Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 118, Issue 12, Pages 6226-6234Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp411405r
Keywords
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Funding
- King Abdul Aziz City for Science and Technology [649-32]
- National Natural Science Foundation of China
- China National Petroleum Corporation [U1362202]
- National Natural Science Foundation of China [21206195]
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The objective of this work is to investigate the surface acidity of gamma-Al2O3 after modification and its application in reducing coke formation in the fluid catalytic cracking (FCC) process. gamma-Al2O3 with rich Bronsted acid sites and reduced Lewis acid sites was prepared by the sol gel method using NH4BF4 as a modifier to develop a new functional material to adjust surface acidity. N-2 sorption, powder X-ray diffraction (XRD), Al-27 magic angle spinning nuclear magnetic resonance (Al-27 MAS NMR) spectroscopy, X-ray. photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR) spectroscopy were used to characterize the structure and surface properties of the prepared gamma-Al2O3. The results showed that partial fluorination of the surface of gamma-Al2O3 generated small quantities of a pyrochlore-type phase which was formed mainly by substitution of the OH group on six-coordinated aluminum with fluorine. In addition, boron insertion in the structure of gamma-Al2O3 reduced the Lewis acid concentration and increased the surface area of gamma-Al2O3. After aging in an alkaline solution with a F/Al mole ratio of 0.45, the modified gamma-Al2O3 demonstrated high surface area (276 m(2)/g) with gamma alumina structure due to the synergistic effect of boron and fluorine doping by using NH4BF4. However, most importantly the modified gamma-Al2O3 exhibited the high Bronsted/Lewis acid ratio of 0.75. In the bench-scale tests with heavy oil, the modified gamma-Al2O3 showed good catalytic performance by increasing conversion of heavy oil to light oil while reducing coke formation.
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