A solid ternary mixture consisting of NaF, silicon and one of the metal oxides such as AI2O3, MgO, CaO, SrO, BaO was prepared and used as a defluorinated reagent for CF4 decomposition. The results show that the initial conversion of CF4 reached 100% over NaF-Si-MgO and NaF-Si-CaO at 850 °C, and the reagent with NaF/Si/MgO molar ratio of 33/34/33 exhibited a high reactivity with a full conversion of CF4 lasting for 57 min. The plausible paths of CF4 decomposition over NaF-Si-Al203, NaF-Si-MgO, NaF-Si-CaO, NaF-Si-SrO and NaF-Si-BaO are proposed.

NF3 decomposition over transition metal oxides coated MgO reagents in the absence of water is investigated. The results show that NF3 can be decomposed completely over pure MgO but the time of NF3 steady full conversion kept as short as 80 min, while the reactivities of coated MgO reagents were remarkably enhanced by transition metal oxides, for example the time of NF3 complete conversion over 12%Fe/MgO extended to 380 min. It is suggested that not only an increase in surface area but also a significant enhancement in the fluorination of MgO substrate caused by the surface transition metal oxides result in an improved reactivity of coated MgO reagents for NI3 decomposition.

NF3 decomposition in the absence of water over Al2O3, Fe2O3, Co3O4 and NiO, and transition metal oxides (Fe2O3, Co3O4 and NiO) coated Al2O3 reagents was investigated. The results show that Al2O3 is an active reagent for NF3 decomposition with 100% conversion lasting for 8.5 h at 400 °C. Fe2O3, Co3O4 and NiO coated Al2O3 reagents are superior to bare Al2O3, and 5%Co3O4/Al2O3 has a high reactivity with NF3 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 fluorination of Al2O3.

Au/Co3O4 catalysts with different gold loadings were prepared by the deposition-precipitation method using HAuCl4 solution through adjustment of the pH value to 7, 9 or 11. Their catalytic properties for N2O decomposition in the presence of oxygen were investigated. 0.29%Au/Co3O4 catalyst prepared at the pH value of 9 exhibited higher catalytic activity than 0.31%Au/ZnCo2O4 prepared under optimal conditions although ZnCo2O4 was more active than Co3O4. AES, BET, XRD, SEM, XPS and H2-TPR characterization results indicated a synergistic effect existed between gold and cobalt species in Au/Co3O4, which is, however, absent in the Au/ZnCo2O4. Despite that N2O was completely decomposed at 500?C in oxygen atmosphere for both the samples, the N2O conversion was decreased to 92% and 63% after the reaction was carried out for 10 h in the presence of both oxygen and steam over the 0.29%Au/Co3O4 and the 0.31%Au/ZnCo2O4, respectively.

Au/Co-Al catalysts were prepared by using the ion-exchange and coprecipitation methods, and their activities for the catalytic decomposition of N2O were tested. BET, XRD, and H2-TPR techniques were used to characterize the catalysts. The results show that the activity of Au/Co-Al catalyst prepared by using ion-exchange method is higher than that using coprecipitation method. For the catalysts prepared by ion-exchange method, the effects of preparation parameters, such as Au loading, pretreatment of HAuCl4 solution, and calcination temperature, upon N2O conversion were investigated. The optimal preparation parameters of Au/Co-Al catalysts are 1.1% of Au loading, HAuCl4 solution adjusted to pH 9, and 300°C of calcination temperature. It is indicated that the addition of Na species in Co-Al mixed oxide promoted the reduction of Co3+ to Co2+ and enhanced the catalytic activity for N2O decomposition.

Three CuAl hydrotalcite-like compounds (CuAl-HLc) with Cu/Al atomic ratio of 2.0, 3.1 and 4.1 were prepared by a co-precipitation method and calcined to convert into CuAl mixed oxides. The CuAl mixed oxide with Cu/Al atomic ratio of 3.1 was incipiently impregnated by alkali metal (Na, K, Cs) salt solution to prepare the modified CuAl mixed oxide catalysts. The properties of the catalysts were characterized by AES, XRD, FT-IR, BET, H2-TPR and XPS techniques. The effect of CuAl mixed oxide compositions, alkali metal types and potassium precursors on catalytic activity for N2O decomposition in the presence of oxygen were investigated. It is revealed that the catalytic activity of CuAl mixed oxides impregnated by K2CO3 solution is higher than that of Na2CO3 and Cs2CO3 doped catalysts. In addition, the catalytic activity of CuAl mixed oxides can be largely enhanced by the addition of K species from the precursors of K2CO3 and K2C2O4, whereas KNO3- and CH3COOK-doped catalysts show a lower activity than sole CuAl oxide. The optimal K-doped catalyst exhibits a good activity for N2O decomposition in the presence of oxygen and steam.

