Site specific supramolecular heterogeneous catalysis by optically patterned soft oxometalate–porous organic framework (SOM–POF) hybrid on a chip

We have designed a supramolecularly bound multi-component catalytic material based on a soft oxometalate (SOM) and a porous organic framework (POF) material, which shows high catalytic conversion efficiency. We have also used this material for site directed supramolecular heterogeneous catalysis with a yield even higher than in the bulk, and with micron-level precision by controllably depositing the material on a glass substrate, making a reactor chip, using a thermo-optical tweezers. Various SOM–POF composites have been prepared in dispersion phase and patterned using thermo-optic tweezers and their catalytic activities have been compared with a benchmark molecular catalyst [PMo12]. This work can lead to further explorations for hybrid materials that are formed out of well-defined molecular level precursors which can be controllably micro-patterned to simultaneously catalyze targeted reactions.


Introduction
An immediate challenge in supramolecular catalysis is to design high surface area supramolecularly bound multi-component 20 catalytic materials in a controlled fashion. In such a design it is desired that distinct multifunctional components are held together by supramolecular interactions and they function catalytically in synergy to emulate enzymes. 1 Moreover for efficient catalysis high surface area materials are required. Hence the need of the hour for supramolecular catalysis 1 45 translates to the following questions. Is it possible to bring multiple functional components together? Can they be held together such that they can act in synergy? Can these components be patterned as ultrahigh surface area materials that show catalytic activities? Here in this paper we address these 50 challenges simultaneously. We start with a soft oxometalate, (SOM) dispersion 2 of molybdenum containing nanotubes to which we add porous organic framework (POF) material, to get a stable soft oxometalate-porous organic framework, (SOM-POF) dispersion. We then expose this dispersion to a thermo-optic laser 55 tweezers to induce a phase transition from a dispersion to a crystalline state -thereby simultaneously patterning [3][4][5][6][7][8][9][10][11] the material in solid state by translating the laser beam. 12 We further use this patterned material to carry out site-directed supramolecular catalysis. 13,14 It is perhaps now apt to introduce 60 the components of this material and the physical techniques we use separately and briefly. Soft oxometalates or SOMs are oxometalates endowed with soft matter properties 2 of transition metal-oxide clusters known as polyoxometalates (POMs). 15,16 POMs have been extensively ammonium heptamolybdate tetrahydrate as the crystalline precursor to soft oxomolybdate. The second component used in our work is POF or porous organic framework. POFs are porous materials 32 with high surface area per unit mass as compared to metal-organic 5 frameworks 33 and are extremely stable chemically as well as thermally. These materials provide accessible space within their pores for reactant molecules to react. [34][35][36][37][38][39][40] Such porous frameworks are hence known for their applications in gas storage 41-46 and separation 47 . These porous frameworks are 10 known to have affinity towards greenhouse gases such as carbon dioxide, methane, and exhibit high selectivity towards them in gas sorption studies. 48a While SOMs provide catalytic potential, POFs provide high surface area and accessible space within the framework when these two components are combined together. 15 JUC-Z4 used in this work is an electroactive porous organic framework synthesized from tris(4-chlorophenyl)phosphine, in which the radical redox centre of phosphorous is stabilized by an aromatic organic framework. The pore size, BET surface area and polarity of these organic frameworks can be manipulated and 20 controlled by redox reactions. 48a Furthermore we also synthesized composites using other POF materials such as PAF1, JUC-Z2 and JUC-Z5 to form SOM-PAF1, SOM-JUC-Z2, SOM-JUC-Z5 composites respectively. PAF1 is an extensively studied POF with exceptionally high surface area and thermal stability. It has a 25 diamondoid structure with a tetrahedral carbon surrounded by phenyl rings. JUC-Z2 is similar to JUC-Z4 except for the hetero atom in this porous material is nitrogen instead of phosphorous. JUC-Z5 on the other hand is the oxidised form of JUC-Z4 with phosphorous in the +5 oxidation state. 