S、P、Si掺杂对钒钛催化剂活性物种状态调控及脱硝性能影响

doi:10.3969/j.issn.1006-396X.2021.05.003

摘要/Abstract

摘要：

依次采用溶胶?凝胶法和浸渍法制备了一系列S、P、Si掺杂的TiO₂载体和相应的VO_x/TiO₂催化剂，以提高催化剂的SCR性能。其中，S掺杂的VO_x/TiO₂催化剂具有最佳的中低温SCR性能和最宽的工作温度窗口。根据各种表征分析结果可知，掺杂元素通过促进VO_x团聚生成具有较高的SCR反应活性的聚合态VO_x；而S⁴⁺和Si⁴⁺取代TiO₂中的Ti⁴⁺生成了Ti-O-S和Ti-O-Si键，这使催化剂中产生了更多的低价态V(V⁴⁺+V³⁺)和表面化学吸附氧。两者协同作用可促进NO氧化生成NO₂，产生的NO₂可通过加速VO_x物种在Redox过程中的重氧化来参与快速SCR反应，进而提升VO_x/TiO₂催化剂的中低温脱硝性能。由于P掺杂的VO_x/TiO₂催化剂中产生了较多的磷酸盐，从而导致其氧化还原性能和中低温活性相对较低。S、P、Si掺杂虽然对催化剂的酸性性能产生了显著的影响，但这并不是影响催化剂SCR活性的决定性因素。

关键词: 掺杂, VO_x/TiO₂催化剂, 钒物种, 活性氧物种, NH₃?SCR

Abstract:

A series of S, P, Si?doped TiO₂ supports and the corresponding VO_x/TiO₂ catalysts were prepared by sol?gel method and impregnation method for the purpose of enhancing SCR performance.Among them,the S?doped VO_x/TiO₂ catalyst exhibited the best low and medium temperature SCR performance and the widest active temperature window.According to the results of various analyses,the doping greatly influenced the agglomeration of vanadium species.As a result, numerous active polymeric VO_xspecies were emerged on the surface of catalysts.Meanwhile,S and Si was doped into TiO₂ lattice via the replacement of Ti⁴⁺ by S⁴⁺ and Si⁴⁺ to generate Ti-O-S and Ti-O-Si bonds,along with producing more surface V⁴⁺+V³⁺ and more chemisorbed oxygen species.The synergistic effect of the two active species can promote the oxidation of NO to NO₂,which can participate in the fast?SCR reaction by accelerating the reoxidation of VO_x species in the Redox process,and then improve the SCR performance of VO_x/TiO₂ catalyst at low and medium temperature range.The redox ability and activity of P?doped VO_x/TiO₂ catalyst are relatively low,because more phosphate is produced in the catalyst.Although doping S,P and Si has a significant effect on the acidity of the catalyst,it is not the dominate factor to determine the SCR activity.

Key words: Doping, VO_x/TiO₂ catalyst, Vanadium species, Active oxygen species, NH₃?SCR

中图分类号:

O643.32

赵博, 随志明, 李浙飞, 霍婉莹, 王阔, 沈刚峰, 刘雪松. S、P、Si掺杂对钒钛催化剂活性物种状态调控及脱硝性能影响[J]. 石油化工高等学校学报, 2021, 34(5): 16-23.

Bo Zhao, Zhiming Sui, Zhefei Li, Wanying Huo, Kuo Wang, Gangfeng Shen, Xuesong Liu. Effects of S, P, Si Doping on the Evolution of Active Species and NH₃⁃SCR Activity of a VO_x/TiO₂ Catalyst[J]. Journal of Petrochemical Universities, 2021, 34(5): 16-23.

图/表 11

图1 各种VOx/TiO2催化剂的脱硝效率、 N2选择性、NO氧化性能

Fig. 1 NOx conversion and N2 selectivity and NO oxidation curves of the VOx/TiO2 catalysts

图2 催化剂和载体的XRD谱图

Fig. 2 XRD patterns of the supports and catalysts

表1 载体及催化剂的晶粒尺寸、比表面积、平均孔径和孔容

Table 1 Crystallite size, SBET, average pore diameter and pore volume of the supports and catalysts