A solid ternary mixture consisting of NaF, silicon and one metal oxide such as La2O3, CeO2, Pr6O11, Nd2O3, and Y2O3 was prepared and used as de-fluorinated reagent for CF4 decomposition. The results show that 90% conversion of CF4 can be reached initially over NaF-Si-La2O3, NaF-Si-CeO2, NaF-Si-Nd2O3, and NaF-Si-Y2O3 at 850 °C. The fresh and used reagents were characterized using XRD and XPS techniques. It was found that the active components of NaF and metal oxides in NaF-Si-CeO2, NaF-Si-Pr6O11, NaF-Si-Nd2O3, and NaF-Si-Y2O3 were transformed into inert phases of mixed metal fluorides and silicates, respectively, resulting in an ineffective utilization of these de-fluorinated reagents, whereas no inert phases from NaF and La2O3 can be observed in the used NaF-Si-La2O3, indicating the NaF-Si-La2O3 reagent could be utilized more efficiently than the other reagents in CF4 decomposition.

Zn-Fe spinel oxides were prepared by co-precipitation method and used as the catalysts in N2O decomposition in the presence of oxygen; the effects of spinel oxide composition, calcination temperature, and K doping on their catalytic activity were investigated. In addition, the Zn-Fe spinel oxides were characterized by N2 physisorption, X-ray diffraction and H2-TPR techniques. The results indicated that the Zn-Fe spinel oxides are active in N2O decomposition in the presence of oxygen; over the Zn0.8Fe0.2Fe2O4-400 catalyst with the optimized composition and calcined at 400°C, the conversions of N2O in the absence and in the presence of steam achieve 63.5% and 22.2%, respectively, after reaction at 500°C for 10 h, which are much higher than those over Fe3O4. However, the K-doped Zn-Fe spinel oxides exhibited lower activity than the bare Zn-Fe oxide, as K doping may lead to a substantial decrease of surface area and the migration of potassium crystallites to FeOx surface that will inhibit the ferric species from reduction and active oxygen species from removal from the catalyst surface.

NiAl mixed oxides with Ni/Al atomic ratio of 2.0, 2.7 and 4.1 were prepared by calcining the corresponding NiAl hydrotalcite-like compounds (NiAl-HLc), and applied in N2O decomposition. The NiAl mixed oxide with Ni/Al atomic ratio of 2.7 was incipiently impregnated by alkali metal (Na, K, Cs) carbonate solution to prepare the promoted NiAl mixed oxide catalysts. The catalysts were characterized by XRD, ICP-AES, FTIR, BET, H2-TPR and XPS techniques, and their catalytic activities for N2O decomposition were tested. The effect of NiAl mixed oxides composition, alkali metal species, and potassium precursors on catalytic activity was investigated. The results show that the catalytic activity of NiAl mixed oxide impregnated by K2CO3 solution is much higher than Na2CO3 and Cs2CO3 modified catalysts; the catalytic activity of NiAl mixed oxides is largely enhanced by the addition of K species from the precursors of K2CO3, K2C2O4 and CH3COOK.

Several Al2O3 samples were prepared by a precipitation method coupled with ultrasonic treatment, and NF3 decomposition without water over Al2O3 reagents is carried out. The effect of preparation parameters of Al2O3 reagents, such as precipitating agents, structure directing agents, and calcining temperatures on their reactivity for NF3 decomposition has been investigated. The results show that NF3 can be decomposed completely at 400 °C, and full conversion of NF3 maintains 580 min over the best Al2O3 reagent, calcined at 600 °C which was prepared using both PEG-2000 and Tween-60 as structure directing agents, ammonia as a precipitating agent.

