NF3 decomposition over some metal oxides in the absence of water

Available online at www.sciencedirect.com| Joumal ofScienceDirect7I Natural GasChemistryEL SEVIERJournal of Natural Gas Chemistry 19(2010)463- ,467www.elsevier.com/locate/jngcCommunicationNF3 decomposition over some metal oxides in the absence of waterXianjun Niu, Liang Sun，Yanan Wang,Haipeng Wu，Xiufeng Xu*School of Chemistry and Biology, Yantai Universit, Yantai 264005, Shandong, China[ Manuscript received May 31, 2010; revised August 20, 2010 ]AbstractNF3 decomposition in the absence of water over Al2O3, Fe2O3, Co;O4 and NiO, and transition metal oxides (Fe2O3, Co3O4 and NiO) coatedAl2O3 reagents was investigated. The results show that Al2O3 is an active reagent for NF3 decomposition with 100% conversion lasting for8.5 h at 400 °C. Fe2O3, Co3O4 and NiO coated Al2O3 reagents are superior to bare Al2O3, and 5%Co3O4/Al2O3 has a high reactivity withNF3 full conversion maintaining for 10.5 h. It is suggested that the presence of transition metal oxide is beneficial to the reactivity of Al2O3,and results in a significant enhancement in the fluoriz ion of AlKey wordsNF3 decomposition; metal oxides; Al2O3; reactivityNF3 is used as a novel etching and cleaning. .A.Aal element was 5% relative to Al2O3.conductor industry, which has a global warm Ing potenta1ll decom posit o rpactions over the single metal oxides and tran-(GWP) of 17200 times relative to CO2 and a atposphetgthoynelaliles coated Al2O3 reagents in the absence oflifetime of 740 years [1]. Due to more and f brelemssolI I wo were Carried out in a fixed-bed reactor at 400 °C underof NF3 into atmosphere, it is strongly requiredtodestruct theatmospheric pressure. Approximately 2g (20-40 mesh) re-NF3 molecules exhausted from industrial processes.gent was placed inside an Inconel tube reactor, and 2 vol%NF3As reported, metal phosphate catalysts are effective ondiluted in He was passed over the reagent with a flow rate ofNF3 destruction in the presence of water [2,3], but the HF50 m/min. The effluent gas was separated and monitored byproduct is very corrosive to the reactors. In contrast, NF3 de-a gas chromatograph (GC-950, Shanghai Haixin) equipped bycomposition without water over some metal oxides is a simplea HayeSep D column and a thermal conductivity detector. Theand economical method for the abatement of NF3. Vileno et reactivity of metal oxides is expressed by NF3 complete coal. [4] reported the thermal decomposition of NF3 over alu-version time.mina, HX zeolite and calcium oxide, and found that the de-The BET surface areas of Al2O3, Fe2O3， Co3O4 andcomposition of NF3 on alumina can occur at the temperatureNiO measured using an automated nitrogen adsorption apas low as 100 °C with steady complete conversion of NF3 forparatus (NOVA3000, Quantachrome) are 127.8, 14.0, 28.5,about 4 h at 400 °C. Except for Vileno's work, no other liter-11.9 m2/g, respectively. Figure 1 gives the NF3 conversionature about NF3 thermal decomposition over metal oxides hascurves over these metal oxides, it is clear that NF3 can decom-been found. Fortunately, the results of CCl4 and chloroflu-pose completely over Al2O3 with NF3 conversion of 100%orocarbons (CFCs) decomposition without water reported inlasting for 8.5h at 400 °C. The reactivity of Fe2O3, Co3O4References [5- 19] give many suggestions to study the de-and NiO is lower than that of Al2O3. It can be seen thatstruction of NF3.the metal oxide converted to metal fluoride after reactionIn the present work, several single metal oxides, such asfrom XRD (Shimadzu XRD-6100, Cu Ka radiation) patternsAl2O3, Fe2O3, Co3O4 and NiO, were prepared by precipita-shown in Figure 2. Al, Fe and Ni elements have no changetion method, and several transition metal oxides coated Al2O3,in valence, while part of Co element was reduced from va-such as Fe2O3/Al2O3, Co3O4/Al2O3 and NiO/Al2O3, wereence (I) to valence (II), indicating that the chemical reac-prepared by incipient wetness impregnation of Al2O3 withtions listed in Equations (1)-(4) took place during NF3transition metal nitrate solutions, where the weight percentagedecomposition. From the A,G0 and A.H0 values of these* Corresponding author. Tel and Fax: +86-535-6902233; E-mail: xxf@ ytu.edu.cn中国煤化工This work was financially supported by the National Natural Science Foundation of China (No. 205MHCNM HGCopyrightO2010, Dalian Institute of Chemical F, ChineAcademy of Sciences. All rights reserved."doi:10. 1016/S 1003-9953(09)60107-9w.st,464Xianjun Niu et al./ Journal of Natural Gas Chemistry Vol. 19 No.52010lowing experiment, the Al2O3 samples were coated by tran-free energy and exothermic effect in the reactions betweensition metal oxides in order to increase their reactivity in NF3NF3 and the metal oxides, clearly indicating that these reac-decomposition.tions are thermodynamically preferable.2NF3+Al2O3 = NO+NO2+2AIF300 tA,G0= -489.6 kJ/mol, ArH0= -488.2 kJ/mol (1)2NF3+Fe2O3 = NO+NO2+2FeF380入A,G0=-441.6 kJ/mol, A,H0=-435.9 kJ/mol (2)604NF3+2Co3O4 = 2NO+2NO2+O2+6CoF2A,G0=-382.9 kJ/mol, A,H0 = -358.5 kJ/mol (3)当402NF3+3NiO = NO+NO2+3NiFz,A,G0= -438.7 kJ/mol, A,H0=-433.2 kJ/mol (4)-t-Co,O,wwwwwwFrom the above presented results, it is obvious that Al2O3010020000 600 700is an active reagent for NF3 decomposition at 400 °C, butTime on stream (min)not all of the 7-Al2O3 changed into AlF3 phase limited bythe mass transfer effect in the micropores [4]. In the fol-Figure 1. NF3 conversion over Al2O3, Fe2O3, Co3O4 and NiOr-Al.O3a)CEEO 3Fe,O,(b)730(2).2)(1)10 2(40 :701040 5(20/(° )▲Co,O,◆NiOs CoF,e)(d)(2)i10 20中国煤化工20/0° )YHCNMHGFigure 2. XRD patterns of (a) Al2O3, (b) Fe2O3, (C) Co3O4 and (d) NiO (1) before and (2) after reaction2(5(508(204(20/(6)20/(。)Journal of Natural Gas Chemistry VoL. 19 No.52010465givesand transition metal oxides coated Al2O3， it is clearspent reagents. As listed in Table 1, BET surface areas of thethat the reactivity of Al2O3 and the coated Al2O3spent de-fluorinated reagents were lower than those of the cor-increased in the order of Al2O3 <5%NiO/Al2O3