Characterization of MOCVD TiO2 coating and its anti-coking application in cyclohexane pyrolysis

• The deposition kinetics of TiO2 coating varied with reaction temperature and time.
• The TiO2 coating deposited at 250 °C has the best anti-coking performance.
• The deposition kinetics of TiO2 coating influences its anti-coking performance.

In order to inhibit the surface coking, TiO2 coatings were prepared on the 310S stainless steel surface by the metal-organic chemical vapor deposition method in a horizontal hot-wall tubular reactor under atmospheric pressure condition. According to the coating deposition kinetics, the apparent activation energy of 29.30 kJ/mol was obtained in the low temperature range from 250 to 400 °C due to the domination of the surface reaction. However, the coating deposition rate declined at temperatures above 400 °C because of the simultaneous generation of TiO2 powder in the gas phase. The morphology, elemental and phase composition of TiO2 coatings were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. The results show that the surface TiO2 particle size increased with the rising temperature, and anatase phase was achieved above 350 °C with the preferential growth of crystal structure from (101) face at 350 °C to (220) face at 450 °C. Correspondingly, the coating thickness increased with the deposition time, and the coating with the thickness of about 2 μm covered the substrate surface completely, with the elemental composition in atomic percentage of Cr, Fe and Ni being close to 0, respectively. Based on the parallel experiments of cyclohexane pyrolysis for each TiO2 coating specimen, it is indicated that the best performance was achieved on TiO2 coating deposited at 250 °C for 80 min with an anti-coking ratio of 64.0%. The ratio was 48.0% for that deposited at 450 °C for 30 min. And the coating deposited at 450 °C for 30 min has better effect on inhibiting the formation of filamentous carbon.