Bhattacharyya, S. K.

Sinhamahapatra, P. K.

Sinhamahapatra, S.

English

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estimated. This value was used in the PPP schemeto calculate the ionization potentials of hvdro-carbons, and the results are presented in Table 1.Also given are the value!' obtained with the iiparameter. It is obvious that striking improve-ment occurs when ii. is replaced by o: The spectraltransitions are of course unaffecl ed by this replace-ment. Thus we are led to the conclusion thatsimultaneous agreement in transition energies andionization potential can be obtained, if a value ofcoulomb integral is used which is consistent withthe basis set assumed in the PPP model.References1. HOYLAND, J. R. & GOODMAN, L., J. chem. Phys., 33(1960), 946; 36 (1962), 12 and 21.2. FISCHER-H]ALMARS, I., Molecular orbitals in chemistry,physics and biology, edited by Lowdin & Pullman(Academic Press, New York), 1964, 361.3. FISCHER-H]ALMARS, I., J. cliem, Phys., 42 (1965), 1962.4. LINDERBERG, J., Chem. Pltys. Lett., 1 (1967), 39.5. JUG, K., Theoret. Chim. Acta (Berl.), 16 (1970), 95.6. WATANABE, K., J. chem. Phys., 26 (1957), 542.7. Quoted by SKANCKE, P. N., Acta chem. Scand., 18 (1964),1671.8. VVACKS, M. E. & DIBELER, V. H., J. chem. Phys., 31(1959), 1557.9. WACHS, M. E. & DIBELER, V. H., J. chem, Phys., 4(1<;64), 1661.10. BRIEGLAB, G. & CZEKALLA, J., Z. Electrochem., 63(1959), 6.11. KURODO, B., Nature, Lond., 201 (1964), 1214.12. CLARK, L. B., J. chem. Phys., 43 (1965), 2566.13. FINCH, A. C. ?vI., J. chem: Soc., (1964), 2272.14. BIRKs, J. B. & SLIFKEN, M. A., Nature, Lond., 191(1961), 761.15. MORRISON, J. D. & NICHOLSON, L. C., J. chem. Pltys.,20 (1952), 1021.Physicochemical Properties of SodiumMolybdate CatalystP. K. SINHAMAHAPATRA*, S. SINHAMAHAPATRAt &S. K. BHATTACHARYYADepartment of Chemistry, Faculty of ScienceBanaras Hindu University, Varanasi 221005Received 10 December 1976; accepted 3 April 1977Thermal characteristics of sodium molybdate(Na2MoO•.2H20) have been studied and the varioustransition products characterized by chemical ana-lysis, IR, X-ray diffraction, surface acidities, magneticsusceptibilities and surface area measurements.Sodium molybdate dihydrate undergoes endothermicchanges at 150°, 470°, 643° and 689°. The endothermictransitions at 150° are due to dehydration, at 4700 and643° account for crystal transformation and at 6890are due to melting. This compound contains acidsites in the pka range, +6·8 to -3,0. Medium acidsites (pka = +3,3) are reduced at 5100 whereas weakacid sites (pka ~ + 5·0) are increased at 6600 and above.The strong acid sites (pka~ +2·0) however, remain*Present address: Catalyst Section, Indian Institute ofPetroleum, P.O. III', Mohkampur, Dehra Dun 248005.To whom correspondence should be addressed.tPresent address: Oil Technology Division, Departmentof Applied Chemistry, University College of Science andTechnology, Calcutta 700009.NOTESalmost unchanged till melting. The pure molybdateas well as its thermal transition products are dia-magnetic. Surface area of the compounds decreasesconsistently as a function of calcination temperature.This decrease is suggested to be due to enlargementof micropores formed in individual sodium molybdatecrystallites due to sintertng.IT appears from a literature survey that catalyticactivity of SO~liU~lmolybdatel-6 has some depen-dence on Its calcination temperature. However, thesystematic studies on the thermal properties of thismolybdate are meagre. The present note dealswith. the differentia! thermal analysis (DTA), thermo-gravimetry (TG), Infrared (IR), X-ray diffraction(XRD), surface acidity, magnetic susceptibility andsurface area of pure as well as various thermaltransition products of sodium molybdate,DT A and TG of sodium molvbdats were carriedout by the methods reported earlier". For character-ization of the thermal transitions sodium molybdatewas