Nitrogen oxides (NOx) are emitted from various industrial processes and transportation activities, especially coal–fired power plants. The SCR catalysts that are most used are those in which WO3 is added to VOx/TiO2 (anatase). These vanadium-based catalysts exhibit an excellent efficiency in a temperature range from 300 to 400 °C . However, these vanadium-based catalysts also suffer from several drawbacks, including the harmful effects of vanadium on the environment, the high likelihood of SO2 oxidizing to o SO3, a narrow operation temperature window (300–400 °C), and the formation of N2O at high temperatures.

In particular, ceria is a potential substitute for vanadium due to its oxygen storage capacity and high redox ability when shifting between Ce4+ and Ce3+. Production of tungsten doped CeO2/TiO2 has been achieved with ammonium paratungstate for SCR of NOx, The Ce/Ti with 10 wt.% ceria (10Ce/Ti) exhibited excellent activity.

The preparation method of the SCR catalyst is as following steps: Cerium (III) nitrate [10 wt.% Ce; Ce(NO3)3·6H2O by using ceria (5, 10, 20, and 50 wt.% Ce) and anatase-type TiO2 powder (DT51) had been used as precursors. A calculated amount of TiO2 was gradually added to the ceria solution while stirring. The mixture was agitated in a slurry state for more than 1 h; then the moisture was removed at 70 °C using a rotary vacuum evaporator (Eyela Co., N–N series); and the mixture was dried overnight at 110 °C. Finally, the mixture was calcined in air for 5 h at 500 °C.

The 10Cesingle bondW/Ti catalyst was prepared according to the following process. Cerium nitrate (10 wt.% Ce) and ammonium paratungstate (10 wt.% WO3) were mixed in distilled H2O. The calculated amount of the TiO2 support was impregnated in this solution by stirring for 1 h, and then the moisture was removed at 70 °C using a rotary vacuum evaporator. The mixture was then dried overnight at 110 °C, and was subsequently calcined in air for 5 h at 500 °C. W/10Ce/Ti was prepared through impregnation of 10Ce/Ti and ammonium paratungstate using the method described above.

To sum up, tungsten doped CeO2/TiO2 has been produced with ammonium paratungstate for SCR of NOx, The Ce/Ti with 10 wt.% ceria (10Ce/Ti) exhibited excellent activity. Thus, various metals were added to the 10Ce/Ti. The tungsten-doped 10Ce/Ti catalyst exhibited the highest activity. The highest Ce3+ ratio was observed in 10Ce/W/Ti at 0.3027, and the catalyst efficiency had a positive correlation with higher Ce3+ ratios. The SCR activity was found to increase as the Ce3+ ratio increased when tungsten was added to 10Ce/W/Ti. Thus, the addition of tungsten to Ce/Ti resulted in excellent NOx conversion and SO2 resistance.

It is found that tantalum (Ta) and niobium (Nb) in concentrate of wolframite ((Fe,Mn)WO4) has been wasted: some of it goes to the insoluble residue after ammonium-leaching of the tungstic acid slurry; most of it goes to the solution of ammonium tungstate when (Fe,Mn)WO4 concentrate was digested by hydrochloric acid and the slurry of tungstic acid obtained was leached in ammonia. When the ammonium paratungstate (APT) was crystallized from the solution of ammonium tungstate, Ta and No were almost completely left in the mother liquor and their content reached up to 16 g/litre.

WO3 is a popular and least bothered an n-type semiconductor with promising electrochemical properties, a high surface area, a small pore-size distribution, with several exciting chemical and physical properties, which have made it a appropriate material for various applications such as catalysts, gas sensors, and energy storage applications. However, the conventional synthesis methods have the drawbacks of high cost, time consuming, and high environmental pollution.

Single-walled carbon nanotubes (SWCNTs) have been an area of intense research since their discovery in 1993, owing to their extraordinary mechanical and unique electronic properties. It has been applied in fields including field-emission, SPM tips, and sensors.  Catalyst is the decisive factor in fabrication of SWCNT by catalytic chemical vapor deposition (CCVD). The yield, purity, and textural properties of as-prepared SWCNTs were largely relied on the composition of the catalysts, the type of support material used, and the nature of the metal in the catalysts.