MoO x 状态调控及其对VO x /MoO x ⁃TiO2催化剂脱硝性能和热稳定性的影响

doi:10.12422/j.issn.1006-396X.2024.04.006

摘要/Abstract

摘要：

将七钼酸铵分别用水和草酸溶液溶解后与TiO₂复合制备MoO _x ?TiO₂载体，通过浸渍法负载钒获得VO _x /MoO _x ?TiO₂催化剂；采用XRD、SEM、BET、XPS、H₂?TPR和NH₃?TPD表征手段研究催化剂的结构和性质，并考察了其脱硝活性和高温老化性能。结果表明，草酸助溶七钼酸铵制得的VMoTiO?F在210~510 ℃的脱硝效率大于80.0%，优于用水溶解制备的VMoTiH?F；VMoTiO?F表面存在较多的MoO _x，可增强与VO _x 的相互作用，促进催化剂表面产生更多的低价态VO _x 和表面化学吸附氧(O_α)活性物种；VMoTiO?F中的VO _x 和MoO _x 相互作用还能提高低温氧化还原性能，有利于催化过程中的电子传递；VMoTiH?F相比VMoTiO?F有更多的MoO _x 进入TiO₂晶格，提高TiO₂的热稳定性，而VMoTiO?A中的锐钛矿TiO₂在高温老化中被严重烧结甚至部分转变为惰性金红石晶型，导致表面酸性位损失和氧化还原性能降低，因此VMoTiH?A催化剂的脱硝性能明显优于VMoTiO?A。

关键词: VO _x /MoO _x ?TiO₂, 氨选择性催化还原, MoO _x ?TiO₂复合载体, 活性VO _x, 热稳定性

Abstract:

Ammonium heptamolybdate was dissolved in water or oxalic acid solution,and then compounded with TiO₂ to prepare MoO _x ?TiO₂ support,and the VO _x /MoO _x ?TiO₂ catalysts were obtained after loading vanadium by impregnation method.The structure and properties of the catalysts were characterized by XRD,SEM,BET,XPS,H₂?TPR and NH₃?TPD,and its denitration activity and high temperature aging performance were investigated.The results showed that the denitrification efficiency of VMoTiO?F prepared by oxalic acid?assisted dissolution of (NH₄)₆Mo₇O₂₄ was greater than 80.0% at 210 ~ 510 °C,which was better than that of VMoTiH?F prepared by water dissolution.Because there was more MoO _x on the surface of VMoTiO?F,the interaction with VO _x was enhanced,which promoted the production of more low?valence VO _x and surface chemisorbed oxygen (O_α) active species on the surface of the catalyst.At the same time,the interaction between VO _x and MoO _x could also improve the low?temperature redox performance and facilitate the electron transfer in the catalytic process.After high temperature aging,VMoTiH?F had more MoO _x into the TiO₂ lattice than VMoTiO?F,which was helpful to improve the thermal stability of TiO₂.However, anatase TiO₂ in VMoTiO?A was seriously sintered or even partially transformed into inert rutile crystal during high temperature aging,resulting in the loss of surface acid sites and the reduction of redox properties.Therefore,the denitrification performance of VMoTiH?A catalyst was significantly higher than that of VMoTiO?A.

Key words: VO _x /MoO _x ?TiO₂, NH₃?SCR, MoO _x ?TiO₂ composite support, Active component VO _x, Thermal stability

中图分类号:

TQ032.4

方萍, 陈康欣, 林雨婷, 范楷浩, 单承宇, 刘雪松. MoO _x 状态调控及其对VO _x /MoO _x ⁃TiO₂催化剂脱硝性能和热稳定性的影响[J]. 石油化工高等学校学报, 2024, 37(4): 40-48.

Ping FANG, Kangxin CHEN, Yuting LIN, Kaihao FAN, Chengyu SHAN, Xuesong LIU. The Regulation of MoO _x State and Its Effect on the Denitration Performance and Thermal Stability of VO _x /MoO _x ⁃TiO₂ Catalysts[J]. Journal of Petrochemical Universities, 2024, 37(4): 40-48.

图/表 11

图1 催化剂的NH3?SCR活性图

Fig.1 NH3?SCR activity diagram of catalysts

图2 催化剂的XRD图谱

Fig.2 XRD patterns of the catalysts

表1 催化剂的物相组成、晶粒尺寸、晶胞体积和比表面积

Table 1 Phase composition,particle size,cell volume and SBET of the catalyst

催化剂	w/%		晶粒尺寸^*/nm		晶胞体积/ nm³	粒径分布范围^**/nm	S_BET /（m² $⋅$ g^-1）
催化剂	锐钛矿型TiO₂	金红石TiO₂	锐钛矿TiO₂	金红石TiO₂	晶胞体积/ nm³	粒径分布范围^**/nm	S_BET /（m² $⋅$ g^-1）
VMoTiH⁃F	100.0	-	17.5	-	0.135 67	10~30	67.49
VMoTiO⁃F	100.0	-	26.4	-	0.136 17	20~45	49.32
VMoTiH⁃A	100.0	-	31.9	-	0.135 85	26~60	44.15
VMoTiO⁃A	95.0	5.0	103.1	160.4	0.136 12	80~170	10.25

