Wei Li,Rui-tang Guo,Shu-xian Wang,Wei-guo Pan,Qi-lin Chen,Ming-yuan Li,Peng Sun,Shu-ming Liu
Heavy metals (such as Zn and Pb) have a deactivation effect on the catalyst for selective catalytic reduction of NO with NH 3 . In this study, it was found that the modification of Mn/TiO 2 catalyst by Nb could greatly enhance its Zn resistance. From the characterization results of BET, XRD, H 2 -TPR, NH 3 -TPD, it may be concluded that the introduction of Nb into Mn/TiO 2 catalyst would lead to its lower crystallinity , more acid sites and higher concentrations of Mn 4 + and surface chemisorbed oxygen. The results of in situ DRIFT study reveal that the NH 3 -SCR reactions over Mn/TiO 2 and Mn-Nb/TiO 2 all obey both the Langmuir-Hinshelwood mechanism and the Eley–Rideal mechanism, and the doping of Nb on Mn/TiO 2 catalyst could promote the adsorption of NH 3 and NOx species on it. All these features make a contribution to the high SCR activity and good Zn resistance of Mn-Nb/TiO 2 catalyst.
Fufeng Cai,Peijing Lu,Jessica Juweriah Ibrahim,Yu Fu,Jun Zhang,Yuhan Sun
Methanol steam reforming is regarded as a very promising process to generate H 2 suitable for fuel cells. Typically, the Pd-based catalysts can catalyze efficiently methanol steam reforming for hydrogen production . But their high selectivity to CO, a byproduct of methanol reforming reaction , severely limits their potential application. In this work, a series of Nb-modified Pd−Zr−Zn catalysts with different Nb loadings were prepared to study their catalytic activities with more focus on the role of Nb on Pd−Zr−Zn catalyst for methanol steam reforming. The prepared catalysts were fully analyzed by using various characterization techniques, for example, ICP , BET, SEM, XRD , H 2 -TPR, NH 3 -TPD, HRTEM , CO chemisorption , XPS, and Raman. The experimental results showed that an increase in Nb loading for the Nb-modified Pd−Zr−Zn catalysts led to a decrease of the methanol conversion and H 2 production rate. This was probably due to the decrease in the amount of oxygen vacancies on the catalyst surface . However, introduction of Nb into Pd−Zr−Zn catalyst increased the acid strength on the catalytic surface. The aldehyde species derived from methanol decomposition were readily transformed to HCOOH, thus yielding high selectivity to CO 2 for the Nb-modified Pd−Zr−Zn catalysts. Significantly, the addition of Nb to Pd−Zr−Zn catalyst facilitated the incorporation of Pd into the ZnO lattices, which led to the formation of Pd−Zn alloy. Consequently, the Nb-modified Pd−Zr−Zn catalysts exhibited significantly lower CO selectivity and production rate than the Pd−Zr−Zn catalyst. From the results, this work offers a new way to the rational design of selective methanol steam reforming catalysts to decrease the formation of byproduct CO.
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