Sinhamahapatra, P. K.

Sinhamahapatra, S.

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found to be about 5% (0·034 meqjg) and 9% (0·056meq/g) respectively, whereas the weak acid sitesconstitute about 85% (0·27+0·29 meq/g) as shownin Table 1. Impregnation of pure alumina with0·5% by weight of lithium ion brings dcwn thestrong and medium acids by about 70 and 40%respectively, at the same time it increases the weakacids by 15%. Lithium ion content >0'5% eli-minates completely the streng and medium acidsites, while the amount of weak acid sites showsa continuous increase. In other words lithium ienaddition seems to modify the streng acid sites intoweak acid sites, keeping the total acidity cc nstant(Table 1). Herman Pines" has also abserved asimilar effect on the additien of scdium ien toalumina catalyst.On the other hand modificatixn of pute aluminawith 2% hydrofluoric acid enhances significantlythe strong and medium acids by 370% (0·160 meq/g) and 340% (0·260 meq/g) respectively, whereasthe enhancement in the case of weak acids is cnlvabout 78% (Table 1). Increase of hydrofluoric acidbeyond 2% seems to have no effect on weak acidsbut the strong and medium acids continue to increasewith hydrofluoric acid. It is to be noted that unlikelithium ion which keeps the total acidity ccnstant ,hydrofluoric acid increases the total acidity.The author thanks Dr G. S. Laddha for facilitiesand encouragement.References1. HIRSCHLER, A. E. & SCHNEIDER, A., I chem. Engng Data,6 (1961), 313.2. BENESI, H. A.. I phys. Chem., 61 (1957), 970.3. PINES, H. & HAAG, W.O., I Am. chem, Soc., 83 (1961),2847.4. MAcIVER, D. S., BRIDGES, l M. & RYMER, G. T., I pbys,cis«, 66 (1962), 871.5. PINES, H. & CHEN, G. T., I Am. chem, Soc., 82 (1960),2471.Physico-chemical Properties of SodiumTungstate CatalystP. K. SINHAMAHAPATRA* & S. SINHAMAHAPATRAtDepartment of Chemistry, Faculty of ScienceBanaras Hindu University, Varanasi 221005Received 9 September 1976; accepted 13 December 1976Thermal characteristics of sodium tungstate,NaZW04.2H20 have been Investigated by DTA and TG,and various transition products analysed by chemicalanalysis, IR, X-ray diffraction, surface acidity andmagnetic susceptibility techniques. This tungstateundergoes endothermic changes at 150°, 600° and 700°which are asstgned to dehydration, crystal trans-formation and melting, respectively. The compounddoes not undergo any decomposition till rnettlng.The pure tungatate as well as its transition productsare dlamagnetlc and do not contain acid sites.- _._---._----·Present address: Catalyst Section, Indian Institute ofPetroleum, P.O. LI.P., Mohkampur, Dehra Dun 248005.(To whom correspondence to be made.)tPresent address: Oil Technology Division, Departmentof Applied Chemistry, University College of Science &Technology, Calcutta 700009.NOTESSODIUM tungstate has been used as a catalyst inthe isomerization of iodides by hydrogen per-oxide>, decomposition of hydrogen peroxide>, de-hydration of formamide" to hydrogen cyanide at250-510°, tridymite formation from quartz+, vinylacetate productic n! and in the decomposition ofbenzil by hydrogen peroxide". As the activity ofa catalyst depends mainly on its physicochemicalproperties, it is worthwhile to study some of theprcperties of scdium tungstate. The present notedeals with thermal analysis (DTA and TG), infrared(IR), X-ray diffraction (XRD), surface acidity andmagnetic susceptibility of sodium tungstate as wellas of its thermal transition products.DT A and TG of sodium tungstate were carriedout as reported earlier 7. IR spectra and XRDpatterns