48 30 It is the redox activity of JUC-Z4 coupled with the presence of phosphorous in it that prompted us to ask the following questions. Phosphomolybdates are known to be catalysts for several reactions. 18,49 Can a supramolecular composite in dispersion state comprising of both molybdenum and phosphorous show 35 comparable catalytic property as that of [PMo 12 ] Keggin? Can the catalytic activity of such a SOM-POF composite (SOM-JUC-Z4) be compared with other SOM-POF composites? Can we furthermore design high surface area patterned surfaces starting from such SOM-POF supramolecular composite dispersion? In 40 addition to addressing these questions we further compare and contrast the catalytic activity of SOM-POF composites in dispersions. We demonstrate the catalytic activity of various thermo-optically patterned composite SOM-POF catalyst chips. We show the stability of such catalytic chips before and after 45 reaction and over days. We ask: can both aliphatic and aromatic aldehydes be oxidized by our method? Can other oxidants be used? How efficient is our SOM-POF chip compared to that of [PMo 12 ] benchmark catalyst? 50

Materials and Methods
Ammonium heptamolybdate tetrahydrate is used as obtained. JUC-Z4 is prepared following the previously published procedure. 48 Benzaldehyde, hydrogen peroxide and DMSO were 55 used as obtained. All chemicals are obtained from Merck. 60 1.236 g (0.001 moles) of ammonium heptamolybdate tetrahydrate is dissolved in 10 mL of distilled water to prepare 0.1 M solution. Then 0.2 M solution is prepared by dissolving 2.472 g (0.002 moles) of the heptamolybdate in 10 mL of distilled water. The two solutions of 0.1 M and 0.2 M are then warmed 65 until dispersions are obtained that scatter laser light. These SOM dispersions were refrigerated for about 10 minutes for further experiments. 70 Mole ratios of SOM and JUC-Z4 dispersions are varied from 1.3:1 to 51.8:1 (SOM:JUC-Z4) and 10 colloidal dispersions of SOM-POF hybrids are prepared. The same procedure is followed to prepare dispersions of SOM-PAF1, SOM-JUC-Z2 and SOM-75 JUC-Z5.

Description of Optical Tweezers set up
The optical patterning is done exactly similar to the procedure 80 adopted in our previous work. 12 The SOM-POF dispersion is patterned by exposing it to thermo-optical tweezers. The dispersion is placed between a 1 mm thick standard glass slide (top surface) and a 160 µm thick glass cover-slip (bottom surface). The spacing between the two surfaces is controlled by 85 putting double-sided sticky tape on the sides of the cover-slip. This set-up of slide and cover-slip stuck together with doublesided sticky tape constitute the sample holder. The dispersion in this holder is impinged with a CW laser beam which is focused to a diffraction limited spot by a high numerical aperture objective 90 lens. The thermo-optical tweezers set up is built around an inverted microscope (Zeiss Axiovert. A1Observer), and it has a 100X, 1.4 N.A. oil immersion microscope objective (Zeiss planoapochromat, infinity corrected) which is used to focus light from a diode laser (Lasever LSR1064ML) of 1064 nm 95 wavelength on the sample holder to attain a spot size of waist radius ~500 nm. The power of the laser can be varied from 0 to 100 mW after the objective. Before every experimental run, the slide and coverslip constituting the sample holder are rinsed with methanol and dried in order to remove the presence of any 100 adsorbed impurity. The sample holder containing about 75 µL of the dispersion is translated using the microscope scanning stage which is stepper motor controlled with a Ludl MAC5000 XY stage controller operated by a joystick. The total travel range of the stage is 130 x 100 mm with a resolution of 100 nm. The 105 patterning process is observed on a monitor with the help of a CCD camera (Axiovision) running at a fastest rate of 30 frames per second. A combination of 10X/40X/100X objectives and external optics are arranged outside the microscope to aid in imaging which is done at the back focal part of microscope.

