NGHIÊN CỨU PHẢN ỨNG CỦA p-XYLEN

TRÊN CÁC XÚC TÁC TiO₂ KHÁC NHAU

 

Trần Thị Vân Phượng¹, Nguyễn Quốc Tuấn², Hòang Anh Thư¹,

Hồ Thị Cẩm Hoài¹, Lưu Cẩm Lộc²

¹ Khoa Hoá học, Trường Đại học Khoa học Tự nhiên

² Viện Công nghệ Hoá học, Viện Khoa học và Công nghệ Việt nam

Tóm tắt:

 

            Bốn mẫu xúc tác TiO₂ ( ST 01, ST 21 chứa 15 % ZnO, ST 31, ST41) của Ishihara Sangyo Kaisha) và một mẫu P25 của Degussa tẩm trên que đũa thủy tinh được nghiên cứu trong phản ứng quang  oxy hóa p-xylen trong pha khí tiến hành trong điều kiện dòng vi lượng tại 40 ^oC có chiếu tia UV.  Các kết quả thực nghiệm thu được cho thấy có ảnh hưởng của kích thước hạt, thành phần xúc tác, nhiệt độ và điều kiện họat hóa lên họat độ và độ bền của xúc tác.

 

 

A STUDY ON TiO₂ OF DIFFERENT COMPOSITION

IN PHOTOCATALYTIC OXIDATION OF p-XYLENE

 

Tran Thi Van Phuong¹, Nguyen Quoc Tuan², Hoang Anh Thu¹,

Ho Thi Cam Hoai¹, Luu Cam Loc²

¹ Faculty of Chemistry – University of Natural Sciences

 

Abstract:

 

            Four samples of TiO₂ (ST 01, ST 21 containing 15% ZnO, ST 31, ST 41 of Ishihara Sangyo Kaisa) and a sample P 25 Degussa have been studied in photocatalytic oxidation of p-xylene. The reaction was carried out at 40^oC in a microcatalytic reactor under the ultraviolet (UV) lighting. The physico-chemical properties of catalysts were characterized by the methods of nitrogen adsorption (method BET) and X-ray diffraction (XRD). The samples of particle size below 7 nm (ST 01, ST 31) characterized by much higher values of specific surface area compared with other samples (particle size ³ 20 nm), but these quantities decreased very fast with temperature of treatment. No changes were observed in the ratio anatase/rutile in  samples ST 01, ST 31, ST 21 and ST 41 (samples contain 100% of anatase phase at origin) as well as sample P 25 (sample contains 20 % rutile at origin). Also the values of p-xylene adsorption on samples with small particle size has been noticed to be lower than those on samples with bigger particle sizes. All the given observations have been interpreted by the thermal stability of catalysts, including the influence of ZnO content.

            The photocatalytic activity of catalysts were determined after thermal treatment as well as UV lighting. The common observation is that the higher temperature of treatment the lower conversion of p-xylene obtained. This fact should be related to the decrease of specific surface area with increase of temperature. This remark is evidenced by the fact of lower activity of the samples with smaller particle size. UV lighting treatment of the catalysts led to higher p-xylene conversion at the starting moment but the activity decreased with a higher rate compared with the cases when the catalysts treated by temperature. It is interesting that this fact is coinsided with the observation of higher carbonaceous deposition on the samples treated by UV treatment. In general high cabonaceous deposition was observed on the samples with big particle sizes (> 20 nm); the less particle size of the catalyst the weaker carbonaceous deposition. This fact can be explained by the particle size sensibility of the processes leading to intermediate products instead of forming final products CO₂ and H₂O.

            It has been found that the higher temperature of catalysts treatment the lower photocatalytic activity of the system. This observation should be explained by the reduction of specific surface area. It could be noticed also that the existence of ZnO in sample ST 31 would be a reason of its low activity and high capability in cabonaceous deposition.