calcined at 230°, 510°, 660° and 710° in airfor 2 hr in each case. IR spectra and XRD patternsof the pure as well as of the calcined samples wereobtai!led at room temperature by the methodsdescribed elsewheres. The surface acidic strength~is~ributio~ in .the above samples was measured by~nd~cator-tltratlO!l method using n-butylamine andI~d.I~a~ors of varIOUS PRa values". Magnetic suscep-t ibilit ios of the ~'3amples were determined by Faradaymethod at 24 USll1g Hg[Co(NCS)41 as calibrant.Surface areas of the samples were measured bylow temperature nitrogen adsorption BET method.!he composition of sodium molybdate, as reportedIS Na2Mo04.2H20.The DTA curve (not included) records a sharpendothermic peak at 1500 followed by three sharpendothermal changes at 470°, 643° and 689°. TheTG curve (not included) registers a total weight lossamoun!ing to ~5'1 % in the temperature range90-360. The weight loss (14'3%) Il1 the temperaturerange 110-60° corresponds to the removal of twomolecules of water from the molybdate. Thus, theendoth~rmic peak at 1500 is due to the dehydrationof sodium molybdate dihvdrate. However after160°, the weight loss registered in the TG c~rve isalmost negligible (0,8%) which probably accountsfor the removal of adsorbed traces of water.The bands observed in the IR spectrum of puresample at 3260 and 2220 crrr< are characteristic ofsymmetric and antisyrnmctric vO-H and aH-O-Hof lattice waterlO-12. The bands at 900 and 800cm-l are due to vMo--O characteristic of normalmolybdatests, The spectrum also reveals the pre-sence of bands at 1800, 1692, 1680 cm-l which areprobably due to overtone and combination bands.In the spectra of the samples preheated at 2300~nd above (up to 700°) a strong band at 830 em"!IS a~signed to V3 (ref. 14) and that at 1680 crrr" isattributed to first overtone of the band at 830 crrr".These bands are characteristic of pure Na2Mo04(ref. 14). X~I? patt~rn of the pure sample isreas.onably distinct WIth the characteristic lineshaving d = 6'829, 3'171, 3·050, 3·0, 2·1456 1.666A, etc., which compare excellently with' those741INDIAN J. CHEM., VOL. 15A, AUGUST 1977TABLE 1 - SURFACE ACIDIC STRENGTH DISTRIBUTION I~SODIUM ~IOLYBDATE CATALYSTSample= Surface n-Butylamine titre values] forarea indicators of various pka valuesm2/g+6'8 +5·0 +3'3 +2·0 -3,02·5 0'47 0·12 0·12 0·04 0·040·7 0·42 0·04 0·04 0·04 0·040'5 0·69 0·15 0·04 0·04 0·040·3 0'70 0·16 0·04 0·04 0·04SM 230SM 510SM 660SM 700*The arabic numeral signifies the temperature at whichsodium molybdate has been calcined.[The values are expressed as mmolesjg ; accuracy ±0·01.reported for Na2Mo04.2H20 (ASTM Card No. 1-0113).Diffraction pattern of the sample heated at 230°is slightly different and shows the presence of afew new strong lines having d = 5'405, 3·263, 2'765,1·865, 1'756, 1·612 A, etc., resembling closely thosereported for standard patterns of Na2Mo04 (ASTMCard No. 12-773). Therefore, the endothermic peakat 150° is clearly due to dehydration of theNa2Mo04.2H20. The structure of the dehydratedsample appears to be more crystalline than that ofthe hydrated one. XRD pattern cloes not undergoany significant change when the molybdate iscalcined at 510° and above. The last endothermicpeak at 689° is, however, due to melting. Thetwo peaks at 470° and 643° may be associatedwith crystal transformation as these changes arenot accompanied by any weight change when heatedat 470° and above.Na2Mo04 is known to exist!" in four modifications.The ec-form is stable above about 620°: the ~-formbetween 620° and 580°; Y-form between 510° and410°; and the ii-form below 410°. Thus, the endo-thermic transitions at 473° and 643° are due to thefollowing transformation:470" 643"iI-Na2Mo04 ----;. Y-Na2Mo04 -~ IX-Na2Mo04The transition between 620° and 580° could not beobserved in the DTA curve and hence it is difficultto show the presence of ~-Na2Mo04'Surface acidic strength