of the pure sample as well as of its thermaltransition products obtained by calcining the com-pound at 250°, 660° and 710° in air for 2 hr in eachcase, were obtained by the methods describedearlier", Magnetic susceptibilities of these sampleswere measured by Faraday method at 24° usingHg [CO(NCS)4J as cali brant. The surface acidicstrength of the samples was measured using n-butylamine and Ho indicators", Na" and W6+ insoluticn were estimated by conventional methods.The amount of water was determined using Colemancarbon-hydrogen analyser.The composition of the catalyst, as reported, isNa2W04·2H20.DT A and TG curves of sodium tungstate areshown in Fig. 1. The DTA curve shows one endo-thermic peak at 150° (range 100-220°) followedby two sharp endothermic changes at 600° and700°. The TG curve represents a gradual weightloss starting from 100° and ending at 220°, thetotal weight loss being 11'6%, corresponding to the+s~v 0~z -5 OTA0;:~ -10 0-'..~ -'5 I~-20 2 600°0-W 700·~ -25 ;,Z 14S· 200-c> 4-'C" 557o-t8.;-9'"0 T6-'..'0x";; ..:.'2100 200 ;'00 4()0 500 600 100TfMPfRATURI!: •or.Fig. 1 - DTA and TGA of sodium tungstate dihydrate349INDIAN J. CHEM., VOL. 15A, APRIL 1977removal of two molecules of water. Therefore,the endothermic peak at 150° in DTA curve is dueto the loss of two molecules of water thereby givinganhydrous sodium tungstate. The TG curve neitherindicates the possibility of forrnatic n of any inter-mediate stage during dehydration nor exhibitsany significant weight-change in the temperaturerange 220-750°. Hence, the endothermic changesat 600° and 700° are due to some precesses whichdo not accompany any weight change.The pure sample exhibits IR bands at 930 and800 ern? which may be assigned to the 'JW-O ofnormal tungstates!". The other bands appeal ingat 3300-1600 crrr+ region are due to symrnct: ic andantisymmetric 'IO-H and oH-O-H of lattice waterll-13.The tungstate appears to be completely dehydratedat 250° as indicated by the absence of characteristicbands due to water molecules. Therefore, theendothermic change at 150° is clearly due to de-hydration. The significant observation at and after250° is that the band at 800 crrr ' shifts to 830 em"!with enhanced intensity followed by the dis-appearance of the 930 cm! band. Thus, the strongband of ST 250 (sodium tungstate calcined at 250°)sample at 800 crrr- may be expected to be coupledwith frequency, characteristic of water. As theIR bands of the samples ST 660 and ST 710 arealmost the same as those of S1'250, it can be suggestedthat the endothermic changes after 250° are notdue to decomposition of the tungstate rather dueto phase changes. The last endothermic peak at700° is, however, due to melting.The pure sample exhibits a well defined XRDpattern with characteristic lines at d=6·95, 6'0,5·3, 4'2, 3·6, 3·3, 3·17, 2'98, 2'17, 2·12 A, etc.On comparison with the d-values given in ASTMCard No. 1-011 for the standard patterns of sodiumorthotungstate(VI) dihydrate it is seen that thesample is pure Na2W04. 2H20. XRD patternsof the catalyst are little changed at and after 250°with the registration of strong lines at d=5·25,3'21, 3·16, 2·75 A, etc. The d-values of the ST250, ST 660 and ST 710 samples compae excellentlywith these reported in the ASTM Ca-d 1\0. 