表1 催化剂的物相组成、晶粒尺寸、晶胞体积和比表面积

Table 1 Phase composition,particle size,cell volume and SBET of the catalyst

催化剂	w/%		晶粒尺寸^*/nm		晶胞体积/ nm³	粒径分布范围^**/nm	S_BET /（m² $⋅$ g^-1）
催化剂	锐钛矿型TiO₂	金红石TiO₂	锐钛矿TiO₂	金红石TiO₂	晶胞体积/ nm³	粒径分布范围^**/nm	S_BET /（m² $⋅$ g^-1）
VMoTiH⁃F	100.0	-	17.5	-	0.135 67	10~30	67.49
VMoTiO⁃F	100.0	-	26.4	-	0.136 17	20~45	49.32
VMoTiH⁃A	100.0	-	31.9	-	0.135 85	26~60	44.15
VMoTiO⁃A	95.0	5.0	103.1	160.4	0.136 12	80~170	10.25

图3 催化剂的SEM图

Fig.3 SEM images of the catalysts

图4 催化剂的吸附?脱附和孔径分布曲线

Fig.4 The adsorption and desorption curves and pore size distribution of the catalysts

图5 催化剂的XPS谱图

Fig.5 XPS spectra of the catalysts

表2 催化剂表面各元素的相对浓度及不同价态原子浓度占比

Table 2 The relative concentration of each element on the catalyst surface and the proportion of atomic concentration of different valence states

催化剂	A(V³⁺+V⁴⁺)/ A(V_总)	A（Mo⁵⁺）/ A(Mo⁵⁺+Mo⁶⁺)	A（O_α）/A（O $α,$ +O_α+O_β）	A（V）/A（Ti）	A（Mo）/A（Ti）
VMoTiH⁃F	0.615 7	0.197 1	0.229 9	0.074 2	0.052 1
VMoTiO⁃F	0.796 3	0.142 7	0.323 3	0.064 6	0.062 5
VMoTiH⁃A	0.584 8	0.284 0	0.222 4	0.059 9	0.075 5
VMoTiO⁃A	0.466 6	0.325 8	0.175 7	0.014 0	0.015 0

表2 催化剂表面各元素的相对浓度及不同价态原子浓度占比

Table 2 The relative concentration of each element on the catalyst surface and the proportion of atomic concentration of different valence states

催化剂	A(V³⁺+V⁴⁺)/ A(V_总)	A（Mo⁵⁺）/ A(Mo⁵⁺+Mo⁶⁺)	A（O_α）/A（O $α,$ +O_α+O_β）	A（V）/A（Ti）	A（Mo）/A（Ti）
VMoTiH⁃F	0.615 7	0.197 1	0.229 9	0.074 2	0.052 1
VMoTiO⁃F	0.796 3	0.142 7	0.323 3	0.064 6	0.062 5
VMoTiH⁃A	0.584 8	0.284 0	0.222 4	0.059 9	0.075 5
VMoTiO⁃A	0.466 6	0.325 8	0.175 7	0.014 0	0.015 0

图6 催化剂的H2?TPR图谱

Fig.6 The H2?TPR profiles of the catalysts

表3 由H2?TPR结果计算得出的H2消耗量

Table 3 Amounts of H2 consumption from the H2?TPR results

催化剂	还原峰温度/°C			H₂消耗量/（μmol $⋅$ g^-1）			H₂总消耗量/ （μmol $⋅$ g^-1）
催化剂	低温峰	中温峰	高温峰	低温峰	中温峰	高温峰	H₂总消耗量/ （μmol $⋅$ g^-1）
VMoTiH⁃F	542/587	—	813	353.5/297.6	—	2.9	654.0
VMoTiO⁃F	503/564	633	790	84.4/371.7	66.6	47.9	570.6
VMoTiH⁃A	546/596	—	—	101.9/141.4	—	—	243.3
VMoTiO⁃A	585	660	—	44.6	118.0	—	162.6

表3 由H2?TPR结果计算得出的H2消耗量

Table 3 Amounts of H2 consumption from the H2?TPR results

催化剂	还原峰温度/°C			H₂消耗量/（μmol $⋅$ g^-1）			H₂总消耗量/ （μmol $⋅$ g^-1）
催化剂	低温峰	中温峰	高温峰	低温峰	中温峰	高温峰	H₂总消耗量/ （μmol $⋅$ g^-1）
VMoTiH⁃F	542/587	—	813	353.5/297.6	—	2.9	654.0
VMoTiO⁃F	503/564	633	790	84.4/371.7	66.6	47.9	570.6
VMoTiH⁃A	546/596	—	—	101.9/141.4	—	—	243.3
VMoTiO⁃A	585	660	—	44.6	118.0	—	162.6

图7 催化剂的NH3?TPD谱图

Fig.7 NH3?TPD profiles of the catalysts

表4 由NH3?TPD结果计算的NH3脱附量

Table 4 The NH3 desorption calculated from the NH3?TPD results

催化剂	还原峰温度/°C			NH₃脱附量/（μmol·g^-1）			NH₃脱附总量/ （μmol·g^-1）
催化剂	低温峰	中温峰	高温峰	低温峰	中温峰	高温峰	NH₃脱附总量/ （μmol·g^-1）
VMoTiH⁃F	133	221	356	22.99	67.57	45.20	135.76
VMoTiO⁃F	121	195	338	15.52	49.89	30.38	95.79
VMoTiH⁃A	101	156	232	8.91	15.48	17.71	42.10
VMoTiO⁃A	121	195	—	4.17	12.32	—	16.49

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MoO _x 状态调控及其对VO _x /MoO _x ⁃TiO₂催化剂脱硝性能和热稳定性的影响

The Regulation of MoO _x State and Its Effect on the Denitration Performance and Thermal Stability of VO _x /MoO _x ⁃TiO₂ Catalysts

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