FTIR Spectroscopy
Perkin Elmer Spectrum RX1 spectrophotometer is used to record the FTIR spectra in the range of 400-4000 cm -1 . 5 Low pressure N 2 adsorption measurements N 2 sorption isotherm measurements were performed with a Micromeritics Tristar II 3020 surface area and pore size analyser. Before the measurement, the sample was subjected to a degas 10 vacuum system under ultra high vacuum (90mtorr) at 100°C for 12 h. The sample was backfilled with nitrogen and transferred to the analysis system. A sample of 50mg and ultra high purity grade nitrogen (99.999%) gas source were used in the nitrogen sorption measurements at 77 K, maintained with liquid nitrogen 15 throughout the measurement. Helium was used for the free space determination after sorption analysis, both at ambient temperature and at 77K. Apparent surface areas were calculated from nitrogen adsorption data by multi-point Brunauer-Emmett-Teller (BET) analysis. Apparent micropore distributions were calculated from 20 carbon dioxide adsorption data by the density functional theory (DFT) method.

Thermogravimetric Analysis
The TGA was performed using a Shimadzu DTG-60 thermal 25 analyser system at a heating rate of 10°C min −1 to 800°C in a dried air atmosphere and the air flow rate was 30ml min −1 . The sample was loaded in an alumina pan.

30
A LABRAM HR800 Raman spectrometer is employed using the 633 nm line of a He-Ne ion laser as the excitation source to analyze the sample. 35

Transmission Electron Microscopy
The characterization of the composite was primarily done by the use of a Tecnai 20 transmission electron microscope (FEI Company) operated at an accelerating voltage of 200 kV. The 40 TEM micrographs have been processed using SIS software (Soft Imaging System). 45 Time dependent 1 H NMR measurements were performed using 400 MHz Bruker Ultrashield Plus System. We first analyze the formation of the supramolecular composite between molybdenum containing soft oxometalate and the phosphorous containing porous organic framework. To do so, we 55 first need to check whether a stable dispersion can be obtained using soft oxometalates and porous organic frameworks in synergy. We now check systematically what happens when a SOM dispersion is mixed with a phosphorous containing POF (JUC-Z4). Upon mixing, we get a colloidal dispersion of SOM- 60 POF composite. The colloidal nature of such stable dispersions is confirmed by passing laser light through these dispersions and checking for the scattering of light. We further see that as we vary the relative loading of JUC-Z4 to heptamolybdate, the system changes from unstable to a stable colloidal regime [ Fig.   65 1 (b)]. We observe that dispersions of 3.86 x 10 -5 , 7.72 x 10 -5 and 1.15 x 10 -4 moles of JUC-Z4 give stable dispersions when mixed with 0.1 M and 0.2 M ammonium heptamolybdate based SOMs in 2:1 ratio of volume. The stable dispersion is negatively charge stabilized [ Fig. 1 (b)]. 70 Now we take the stable dispersion for further characterization and catalytic studies. We first look at the FTIR spectra of the dried SOM-POF dispersion closely and compare it with the peaks of its individual components [ Fig. 1(c)]. The fingerprint peaks of ammonium heptamolybdate are retained almost unchanged in the 75 SOM-POF composite. The peak at 1400 cm -1 intensifies in the composite as compared to that of ammonium heptamolybdate. This peak is attributed to the bending mode (δ N-H ) of N-H vibration. This intensification is due to the condensation of NH 4 + counterions around the composite. We also observe shifts in the 80 peaks of JUC-Z4 in the composite. For instance, we observe a shift in the bending mode (δ C-H ) and stretching mode (ν C-H ) of C-H vibration at 845 cm -1 and 806 cm -1 , respectively in the composite. This indicates that the aromatic C-H bonds of the benzene rings of POF are getting stiffened due to the restriction 85 brought about by the surrounding heptamolybdate clusters. We also observe a slight blue shift in the band around 1123 cm -1 . This is attributed to the stretching mode (ν C-P ) of C-P vibration in the SOM-POF composite and occurs due to electron donation from heptamolybdate to positive centre of phosphorous of JUC-Z4 90 which in turn strengthens the C-P bond. materials with slight shifts in the peak values indicating successful formation of SOM-POF composites (See SI for