a severe limitation and ordered mesoporous materials were badly required. The invention of hexagonally ordered mesoporous silicate with large pore diameter such as FSM-16, MCM-41 and HMS paved way to new applications. These materials are catalytically inactive due to absence of active sites. Silica, alumina and zeolite have been shown to be excellent support for the preparation of many acidic and super acid catalysts but there are still many limitations as regards diffusion problems. Some metal oxides, when sulfated, develop the ability to catalyze reactions which are characteristic of very strong acid catalysts at low temperature, although with limited life time. A range of active sulfate promoted metal oxides includes Zr02, Ti02, Sn02, Fe203) Hf02 etc. A variety of sulfation reagents can be used; but most researchers have employed dilute sulfuric acid (usually 0.1 M). US Patent No. 6204424 relates to synergistic heterogeneous solid catalyst comprising a synergistic combination of sulfated metal oxide and mesoporous zeotypes comprising: Silicon (Si) 50-60 wt %, Zirconium (Zr) 40-50 wt %, Sulfur (S) 5-10 wt % and having > a surface area in the range of 200-500 m2/g; >• a pore volume in the range of 0.1-0.3 m3/g; > a pore diameter in the range of 25-35 A0; and > a XRD peak at 2 theta being 0-3. The patent further describes the catalyst activity for various solid acid catalyzed reactions like alkylation of ethyl benzene with ethanol, oligomerisation of 1-decene, 1-octene and 1- 2 dodecene, acylation of benzene with 4-chlorobenzoyl chloride, alkylation of p-cresol with methyl tert-butyl ether (MTBE), alkylation of benzene/toluene with benzyl chloride. But treatment by sulfuric acid has its own limitation for these catalysts due to its perilous properties. Sulphuric acid when used in higher than IN concentrations tend to form sulphates with entire material instead of incorporating sulphate atoms on the surface of catalyst. Thus there is a limit to increase the acidity of solid materials beyond a certain range. In majority of cases the concentration of sulfur in form of sulphates in solid superacids is 4-5% and it is necessary to maintain crystallinity of material. So incorporation of higher quantity of sulfur requires agents other than sulphuric acid. Thus constant research is being done to find the alternative to sulfuric acid, and develop novel catalysts with higher surface area and larger pore size and evaluate their activity, selectivity and reusability in industrial processes where pore size and surface area play significant role. It has been observed in recent times that superacidity on oxide of Zr, Ti and Fe gets generated by treating it with M03 oxide. However, it has a very wide pore size distribution and its surface area is around 100 m2g_1. It has been reported that MCM-41 impregnated with 6 wt. % M0O3 suffered a drastic destruction of MCM-41. Also, amorphous structures for Mo-MCM-41 with Mo loadings of about 10% w/w are obtained. Prior art also supported molybdenum and zirconia mixed oxides over MCM-41. The acidity of their catalyst was weaker than that of Y-zeolite. However there is a problem in the stability of the catalyst in the presence of corrosive acids. Y-zeolite is a micro-porous catalyst and its channels get blocked with reactants and products and catalyst gets useless after single use. Therefore, there is a need in the prior art to develop a superacid catalyst with higher surface area and test its activity and stability in the presence of corrosive acids like HC1 and in the presence of microwave irradiation. Generally, it is observed that in presence of microwave irradiation, structure of heterogeneous catalysts get modified and this affects its reusability 3 and hence, there is a need to develop reusable catalyst whose activity is not lost. The present invention involves the incorporation of M0O3 in zirconia based mesoporous superacid. This catalyst is designated as MUICaT-1. OBJECT OF THE INVENTION It is an object of the present invention to provide a hexagonal mesoporous superacid catalyst possesing strong acidic centers of molybdenum zirconia in the framework of well-defined mesoporous materials. It is another object of the present invention to provide a process for the synthesis of a hexagonal mesoporous superacid catalyst. It is yet another object of the present invention to provide a hexagonal mesoporous superacid catalyst that is reusable. It is a further object of the present invention to provide a hexagonal mesoporous superacid catalyst that is compatible with microwave irradiation. SUMMARY OF THE INVENTION According to one aspect of the present invention, there is provided a hexagonal mesoporous superacid catalyst comprising strong acidic centers of molybdenum zirconia in the framework of well-defined mesoporous materials. According to another aspect of the