Effect of the morphology of Ru/α-MnO2 on NH3-SCO performance

doi:10.11949/0438-1157.20230420

Abstract

Abstract:

α-MnO₂ with different morphology, such as wire (w), tube (t) and rod (r) were synthesized as supports to prepare Ru/α-MnO₂, and the effects of support morphology on the ammonia selective catalytic oxidation (NH₃-SCO) were investigated. Meanwhile, the physical and chemical properties, redox properties and acidity of the catalysts were characterized by various methods. The exposed facet was closely related to the morphology of α-MnO₂, for (110), (310) and (200) crystal planes were observed on the wire-, tube-, and rod-α-MnO₂, respectively. The introduction of Ru improves the water resistance of the catalyst, and the tubular Ru/α-MnO₂ has a NH₃ conversion rate of 86% and a N₂ selectivity of 98% under water vapor conditions. The effects of Ru on NH₃-SCO activity performance was closely related to its effect on the surface acidity and redox property of α-MnO₂. The addition of Ru reduced the surface acid amount of α-MnO₂-w and thus lowered its activity, while the improved reducibility of Ru to α-MnO₂-r compensated for the decreasing in the surface acid amount. However, for Ru/α-MnO₂-t, the simultaneous increase in reducibility and surface acid amount by the presence of Ru was the main reason for the enhancement in NH₃-SCO activity.

Key words: catalyst, support, oxidation, NH₃ selective catalytic oxidation, morphologies of α-MnO₂, acidity, redox

摘要：

以具有不同形貌的线状（w）、管状（t）和棒状（r）的α-MnO₂为载体制备了Ru/α-MnO₂催化剂，考察了载体形貌对于氨选择性催化氧化（NH₃-SCO）反应性能的影响，并利用多种手段表征了催化剂的物化性质、氧化还原性能和酸性。α-MnO₂形貌影响所暴露的晶面；线状、纳米棒和管状α-MnO₂分别暴露（110）、（310）和（200）晶面。Ru的引入提高了催化剂的耐水性能，其中管状Ru/α-MnO₂在水汽条件下NH₃转化率为86%，N₂的选择性为98%。Ru的引入对反应性能的影响与其对α-MnO₂表面酸性、氧化还原性能的影响密切相关。Ru降低了α-MnO₂-w表面酸量导致其活性下降；Ru对于α-MnO₂-r氧化性能的提高弥补了其导致的表面酸量的降低；而Ru对α-MnO₂-t氧化性和酸量的同时促进是Ru/α-MnO₂-t反应性能提升的主要原因。

关键词: 催化剂, 载体, 氧化, 氨选择性催化氧化, α-MnO₂形貌, 酸性, 氧化还原性

CLC Number:

TQ 137.1

Pan LI, Junyang MA, Zhihao CHEN, Li WANG, Yun GUO. Effect of the morphology of Ru/α-MnO₂ on NH₃-SCO performance[J]. CIESC Journal, 2023, 74(7): 2908-2918.

李盼, 马俊洋, 陈志豪, 王丽, 郭耘. Ru/α-MnO₂催化剂形貌对NH₃-SCO反应性能的影响[J]. 化工学报, 2023, 74(7): 2908-2918.

Figures/Tables 15

Fig.1 NH3-SCO activity and by-products of Ru/α-MnO2

Table 1 The textural properties of α-MnO2 and Ru/α-MnO2

催化剂	Ru负载量^①/%	比表面积^②/（m²/g）	反应速率^③/（10⁷ mol/(g·s)）	活化能^④/（kJ/mol）
α-MnO₂-w	—	139	3.7	31.3
Ru/α-MnO₂-w	1.84	133	2.4	45.9
α-MnO₂-t	—	26	2.6	43.4
Ru/α-MnO₂-t	1.79	24	3.2	35.7
α-MnO₂-r	—	70	1.5	46.6
Ru/α-MnO₂-r	1.90	65	2.7	42.8

Fig.2 Stability of Ru/α-MnO2 with the presence of water

Fig.3 XRD patterns of α-MnO2 and Ru/α-MnO2

Fig.4 SEM,TEM and HR-TEM images of α-MnO2

Fig.5 SEM，TEM and HR-TEM images of Ru/α-MnO2

Fig.6 EDX-mapping of Ru/α-MnO2

Fig.7 Raman spectra of Ru/α-MnO2

Fig.8 Mn 2p3/2 XPS spectra of α-MnO2 and Ru/α-MnO2

Table 2 XPS data， H2 consumption and relative acidity of α-MnO2 and Ru/α-MnO2

催化剂	Ru⁴⁺/Ru^①	Mn³⁺/Mn^4+①	O_β/O_α^①	表面平均氧化态^②	实际耗氢量^③/(mmol/g)	相对酸浓度^④
α-MnO₂-w	—	1.93	0.24	3.51	8.57	2.9
Ru/α-MnO₂-w	0.64	1.81	0.21	3.35	8.51	0.1
α-MnO₂-t	—	1.78	0.22	3.68	9.77	0.4
Ru/α-MnO₂-t	0.65	1.86	0.24	3.33	9.83	1
α-MnO₂-r	—	1.71	0.20	3.72	9.83	2.2
Ru/α-MnO₂-r	0.61	1.83	0.23	3.58	10.41	0.9

Fig.9 O 1s XPS spectra of α-MnO2 and Ru/α-MnO2

Fig.10 Ru 3p XPS spectra of Ru/α-MnO2

Fig.11 H2-TPR profiles of α-MnO2 and Ru/α-MnO2

Fig.12 NH3-TPD profiles of α-MnO2 and Ru/α-MnO2

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Effect of the morphology of Ru/α-MnO₂ on NH₃-SCO performance

Ru/α-MnO₂催化剂形貌对NH₃-SCO反应性能的影响

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