details). The loading of PAF-1, JUC-Z2 and JUC-Z5 is varied accordingly and the variation of the zeta potential is studied for obtaining a correspondingly stable SOM-POF composite. (See SI   5 for details). We now check the Raman spectroscopic signature of the SOM-JUC-Z4 composite and compare it with the dispersion of soft oxometalates. In the Raman spectrum of the composite, there is a shift of the Mo=O peak towards higher wavenumber (~26 cm -1 ) 10 [ Fig. 2(a)]. This implies successful formation of the SOM-JUC-Z4 composite. This is so because in the composite, the polarizability of the Mo=O bond is much less since it is attached to the electron deficient JUC-Z4, as compared to SOM alone. The TGA measurements show the decomposition patterns of 15 SOM-POF material as compared to that of the starting materials viz., ammonium heptamolybdate and JUC-Z4 [ Fig. 2(c)]. It is observed that the thermal stability of the SOM-POF hybrid is enhanced to 750°C from that of 475°C of JUC-Z4 alone. The same trend is observed for SOM-PAF1, SOM-JUC-Z2 and SOM-20 JUC-Z5 where the decomposition temperature of each of the composites is increased by 200-300 °C than their POF counterparts (See SI for details). We now test further the capacity of SOM-POF composites for gas adsorption from the BET and Langmuir surface area values and also to see the pore size 25 distribution profile and compare the values with those of the precursor POFs. In order to perform sorption measurements, we make sure that there are no guest molecules such as carbon dioxide, water, oxygen etc. in the SOM-POF material. Such a sample is called the activated sample. To ensure the purity of 30 sample we degas it at 100°C and then perform the N 2 sorption measurements. From the sorption curves [ Fig. 2(b)] we calculated the BET and Langmuir surface area of the SOM-JUC-Z4 composite and found it to be 7.49 m 2 g -1 and 10.10 m 2 g -1 , respectively. On the other hand, the calculated BET and 35 Langmuir surface area of JUC-Z4 was found to be 793 m 2 g -1 and 979 m 2 g -1 , respectively. This means in the case of the composite, the surface area reduces almost 100 times which is attributed to the incorporation of heptamolybdate clusters in the POF pores. The pore size distribution derived from N 2 adsorption calculated 40 by DFT method [ Fig. 2 (b)] shows the average pore size of the composite to be around 2.73 nm which is inherited from its POF component-JUC-Z4. The 0.93 nm pore of JUC-Z4, however, is not observed in the composite. This indicates that the SOMs block the micropores of the POF whereas the mesopores remain 45 vacant. The existence of these mesopores of 2.73 nm provides the fine hierarchical pore structure which is suitable for catalysis.We also did N 2 adsorption measurements with SOM-PAF1, SOM-JUC-Z2 and SOM-JUC-Z5 composites and determined their BET surface area to be around 9.610 m 2 g -1 , 4.928 m 2 g -1 and 14.693 50 m 2 g -1 , respectively. In all these cases it is observed that the surface area is reduced almost 100 fold as in case of SOM-JUC-Z4, implying impregnation of soft-oxometalate units in the POF core-pores (See SI for details). 55

On heterogeneous catalysis by SOM-POF composites:
We now reiterate the question: can simultaneous abundance of phosphorous and molybdenum in a supramolecular structure lead to the emergence of catalytic behaviour comparable to that of the 60 molecular [PMo 12 ] Keggin? With this end in view we undertake a model reaction namely oxidation of benzaldehyde to benzoic acid with hydrogen peroxide using the SOM-JUCZ4 dispersion as a catalyst [ Fig. 3]. We observe that the SOM-JUC-Z4 dispersion is effective as a catalyst for the oxidation of benzaldehyde in the presence of 30% aqueous hydrogen peroxide using dimethyl sulfoxide (DMSO) as 95 an external standard. We monitor the reaction by time resolved Raman spectroscopy [ Fig. 3(b)]. The rate of formation of product benzoic acid increases with time in a sigmoid fashion [ Fig. 3 (c)] with respect to the added external standard DMSO and shows an initial lag phase of few minutes. Such a presence of lag phase and sigmoidal nature of product formation points to the operation of heterogeneous catalysis as 5 has been shown very nicely in the literature. [50][51][52][53][54][55][56][57][58][59][60][61] Indeed in the SOM-JUC-Z4 dispersion we observe composite particles which are a