NixCo1–xCoAlO4 spinel oxides with different compositions were prepared by sol-gel method and further modified with K2CO3 by incipient impregnation. The NixCo1–xCoAlO4 spinel oxides were characterized by means of nitrogen physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed reduction by hydrogen (H2-TPR); the effect of preparation parameters such as composition, mother liquid pH value, and potassium loading on their catalytic activity in N2O decomposition was investigated. The results show that the K/Ni0.15Co0.85CoAlO4 catalyst prepared with a pH value of 3 and a K/(Ni+Co) molar ratio of 0.1 is most active for N2O decomposition; over it, N2O can be completely decomposed into nitrogen and oxygen at 450°C in the presence of oxygen. K-modified catalysts exhibit high catalytic activity, good reducibility and resistance towards water, as K species may be able to weaken the surface metal-oxygen bonds.

NiAl mixed oxides derived from hydrotalcite-like compounds (HLCs) with Ni/Al molar ratio of 4.1 were incipiently impregnated by potassium carbonate solution to prepare K-promoted NiAl mixed oxide catalysts with K/Ni molar ratio in the range of 0.05 to 0.2, and applied in catalytic decomposition of N2O. The catalysts were characterized by ICP-AES, XRD, BET, H2-TPR, XPS techniques, and their catalytic activities for N2O decomposition were tested. The results show that the catalytic activity of NiAl mixed oxide impregnated by K2CO3 solution is much higher than that of NiAl mixed oxide without K species and superior to the catalyst prepared by fresh NiAl-HLC impregnated using K2CO3 solution. The effect of K loadings and calcination temperatures of catalysts on catalytic activity has been investigated. It is found that the catalytic activity of NiAl mixed oxide, especially the one with K/Ni=0.1 and calcinated at 400°C, is largely enhanced by the addition of K species in the presence of oxygen and/or steam. XPS and H2-TPR results show that the electron binding energy of surface active NiO species in K-promoted NiAl mixed oxides shifts to lower value, and the surface Ni-O bond is weakened, thus the reduction peak of surface NiO moves to lower temperature, and the catalytic activity is improved.

Mg-Co and Mg-Mn-Co composite oxides with different compositions were prepared by sol-gel method for N2O catalytic decomposition in the presence of oxygen. Of Mg-Mn-Co catalysts, the one with higher activity was impregnated by K2CO3 solution to make K-modified catalyst. These catalysts were characterized by X-ray diffraction (XRD), nitrogen physisorption (BET), scanning electron microscopy (SEM), temperature-programmed reduction of hydrogen (H2-TPR), and temperature-programmed desorption of oxygen (O2-TPD). The effect of preparation parameters such as compositions and potassium loadings on their catalytic activity has been investigated. The results show that K-modified catalysts exhibit better activity and higher resistance towards water in contrast to un-modified catalyst due to the weakness of surface metal-oxygen bonds. Among these catalysts, 0.02K/MgMn0.2Co1.8O4 is the most active, over which 97% and 60% conversions of N2O can be reached at 400°C after continuous running for 50 h under the atmosphere of oxygen-alone and oxygen-steam together, respectively. When the steam is switched off, the catalytic activity of 0.02K/MgMn0.2Co1.8O4 can be restored to large extent, indicating the good water-resistance of K-modified catalyst.

A series of MgxFe1–xFe2O4 spinel oxides were prepared and characterized by means of nitrogen physisorption, X-ray diffraction (XRD) and temperature-programmed reduction of hydrogen (H2-TPR). The effect of composition, calcination temperature, and potassium doping on the catalytic activity of the Mg-Fe mixed oxides in N2O decomposition was investigated. The results indicated that the Mg0.6Fe0.4Fe2O4 catalyst calcined at 500°C exhibits highest activity in N2O decomposition. Unexpectedly, the catalyst activity is depressed by the addition of potassium, as the potassium doping may inhibit the reduction of surface iron oxides and reduce the surface area of K-modified catalysts. Long-term tests at 500°C for 10 h also illustrate that Mg0.6Fe0.4Fe2O4 is superior to FeOx catalyst either in the oxygen-alone or in the oxygen-steam concomitant atmosphere.