present invention, there is provided a hexagonal mesoporous superacid catalyst comprising strong acidic centers of molybdenum zirconia in the framework of well-defined mesoporous materials having a surface area in the range of 600 to 1000 square metres per gram. According to yet another aspect of the present invention, there is provided a hexagonal mesoporous superacid catalyst comprising strong acidic centers of molybdenum zirconia in 4 the framework of well-defined mesoporous materials having a pore size in the range of 20A° - 45A° (2.0 nm - 4.5 nm). According to another aspect of the present invention, there is provided a process for the preparation of the mesoporous superacid catalyst comprising the introduction of molybdenum in the tetragonal phase of zirconium in to the pores of hexagonal mesoporous silica. BRIEF DESRIPTION OF ACCOMPANYING FIGURES Figure 1: Infrared spectra of MUICaT-1 Figure 2: N2 adsorption isotherm A: Hexagonal mesoporous silica (HMS), B: MUICaT-1 Figure 3: XRD a) MUICaT-1, b) HMS, c) S-Zr02, d) Mo03-Zr02 Figure 4: SEM of HMS and MUICaT-1 DETAILED DESCRIPTION OF THE INVENTION Accordingly, the present invention involves the unique approach of introducing strong acidic centers of molybdenum zirconia into the framework of well-defined mesoporous materials leading to the development of a novel catalyst MUICaT-1 which has its own distinct advantages. The IR spectrum of the MUICaT-1 shows broad band at 3469.9cm"1 corresponding to the stretching vibration voH of the hydroxyl group. It would mean that during calcination at 650°C, condensation of the hydroxyl group of Zr(OH) 4 occurs inside the porous matrix of hexagonal mesoporous (HMS) leading to a crystalline zirconia without any change in the nature of the catalyst. An additional band at 1631-1642cm"1 is attributed to 80-H bending frequency of water molecules. A band is noticed at 1085.4cm"1, which is typical of stretching mode of silica, accompanied by a shoulder at nearly 1250cm"1 on the surface of the both HMS and MUICaT-1 (Fig.l).The band at 802.22 cm"1 is characteristic of Si-0 bonds forming bridges in a ring structure in silica prepared by sol-gel. A shoulder at 500 cm"1 is ascribed to the stretching frequency of Zr-O bonds. The textural characterization of HMS and MUICaT-1 was determined by N2 adsorption-desorption isotherm and Barret-Joyner-Halenda (BJH) pore size distribution (Table 1). Both 5 HMS and MUICaT-1 exhibit a type IV adsorption isotherm (Fig.2) that is typical of mesoporous materials, with well defined step in N2 adsorption curve between partial pressures, P/Po, of 0.4 to 0.8 and large hysteresis loop due to capillary condensation in the mesoporous channels and this explanation is in accordance with IUPAC classification. BJH analysis of the adsorption data, assuming cylindrical pores, shows that the MUICaT-1 has a mean pore diameter of 41 A0 showing that average pore diameter gets reduced from 41 A0 of HMS to 28A° which confirmed uniform distribution of Molybdenum Zirconia in MUICaT-1. HMS has a uniform mesoporosity and the distribution of molybdenum inside HMS leads to the new material MUICaT-1. Thus, there is a decrease in surface area and pore volume of MUICaT-1; however both these values are far greater than those of bulk unsupported molybdenum zirconia. MUICaT-1 has more number of acidic centres per unit mass of catalyst and thus the densities of active sites is more in these materials. The structural integrity of HMS and MUICaT-1 was determined with X-ray diffraction (XRD) (Fig.3). One diffraction peak in the low angle region (20 =1-10°) is visible indicating that HMS has a long-range hexagonal ordering and the structural integrity of HMS is retained in MUICaT-1, although the intensity of diffraction peak of HMS decreases slightly after precipitation of zirconium hydroxide and impregnation of M0O3. Pure zirconia transforms into monoclinic phase from tetragonal phase above the calcination temperature of 600 °C. Mo03-Zr02 gives a tetragonal phase in the ordinary region (20 =30°). However, a completely different diffraction pattern is obtained for MUICaT-1. MUICaT-1 did not show peaks in the ordinary range i.e. probably 2Q = 30° which is the traditional peak of tetragonal phase, which might be due to the very high reflection of silica that overcomes the intensity of tetragonal phase. The stabilization of tetragonal phase of the zirconia (Fig.3) by sulfate ion using sulfuric acid is well known for S-Zr02. The same phenomenon was also predictable in MUICaT-1 which would mean that there was an introduction of M0O3 through molybdic acid treatment, which stabilizes the tetragonal phase of the zirconia in to pores of the HMS. Fig. 4 shows SEM of HMS and MUICaT-1, respectively. The morphology of the catalyst is same as that of HMS. The catalyst is made up of sub-micrometer size free standing or aggregated