载体及催化剂	晶粒尺寸/nm	晶胞体积/nm³	比表面积/（ $m 2$ $⋅$ g^-1）	平均孔径/nm	孔容/（ $c m 3$ ·g^-1）
V/Ti	21.4	0.136 1	39.08	21.2	0.17
V/Ti⁃S	18.8	0.135 6	44.92	24.5	0.24
V/Ti⁃P	14.2	0.135 8	78.88	14.1	0.27
V/Ti⁃Si	20.1	0.135 7	59.14	17.9	0.25
TiO₂	19.9	0.136 2	41.33	19.6	0.18
TiO₂⁃S	18.4	0.135 7	54.03	18.1	0.26
TiO₂⁃P	13.6	0.135 9	93.48	12.8	0.30
TiO₂⁃Si	16.5	0.135 8	59.33	17.4	0.25

表1 载体及催化剂的晶粒尺寸、比表面积、平均孔径和孔容

Table 1 Crystallite size, SBET, average pore diameter and pore volume of the supports and catalysts

载体及催化剂	晶粒尺寸/nm	晶胞体积/nm³	比表面积/（ $m 2$ $⋅$ g^-1）	平均孔径/nm	孔容/（ $c m 3$ ·g^-1）
V/Ti	21.4	0.136 1	39.08	21.2	0.17
V/Ti⁃S	18.8	0.135 6	44.92	24.5	0.24
V/Ti⁃P	14.2	0.135 8	78.88	14.1	0.27
V/Ti⁃Si	20.1	0.135 7	59.14	17.9	0.25
TiO₂	19.9	0.136 2	41.33	19.6	0.18
TiO₂⁃S	18.4	0.135 7	54.03	18.1	0.26
TiO₂⁃P	13.6	0.135 9	93.48	12.8	0.30
TiO₂⁃Si	16.5	0.135 8	59.33	17.4	0.25

图3 催化剂的TEM

Fig.3 SEM images of catalysts

图4 催化剂的V 2p , Ti 2p , O 1s 、S 2p XPS谱图

Fig. 4 XPS spectra of catalysts: V 2p, Ti 2p , O 1s and S 2p

表2 不同方法所得表面原子浓度比

Table 2 Atomic ratios obtained by different characterization methods

催化剂	表面原子浓度比/%
催化剂	（V/Ti）^a	（V/Ti）^b	（Ad/Ti）^a	（Ad/Ti）^b
V/Ti	0.040	0.009	-	-
V/Ti⁃S	0.032	0.009	0.070	0.008
V/Ti⁃P	0.021	0.009	0.081	0.008
V/Ti⁃Si	0.033	0.009	0.074	0.008

图5 催化剂在925~1 090 cm-1的Raman光谱

Fig. 5 Raman spectra of the catalysts in the ranges of 925~1 090 cm-1

图6 催化剂的H2?TPR曲线

Fig. 6 H2?TPR profiles of the catalysts

图7 催化剂的NH3?TPD曲线

Fig. 7 NH3?TPD profiles of the catalysts

表3 根据H2?TPR和NH3?TPD结果计算得出的H2消耗量和NH3脱附量

Table 3 Amounts of H2 consumption and NH3?TPD on the catalysts from the H2?TPR and NH3?TPD curves

催化剂	H₂消耗量/（μmol $⋅$ g^-1）				NH₃脱附量/（μmol $⋅$ g^-1）
催化剂	低温峰	中温峰	高温峰	总量	低温峰	中温峰	高温峰	总量
V/Ti	201	-	-	201	6.11	20.37	26.22	52.70
V/Ti⁃S	242	257	97	596	7.76	28.11	28.46	64.33
V/Ti⁃P	359	103	167	629	26.69	28.55	21.58	76.82
V/Ti⁃Si	212	-	-	212	6.94	8.64	25.68	41.26

表3 根据H2?TPR和NH3?TPD结果计算得出的H2消耗量和NH3脱附量

Table 3 Amounts of H2 consumption and NH3?TPD on the catalysts from the H2?TPR and NH3?TPD curves

催化剂	H₂消耗量/（μmol $⋅$ g^-1）				NH₃脱附量/（μmol $⋅$ g^-1）
催化剂	低温峰	中温峰	高温峰	总量	低温峰	中温峰	高温峰	总量
V/Ti	201	-	-	201	6.11	20.37	26.22	52.70
V/Ti⁃S	242	257	97	596	7.76	28.11	28.46	64.33
V/Ti⁃P	359	103	167	629	26.69	28.55	21.58	76.82
V/Ti⁃Si	212	-	-	212	6.94	8.64	25.68	41.26

图8 S、P、Si掺杂改善V/Ti中低温SCR活性的作用机理

Fig. 8 Mechanism of S, P and Si doping to improve SCR activity in V/Ti catalyst at low temperature

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