Sains Malaysiana 41(10)(2012): 1245–1251

Effects of Titration Parameters on the Synthesis of Molybdenum Oxides Based Catalyst

(Kesan Parameter Penitratan terhadap Sintesis Mangkin Molibdenum Oksida)

D.D. Suppiah*, F.A. Hamid, M.G. Kutty & S.B. Abd. Hamid

Combinatorial Technology and Catalysis Research Centre (COMBICAT)

Level 3, Blok A, Institute of Postgraduate Studies, University Malaya

50603 Kuala Lumpur, Malaysia

Diserahkan: 11 Ogos 2011 / Diterima 4 Mei 2012

ABSTRACT

Molybdenum oxides catalysts are extensively used in various selective oxidation reactions. In this work, controlled precipitation method was used to synthesise molybdenum oxides. The effects of various titration parameters on the precipitate growth rate and structure throughout catalyst synthesis were investigated. The titration parameters varied for this study were molybdates (ammonium heptamolybdate) concentration, precipitation agent (HNO3) concentration, precipitating agent rate of addition and temperature of synthesis. X-Ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM) were used to characterize the catalysts. This study highlights the significant effects of the titration parameters varied on the supersaturation of the solution therefore yielding precipitate with different morphology. It was observed that the temperature played the major role followed by molybdate concentration in the formation of the bulk catalyst. Supramolecular structure (Mo36O112) was observed at lower temperature (30ºC) and lower molybdate concentration (0.07 M, 0.10 M) while at higher temperature (50ºC) and higher molybdate concentration(0.14 M) hexagonal (h-MoO3) phase structure was formed. Fast rate of addition and high concentration of precipitating agent affected the solution equilibrium leading to unclear inflection point (supersaturation point) at the titration curve.

Keywords: Catalyst; molybdenum oxides; precipitation; titration

ABSTRAK

Mangkin molibdenum oksida digunakan secara meluas dalam pelbagai tindak balas pengoksidaan terpilih. Kaedah pemendapan yang terkawal telah digunakan dan pelbagai parameter penitratan telah digunakan seperti kepekatan molibdat (ammonia heptamolybdate), kepekatan agen pemendapan (HNO3), kadar penambahan agen pemendapan dan suhu sintesis. Kesan setiap parameter terhadap kadar pertumbuhan dan struktur zarah semasa sintesis mangkin telah dikaji. Pembelauan sinar-X (XRD) dan Mikroskop Pancaran Medan Elektron Imbasan (FESEM) digunakan untuk mengenal pasti ciri-ciri mangkin. Berdasarkan kajian yang telah dibuat, perkara utama yang perlu diberi perhatian adalah kesan setiap parameter penitratan terhadap keterlarutan yang menghasilkan pemendapan pepejal dengan morfologi berbeza. Suhu memainkan peranan paling penting diikuti kepekatan molibdat dalam pembentukan mangkin pukal. Struktur supramolekular (Mo36O112) telah diperhatikan pada suhu rendah (30ºC) dan kepekatan molibdat rendah (0.07 M, 0.10 M) sedangkan pada suhu tinggi (50ºC) dan kepekatan molibdat tinggi (0.14 M) struktur hexagonal (h-MoO3) telah dihasilkan. Kadar penambahan yang cepat dan kepekatan tinggi agen penitratan mempengaruhi keseimbangan larutan dan mengakibatkan titik keterlarutan yang tak jelas.

Kata kunci: Mangkin; molibdenum oksida; pemendapan; penitratan

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*Pengarang surat-menyurat; email: d_devi10@yahoo.com