sphere shaped particle. The EDXS analysis (Table 1) shows the incorporation of 6 zirconia and molybdenum in HMS. Molybdenum Kal and zirconium Lai distribution spectra determined by SEM-EDXS analysis have clearly shown homogeneous distribution of Mo and Zr atoms in MUICaT-1. Further EDXS analysis did not detect the presence of chloride in MUICaT-1 showing that sample is totally free from the chloride ion. SEM and EDXS analysis further supports the argument that active centres of Mo03-Zr02 are successfully embedded in HMS and structural integrity of HMS is not altered even after it is converted to MUICaT-1. Element Weight % Atomic% OK 54.49 67.76 SiK 45.54 32.24 Totals 100.00 Element Weiqht % Atomic OK 50.21 68.96 SiK 35.28 27.61 ZrL 9.21 2.22 MoL 5.30 1.21 Totals 100.00 EDXS of HMS EDXS of MUICaT-1 Table 1: EDXS of HMS and MUICaT-1 The efficacy of the MUICaT-1 was compared with UDCaT-1 alone in microwave condensation of benzaldehyde with acetophenone and in liquid phase alkylation of toluene with benzyl chloride as test reactions. Table 2 shows that for both reactions conversion of MUICaT-1 is much higher than that of UDCaT-1. This increase in the activity of the MUICaT-1 is attributed to uniform generation of highly active centers on HMS. For condensation reaction reusability was examined in microwave irradiation to observe no deactivation and structure change of catalyst. The reusability of the catalyst was tested five times in the benzylation of toluene. It was observed that MUICaT-1 shows the same activity after fifth use. 7 Table 2: Different parameter of MZ and MUICaT-1 and UDCaT-1 Parameters Catalysts HMS MZ MUICaT-1 UDCaT-1 Single Point Surface Area m2g_1 771 120 502 - BET surface Area (m2 g"1) 771 116 507 - Langmuir Surface Area m2g-' 1038 153 708 - BJH Adsorption Cumulative Surface Area m2g-' 528 25 250 BJH Desorption Cumulative Surface Area m2g-' 615 35 190 Single Point Total Pore Volume cmV 0.796 0.081 0.364 BJH Adsorption Cumulative Pore Volume cm3g"' 0.707 0.040 0.263 BJH Desorption Cumulative Pore Volume cm3g_1 0.880 0.074 0.33 Average Pore Diameter (4V/A by BET) A0 41 28 28 ™ BJH Adsorption Average Diameter (4V/A) A0 53 64 42 BJH Desorption Average Diameter(4V/A) A0 57 83 70 Conversion of benzyl chloride (%)a - - 100 45 Conversion of benzaldehyde (%)b - - 100 70 a) Alkylation of toluene with benzyl chloride: Mole ratio: Toluene: Benzyl chloride: 10: 1, Speed of agitation: lOOOrpm, Temperature: 90 °C, Catalyst loading: 0.05 g/cm3, Reaction time: lhr. 8 EXAMPLES Example 1: Preparation of Mesoporous Superacid Catalyst Preparation of ordered Hexagonal Mesoporous Silica (abbreviated as HMS) was prepared as per prior art (G. D. Yadav, M. S. Krishnan, A. A. Pujari, N. S. Doshi, M. S. M. Mujeebur Rahuman, US Patent 6, 204, 424 Bl, 2001). Molybdenum zirconia on HMS designated as MUICaT-1 was prepared by dissolving the desired quantities of zirconium oxy chloride in aqueous solution and added to precalcined HMS by incipient wetness technique. After addition the solid was dried in an oven at 120°C for 3 hours. The dried material was then hydrolyzed by ammonia gas and washed with distilled water until no chlorine ion was detected and then dried in oven for 2 hours at 120°C. The generation of super acidic centres in this material was made possible by addition of molybdic acid in the above material followed by hydrothermal treatment and then calcined at 650 °C for 3 hours. Infrared spectra of the samples pressed in KBr pellets were obtained at a resolution of 2cm"1 between 4000 and 350cm'1. Spectra were collected with a Shimadzu instrument and in the each case the sample was referenced against a blank KBr pellet. Surface area measurements and pore size distributions analysis were done by nitrogen adsorption on Micromeritics ASAP 2010 instrument at an adsorption temperature 300° C, after pretreating the sample under high vacuum at 300°C for 4 h. Powder X-ray diffraction patterns were obtained using Cu Ka radiation (k= 1.540562). Samples were step scanned from 1 to 40 in 0.045 steps with a stepping time of 0.5 s. The elemental compositions of HMS and MUICaT-1 were obtained by Energy Dispersive X-ray Spectroscopy (EDXS) on KEVEX X-ray spectrometer. Scanning electron micrographs of HMS and MUICaT-1 were taken on Cameca SU 30 microscope. The dried samples were mounted on specimen studs and sputter coated with a thin film of gold to prevent charging. The gold coated surface was then scanned at various magnifications on the SEM. 9 Example 2: Alkylation of toluene with benzyl chloride Liquid phase reactions of toluene and benzyl chloride were conducted in a glass reactor of 5 cm. i.d. and 10 cm height with four glass baffles and four bladed disc turbine impeller located at a height of 0.5 cm from the bottom of the vessel and mechanically agitated with an electric motor. The reaction mixture was