mixture of irregular shaped particles and nanotubes. They possess C, P, Mo and O on a nanoscopic scale in a homogeneous manner as observed from EDX-TEM from the SOM-POF 10 dispersion catalyzing the reaction [ Fig. 3(a)]. We speculate these are the active particles that are responsible for the heterogeneous catalysis we observe in the reaction. It is also worth noting the polydispersity in the system as well. In short we speculate that in a heterogeneous catalytic mode these particles of  55 The POF material i.e. JUC-Z4 alone did not show any activity whereas the SOM did show some catalytic activity but it was quite low as compared to the catalytic activity of the SOM-JUC-Z4 composite [Fig. 5]. This means that the SOM-component in 60 the composite is facilitating the catalysis however its efficiency is amplified in the presence of a porous material with fine accessible mesopores of 2.7 nm which provide the site for catalysis. In fact the supramolecular composite of SOM-JUC-Z4 shows a sort of synergistic effect arising out of SOM and POF 65 and its catalytic activity even surpasses the activity of our benchmark [PMo 12 ] polyoxometalate.   Fig. 6 Plot between ratio of intensity of acidic proton of benzoic acid peak and intensity of aldehydic proton of benzaldehyde peak versus catalyst loading from 1 H NMR studies. The reactions are in dispersions. 105

Comparative kinetic study of aliphatic and aromatic aldehydes oxidation using different SOM-POF composites in dispersion.
Our chosen model reaction system is that of benzaldehyde This comparative study showed that SOM-JUC-Z4 has maximum catalytic activity followed by considerable catalytic activity by molecular [PMo 12 ], SOM-JUC-Z5 and almost no activity by SOM-JUC-Z2 and SOM-PAF1. Such high activity by SOM-JUC-Z4 implies that indeed supramolecular combination of 5 phosphonium and molybdate is as effective in catalysis as elemental P, Mo in [PMo 12 ]. However it is worth noting that SOM-JUC-Z4 composite shows greater catalytic activity than the standard catalyst molecular [PMo 12 ] which is a known catalyst as well as a catalyst precursor for oxidation reactions [Fig. 7]. Such  40 electron microscopic characterization. Now having shown catalysis by SOM-POF dispersion, we wanted to take the next step. We ask: Can we induce a phase transition and pattern the SOM-POF dispersion and see the effect 45 it has on catalysis in a designed catalytic chip? Can we achieve a site-specific heterogeneous catalysis on such a designed catalytic chip? Now we address these questions. Recently we have shown that it is possible to write patterns using thermo-optical tweezers starting from a SOM dispersion by 50 inducing soft to crystalline phase transition. 12 Likewise a similar patterning by inducing phase transition in the freshly synthesized SOM-POF dispersion should also be possible. We thus place an aqueous SOM-POF dispersion in our sample holder described earlier. We place this sample holder on a movable scanning stage 55 and then focus 1064 nm laser light on the top surface of the sample holder. The SOM-JUC-Z4 composite has absorptivity of around 105 mol -1 cm -1 at 1064 nm. Hence, the laser light is absorbed by the composite, so that heating occurs at the focused spot in a localized manner. This, in turn, leads to formation of a 60 water vapour bubble from the water present in the medium. Since in the vicinity of the bubble no such heating has occurred, a temperature gradient is generated which causes convection current. These currents circulate the SOM-POF material and eventually deposit it at the base of the bubble. As the laser beam 65 is translated so that it focuses at a nearby new spot, there can be two possibilities. The first is that a new bubble is generated and the second possibility is that the previously formed bubble migrates to the new spot. Since the latter is thermodynamically more favourable, the initial bubble is also translated to the new 70 location of the laser focus and the chain of events that lead to the deposition of SOM-POF composite continues. In this way we are able to design a catalytic reactor chip comprising patterned trail [ Fig. 4(a)] having a width of few micrometres -a fact that is confirmed by the AFM studies [ Fig. 4(b)]. TEM measurement of 75 the patterned material is also carried out by scraping off the active catalytic material from the slide.  