5-0247for Na2W04 (d=5·19, 3'18, 2·72 A, etc.), indicatingthat the endothermic change at 150° is due to de-hydration and those after 250° are due to cry~taltransformation. Earlier workers also found sodiumtungstate to undergo the following phase changesat the temperature region 431-700°:431-587° 587-700°o-Na2W04---+ Y-Na2W04----+~-N "2W04The present studies, however, reveal that sodiumtungstate does not undergo any phase change inthe temperature range 431-570°. The temperaturerange at which phase changes take place, seems tobe 570-700°. Magnetic measurements indicate thatthe pure sodium tungstate as well as its thermaltransition products are diamagnetic. Surface aciditymeasurements reveal that this tungstate does nothave surface acidic sites at any stage of thermaltreatment. This study also rules out the porsibilityof the decomposition reactir n Na2WO 4-;> Na20 +W03'till the melting of the tungstate as W03 is knownto have a good number of surface acidic sites.350References1. YATSIMIRSKII, K. B. & MOROZOVA, R. P., Kinelika bKataliz, 4 (1963), 574.2. SPITALSKII, E. & FUNCK, A., Z. physik. Chem., 126(1927), 1.3. FELLOWS, L. & MELLEHS, E. V., Brit. Pat. 584,598(1947).4. INUZUKA, H., J. Japan Assoc. mineral petrol., econo.Ceol., 26 (1947), 200; Chern. Abstr., 42 (1948), 65i.5. Imperial Chemical Industries Ltd, Netherland Pat.413,733 (1965).6. KWART, H. & WEGEMER, N. J., J. Am. chem. Soc., 87(1965), 511.7. BHATTACHARYYA, S. K., RAMACHANDRAN, V. S. &GHOSH, J. C, Adv. Catal., 9 (1957), 114.8. SINHAMAH,\PATRA, P. K. & BHATTACHARYYA, S. K.,J. thermal Anal., 8 (1975), 45; SI:<lHAMAHAPATRA,P. K. & BHATT ACHARYYA, S. K., Chern. Era, XII (3)(1976), 79.9. HIRSCHLER, A. E. & SCHNEIDER, A., J. chem, EngngData, 6 (1961), 313.10. NAKAMOTO, K., l nfrared spectra of inorganic andcoordination compounds (John Wiley, New York),1963, 159.11. GAMO, 1., Bull. chem. Soc. Japan, 34 (1961), 760, 765,1430, 1433.12. ZECCHlNA, A., COLUCCIA, S., GUGLIELMINOTTI, E. &GHIOTTI, G., J. phys. cu«; 75 (1971), 2774.13. DOUGLAS, R. M., Acta Crystallogr., 10 (1959), 423.14. MELLOR, J. W., A comprehensive treatise on inorganicanti theoretical chemistry, Vol. II (Longmans, Green,London), 1931, 774.Thermal Decornposttion of Gamma-irradiatedBarium BromateS. D. BHATTAMISRA & S. R. MOHANTYNuclear Chemistry Laboratory, Utkal UniversityBhubaneswar 751004rteceiued 20 September 1976; accepted 29 November 1976The effect of ~amma-lrradiation of barium bromateis to shorten the induction period and increase therates of its decomposition in the linear, acceleratory,and decay stages, The activation energy of the linearreaction decreases under irradiation and that of theacceIeratory stage increases whereas the activationenergy of the decay stage remains unaffected.DUKE and ::,hute1 found that the decompositionof potassium bromate catalysed by bromideion in fused alkali nitrates was first order with re-spect to both bromate and bromide. Jach2,3 hasshown. that whereas the isothermal decompositionof sodium b: ornate followed a contracting envelopeformula that of pctassium bi cmate cccun cd acccrd-ing to a first order rate law. Both these substancesundergo fusion when sufficient bromide accumulatesduring the course of the decompositic n because ofwhich ,a dis~on~inu~ity cccurs in the Arrhenius pk. ts.The discontinuity IS removed by Y-irradiatic n in thecase o~ pota~sium bromate. The present workdeals WIth the influence of irradiation on the isother-mal decompositicn of barium bromate which takesplace throughcut in the solid ccnditic n.AR grade barium bicmate, dried! at 170° wasirradiated in sealed glass ampoules with 60(0 1-rays to various doses up to 420 Mrad at rocm tern-

Physico-chemical Properties of Sodium Tungstate Catalyst

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Physico-chemical Properties of Sodium Tungstate Catalyst

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