allowed to reach the desired temperature, the initial/zero time sample collected and catalyst added thereafter. Samples were withdrawn periodically and analyzed by a Chemito GC equipped with a stainless steel column (dia.1/8" and length 4m) packed with liquid stationary phase of 10% OV-17 on Chromosorb WHP, and a FID detector. Synthetic mixtures were used to calibrate and quantify the data. The experimental set-up for the microwave experiment was the commercially available "Discover" unit (CEM-SP1245 model Corp. USA). It consists of a circular single-mode cavity design which directs the microwave energy into a defined area, resulting in a homogenous field pattern surrounding the sample. "Focusing" the microwave energy in this manner enables the system to provide reproducible reaction conditions. It incorporates temperature and pressure feedback systems for complete control on the reaction conditions. It incorporates temperature and pressure feedback systems for complete control on the reaction conditions. The reactor consisted of 3.5 cm i.d. fully baffled mechanically agitated reactor of 150 cm3 capacity, which was equipped with four fixed baffles and a six-bladed pitched-turbine impeller. The reaction was allowed to reach the desired temperature (130 °C) and the initial/zero time sample was collected. The catalyst was added when the desired temperature was attained. All the reactions were carried out at 130 °C and 1000 rpm. It is important to note here that the power supplied to the system, during the entire reaction duration, was below 50 watts. This was done to study the rate enhancement effect with reasonable power inputs unlike the earlier reports where very high power (100-600 watts) was used. Example 3: Condensation of benzaldehyde with acetophenone Benzaldehyde (0.03 mol) and acetophenone (0.15 mol) were taken with a catalyst loading of 0.05 g/cm3. Samples were withdrawn periodically and analyzed by gas chromatograph equipped with a stainless steel column (1/8 inch, 4m) packed with 10 % OV-17 on Chemosorb W. Identification of products was done by GC-MS analysis. 10 WE CLAIM: 1. A mesoporous superacid catalyst comprising strong acidic centers of Molybdenum zirconia in the framework of well-defined mesoporous materials. 2. The hexagonal mesoporous superacid catalyst as claimed in claim 1 having a homogeneous distribution of Molybdenum and Zirconia atoms. 3. The hexagonal mesoporous superacid catalyst as claimed in claim 1 having an uniform mesoporosity of both hexagonal mesoporous silica (HMS) 4. The hexagonal mesoporous superacid catalyst as claimed in claim 1 wherein the framework of well-defined mesoporous materials has a surface area in the range of 600 to 1000 square metres per gram. 5. The hexagonal mesoporous superacid catalyst as claimed in claim 4 wherein the framework of well-defined mesoporous materials has surface area of 800 square metres per gram. 6. The hexagonal mesoporous superacid catalyst as claimed in claim 1 wherein the framework of well-defined mesoporous materials has a pore size in the range of 30A° -35A° 7. The hexagonal mesoporous superacid catalyst as claimed in claim 6 wherein the framework of well-defined mesoporous materials has a pore size of 28A°. 8. The hexagonal mesoporous superacid catalyst as claimed in claim 1 wherein the framework of well-defined mesoporous materials has a pore size in the range 3.0 nm - 3.5 nm. 11 9. A process for the preparation of the mesoporous superacid catalyst comprising the introduction of molybdenum in the tetragonal phase of zirconium in to the pores of Hexagonal Mesoporous Silica. 10. The process for the preparation of the mesoporous superacid catalyst comprises the step of: a) dissolving zirconium oxychloride in aqueous solution, b) addition of the above solution to precalcined Hexagonal Mesoporous Silica (HMS) c) drying of the solid in an oven d) hydrolyzing with ammonia 11. The hexagonal mesoporous superacid catalyst as claimed in claim 1 in the reaction of alkylation of toulene with benzoyl chloride. 12. The hexagonal mesoporous superacid catalyst as claimed in claim 1 in the reaction of condensation of benzaldehyde with acetophenone Dated this 18th day of May 2007 (\jjf^^ Ashwini Sandu OfS. Majumdar&Co. 12 ABSTRACT TITLE: NOVEL MESOPOROUS CATALYSTS FOR INDUSTRIAL PROCESSES The present invention relates to a novel active mesoporous superacid and stable catalyst characterized by strong acidic centers of molybdenum zirconia in the framework of well-defined mesoporous materials and also to a process for synthesizing the said catalyst comprising introduction of molybdenum in the tetragonal phase of zirconium in to the pores of hexagonal mesoporous silica. The hexagonal mesoporous superacid catalyst formed is reusable, and compatible with microwave irradiation. 13

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