Now we test the catalysis of benzaldehyde oxidation by optically patterned SOM-JUC-Z4 composite on the chip. We use the 95 patterned material as a catalyst for benzaldehyde oxidation. We observe by time resolved Raman spectroscopy that the peak intensities of the product, benzoic acid with respect to external standard DMSO increases with time [ Fig. 8(a)]. However in addition to general bulk catalysis we checked the possibility of 100 site-specific catalysis on the patterned material surface using dimethyl sulfoxide (DMSO) as an external standard. Here we observe that indeed the reaction is catalysed much more efficiently on the patterned material surface in a site specific fashion. There is also a sigmoidal increase in the formation of We now compare and contrast the catalysis by the trail with the catalysis by the background using DMSO as an external standard. We observe the abundance of unreacted benzaldehyde from the non-patterned background using Raman spectroscopy [ Fig. 8(c)- (d)]. This is because after nucleation in the system and formation 5 of the trail there is a lack of active catalyzing particles in the nonpatterned background which loses the ability to catalyze the reaction as is obvious from AFM image of the background where no active catalytic particles are present. [Fig. 4(b)].  35 These observations have following aspects: 1. The trail is more efficient in catalysis and performs site specific catalysis. 2. The active particles of catalysis are the SOM-POF hybrid particles which are nanotubes and irregular particles in the dispersion and only nanotubes on the crystallized trail. Also note we observe 40 crystallization after laser irradiation from SAED-TEM as we have shown it elsewhere before. 12 3. Catalysis by both dispersion and the trail is heterogeneous in nature. 4. We can further pin-point that the active species in this catalysis are the rod-shaped SOM-POF nanotubes and irregular particles as seen and characterized 45 in detail by TEM-EDX elemental mapping from the active catalyst trail of the reactor catalyst chip. [Fig. 4(c)-4(e)] Since such particles are not present in the background of the catalytic chip, the background cannot catalyze the reaction [ Fig. 7(d)]. Both the sigmoidal kinetics of the reaction and the presence of 50 active particles show that the catalysis in dispersion and on the chip are heterogeneous in nature. 8. Comparison of catalytic activity of various optically patterned SOM-POF composite chips. 55 The catalytic activity of SOM-JUC-Z4 needs to be compared with other composites in order to do a comparative study of catalytic activity of SOM-POF materials. To accomplish this, patterned trails of SOM-PAF1, SOM-JUC-Z2 and SOM-JUC-Z5 60 were designed and these trails were used as sites for benzaldehyde oxidation in presence of hydrogen peroxide as oxidant. Their catalytic activity was compared in terms of ratio of intensity of benzoic acid peak and intensity of DMSO peak (external standard) obtained after the reaction by Raman 65 spectroscopy. We observe that SOM-JUC-Z4 patterned chip is the most effective in catalysis, even more than [PMo 12 ] benchmark [ Fig. 9]. This clearly indicates that supramolecular composite of patterned phosphonium with molybdate in SOM-JUC-Z4 is effective in catalysis. Since it has higher mesoscopic 70 accessibility as compared to [PMo 12 ], the SOM-JUC-Z4 patterned chip is more efficient in catalysis. After investigating the catalytic potential of the SOM-JUC-Z4 patterned chip the next step was to see the stability of this catalyst chip. For this purpose the trail was checked for its intactness by Raman spectroscopy post-reaction. It was found that the trail formed by SOM-JUC-Z4 gave the same Raman signatures as it 15 showed before the catalytic reaction thus indicating that the chip is stable and reusable after the reaction [Fig. 11]. The chip is also stable for weeks after its fabrication. 