distribution in sodiummolybdate samples is shown in Table 1. It isobserved that the medium acid sites (Pka = +3,3)are reduced as the molybdate is calcined at 510°.The strong acid sites (Pka ~ +2,0), however,remain almost unchanged np to melting. It isinteresting to note that weak acid sites (Pka ~ +5'0)increase at 660° and above. The acidic strength ofMo03.Fe2(Mo04b at Ho s; +4·0 has been reported byPernicone et al.16• They found this molybdate toexhibit varying acid content as a function ofcalcination temperature. The maximum acidity,0·06 mmolejg, was found at 500°. Thereafter, asteady decrease was observed up to 700°. At 400°,acidity value at Ho ~ +4·0 was <0·04. Theseacidities were found to have a close correlationwith catalytic activity of Mo03.Fe2(Mo04)~ in theoxidation of formaldehyde. Sodium molybdate,being oxidation catalyst for many reactions+", mayalso be expected to use its acidities in the oxidation.742Surface areas of the heat-treated samples ofsodium molybdate are given in Table 1. It is seenthat '~hen sodium molybdate dihydrate is heated,there :5 a consistent decrease in the surface area:vhi.c~ may be due to the fact that on heating, th~IlldIVId':1alsodium molybdate crystals get dehydratedand shrink, thereby increasing the interparticle poresor more appropriately the micropores (dehydrationpores) .formed in individual sodium molybdatecrys~alhtes may. enl~rge due to sintering, therebycausing a reduction III surface area.l\~agnetic measurements reveal that the puresodium molybdate dehvdrate as well as its thermaltransition products are' diamagnetic.References1. S~I.TALSKII' E. & FUNCK, A., Z. phys. Chem., 126 (1927),2. Netherland Pat. 413,733 (1965), to Imperial ChemicalIndustries Ltd.3. Bclg. Pat. 669,981 (1966) to E. 1. du Pont.4. YATSIMIRSKII, K. B. & FILIPPOV, A. P., Zh. neorg.Khim., 9 (1964), 2096.5. Netherland Pat. 405,089 (1964), to Pennsalt ChemicalsCorporation.6. WILLIAMSO~, J. B., Brit. Pat. 1,003,347 (1965).7. BHATTACHARYYA, S. K., RAMACHANDRAN, V. S. &GHOSH, J. C., Adv. Catalysis, 9 (1957), 114.8. SINHAMAHAPATRA, P. K. & BHATTACHARYYA, S. K.,J. thermal Analysis, 8 (1975), 45; 9 (1976), 279; cu«.Era, XII (3) (1976), 79.9. HIRSCHLER, A. E. & SCHNEIDER, A., J. chem. engngData, 6 (1961), 313.10. GAMO, 1., Bull. chem. Soc. Japan, 34 (1961), 760, 765,1430, 1433.11. ZECCHINA, A., COLUCCIA, S., GUGLIELMINOTTI, E. &GHIOTTI, G., 1- phys. Chem., 75 (1971), 2774.12. DOUGLAS, R. M., Acta Cryst., 10 (1959), 423.13. NAKAMOTO, K., Infrared spectra of inorganic and co-ordination compounds (John Wiley, New York), 1963,159.14. BUSEY, R. H. & KELLER, O. L. (Jr), J. phys. ci-«,41 (1964), 125.15. MELLOR, J. ve.. A comprehensive treatise on inorganicand theoretical chemistry, Vol. 11 (Longmans, London),1962, 553.16. PERNICONE, N., LIBERTI, G. & ERSINI, L., Proceedingsof 4th international congress on catalysis, Moscow,Reprints of paper No. 21, 1968.Effect of Triton X-tOo on the Kinetics ofIrreversible Electrode Processes:Polarographic Behaviour ofNi(II), Co(II), Zn(lI) & Mn(I1)SUDHINDRA SWARUP SHARMA, S. K. JHA & MUKHTAR SINGHDepartment of Chemistry, Agra College, AgraReceived 30 November 1976; accepted 21 February 1977Polarographic behaviour of Ni(II), Co(II), Zn(II)and Mn(II) has been studied in O'IM KN03 in thepresence of increasing concentrations of Triton X-tOO(0'0-0'01 %). The values of the kinetic parameters kj,hand ana) have been calculated by Koutecky's treatment.The well established irreversible electrode processesof Ni(II) and Co(U) become more irreversible withan increase in [Triton X-IOO]. The quasi-reversibleelectrode processes of Zn(II) and Mn(II) becometotally irreversible with increasing [Triton X-tOO].

Physicochemical Properties of Sodium Molybdate Catalyst

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Physicochemical Properties of Sodium Molybdate Catalyst

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