PROBLEM STATEMENT►Microporous zeolites having pore sizes smaller than 7Å cannot catalyse the Epoxidation of bulky organic molecules due to the inaccessibility to the actives located inside the micropores and strongly limits its application.
►To overcome this problem, the mesoporous material is used together with microporous zeolite as catalyst with incorporation of metal such as titanium and aluminium. The mesoporous material contains larger pores with diameter in range 2 to 50nm that would lead to lower diffusion limitation and having high thermal stability, so that it can withstands the high temperature as compared to the typical zeolites.
SIGNIFICANCE OF STUDY►Titanium containing silicates (zeolite catalyst) are the most efficient heterogeneous catalysts for epoxidation reactions and using hydrogen peroxide as an oxidant, which turns into water is an attractive method in the context of green chemistry.
GREEN CHEMISTRY►Heterogeneous catalysts are easy to separate from the product mixture and can be recycled.►Using a cheap and easily to get silica source in Malaysia using rice husk ash, (RHA) for synthesizing the mesoporous framework silica can reducing waste problem.
Homogenous Heterogeneous Catalyst Catalyst • Mineral acids • Non-toxic • Toxic • Environmental• Not environmental friendly friendly • Robust at high • Use of large temperature amount of catalyst • Recyclable • Non-recyclable
Composite Materials►Composite materials, often shortened to composites, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties.
Zeolites►Zeolites - important catalyst in production of fine chemicals and petroleum cracking due to their high acid strength and shape selectivity.►Possesses both Brönsted and Lewis acid sites.►However, the catalytic activity of zeolites are limited to small hydrocarbon molecules because of the small pore size (<2 nm).
M41S Family►Mesoporous silica - uniform, larger pore size (2-50 nm) and high surface area (>1000 m2g-1) are valuable in catalytic processes involving bulky organic molecules.►But low in acidity.►Does not posses any catalytic activities properties because silica framework is neutral and lack active sites.
Heterogeneous Catalyst Silica gel Zeolite M41SLow surface area Low surface area High surface area (< 1000 m2/g) (> 1000 m2/g)Non-porous Microporous (< 2nm) Mesoporous (2-50 nm)
Strategy Ti – Generate active sites for oxidation Al – Increase acidity of catalyst Larger pore diameter (2-50nm) Metal Lower diffusion limitation Mild acid strength Low hydrothermal stability M41S incorporation (Ti and Al) Zeolite Titanium - High acid strengthHigh acid strength aluminate High hydrothermal stability Larger pore diameterHigh hydrothermal stability containing Lower diffusion limitation Small pore diameter Diffusion limitation composite Active sites for oxidation catalyst of biporous catalyst
Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray (EDX) Analysis Zeolite NaY Si-MCM-48 Samples Si (%) Al (%) O (%) Na (%) C (%) NaY 28.74 12.71 33.45 8.54 16.56Si-MCM-48 61.56 1.47 36.98 - -
BET Surface Area Analysis Si-MCM-48(ac) 1000 NaY/Si-MCM-48 893.02 NaY/3Ti-Al-MCM-48 900 781.30 NaY/5Ti-Al-MCM-48 800 734.68 716.39 697.14 NaY/10Ti-Al-MCM-48 700Surface area 0.25Al-MCM-48 600 533.33 (m²/g) 487.50 NaY 500 Si-MCM-48(as) 400 300 180.67 200 100 Samples 0► amount of titanium, surface area►10.77% surface area loss when adding into 10% Ti from 0% Ti content.
Diffuse Reflectance UV Spectroscopy (DR UV-VIS) 269nm NaY/3Ti-Al-MCM-48 NaY/5Ti-Al-MCM-48 263nm NaY/10Ti-Al-MCM-48K-M 253nm190 Wavelength(nm) 400► Changes in titanium coordination (Tetrahedral Octahedral) from 253nm into 269nm when increasing titanium loading.
Transmission Electron Microscopy (TEM)MCM-48 Zeolite NaY
Catalytic Testing►The catalytic testing shows that the catalyst are successfully convert the 1-Octene into 1, 2 -Epoxyoctane and 1, 2 -Octanediol (side products) from epoxidation reaction.►The data from Gas Chromatography (GC) and Gas Chromatography-Mass Spectroscopy (GC-MS) are analyzed into %Conversion and %Selectivity of products.
Epoxidation of 1- Octene Catalyst [O]1 - Octane 1, 2 - Epoxyoctane H OH OH 1, 2 - Octanediol
►The rice husk ash (RHA) has been successfully acted as an active silica source for synthesizing ordered mesoporous material (Si-MCM-48).►Modifications of framework Si-MCM-48 by compositing with zeolite NaY with impregnation by titanium approaches has successfully synthesized with properties of microporous zeolite NaY, mesoporous Si-MCM-48 and Al-MCM-48.