10. Comparative kinetic study of aromatic and aliphatic aldehydes oxidation using dispersion and patterned chips of SOM-POF composites as catalysts 40 The oxidation of different aldehydes viz., formaldehyde, acetaldehyde, furfural and benzaldehyde using all the five catalysts namely SOM-PAF1, SOM-JUC-Z2, SOM-JUCZ-4, SOM-JUC-Z5 and molecular [PMo 12 ] were studied in dispersion 45 phase in presence of hydrogen peroxide as oxidant. With the aid of time dependent 1 H NMR studies it was found that SOM-JUC-Z4 dispersion showed maximum catalytic activity for the oxidation of all the four aldehydes [ Fig. 7]. Among all the aldehydes, the SOM-POF dispersion showed higher selectivity 50 towards oxidation of benzaldehyde followed by formaldehyde, furfural and acetaldehyde, respectively [ Fig. 12]. For all the composites, we obtained sigmoidal curves in conversion kinetics which suggest heterogeneous catalysis. SOM-JUC-Z4 patterned chip was then used to catalyze oxidation of aliphatic aldehydes 55 such as formaldehyde, acetaldehyde and aromatic aldehydes namely furfural and benzaldehyde and it was monitored by time dependent Raman spectroscopy. The results obtained from the patterned catalyst chip were also quite similar to that of the dispersion phase catalysis. The rate of reaction of formaldehyde 60 oxidation was faster than that of furfural followed by acetaldehyde oxidation but the fastest oxidation was that of the benzaldehyde reaction. This implies that the chip formed by SOM-JUC-Z4 composite catalyzes benzaldehyde oxidation at the fastest rate [ Fig. 12]. showed that the highest rate of reaction for benzaldehyde oxidation was with dilute sulphuric acid. Hydrogen peroxide acted as the next efficient oxidant followed by dilute nitric acid and finally silver (I) oxide. (See Supplementary Information for more details) With the maximum product formation obtained in 5 case of SOM-JUC-Z4 catalyst for benzaldehyde oxidation in the dispersion phase, the patterned chip of SOM-JUC-Z4 was chosen to do a comparative study of aldehyde oxidation with the same set of four different oxidising agents, viz., silver (I) oxide, dilute nitric acid, dilute sulphuric acid and hydrogen peroxide. The 10 reactions were monitored by time dependent Raman spectroscopic experiments. It was observed that dilute sulphuric acid acted as the strongest oxidising agent. Hydrogen peroxide and dilute nitric acid showed comparable oxidising ability whereas silver (I) oxide oxidised benzaldehyde to a lesser extent 15 [ Fig. 14].

Conclusions
To summarize, we have shown that starting from a well defined molecular precursor of a heptamolybdate polyoxometalate, we first synthesized in a controlled way a soft oxomolybdate (SOM) nanotube. This in turn, forms another stable dispersion with a 35 well defined porous aromatic framework namely JUC-Z4. The composite material is characterized by detailed spectroscopic, gas sorption and microscopy experiments and indeed shows that, in the structure constituting the solid phase of the dispersion, there exist a simultaneous abundance of 40 phosphorous and molybdenum at nano scale. Hence we test our hypothesis: can this composite act catalytically in a comparable way to that of [PMo 12 ] Keggin? To do so, we use this composite for catalyzing oxidation of benzaldehyde to benzoic acid using hydrogen peroxide.We observe that not only 45 the dispersion catalyzes the reaction efficiently but also the patterned material comprising of SOM-POF composite. Moreover the catalysis on the surface of SOM-POF patterned material is more pronounced than that of the dispersion. We further show the operation of heterogeneous mode in catalysis 50 both in the dispersion and on the trail of the chip by observation of sigmoidal kinetics of product formation and by identifying the active catalytic particles. We also show when these particles are not present, as in the background of the catalytic chip, there is no catalysis. A comparative study of different composite materials as 55 dispersions and as chips for oxidation of different aldehydes using different oxidants has been done and based on the kinetic studies we can conclude that SOM-JUC-Z4 composite catalyzes oxidation of benzaldehyde in presence of hydrogen peroxide to the maximum extent even greater than molecular [PMo 12 ] . Such 60 high activity of SOM-JUC-Z4 vindicates two points. 1. Supramolecular composite comprising of phosphonium and molybdate is effective as catalyst. 2. High accessible mesopores of such composite compared to that of molecular [PMo 12 ] . is the reason for its high catalytic activity. This work in turn, implies 65 that it is possible to design a patterned composite material to catalyze deliberately targeted reactions starting from well defined molecular level precursors in a completely controlled fashion.