The Al2O3 and Mn/Al2O3 sorbents highly utilized in destructive sorption of NF3

Abstract

NF3 is commonly used as an etching and cleaning gas in semiconductor industry, however it is a strongly greenhouse gas. Therefore, the destruction of disposal NF3 is an urgent task to migrate the greenhouse effect. Among the technologies for NF3 abatement, the destructive sorption of NF3 over metal oxides sorbents is an effective way. Thus, the search for a highly reactive and utilized sorbent for NF3 destruction is in great demand. In this work, AlOOH supported on carbon-sphere (AlOOH/CS) as precursors were synthesized hydrothermally and heat-treated to prepare the Al2O3 sorbents. The influence of AlOOH/CS hydrothermal temperatures on the reactivity of derived Al2O3 sorbents for NF3 destruction was investigated, and it is shown that the Al2O3 from AlOOH/CS hydro-thermalized at 120 °C is superior to others. Subsequently, the optimized Al2O3 was covered by Mn(OH)x to prepare Mn/Al2O3 sorbents via changing hydrothermal temperatures and Mn loadings. The results show that the Mn/Al2O3 sorbents are more utilized than bare Al2O3 in NF3 destructive sorption due to the promotional effect of Mn2O3 as surface layer on the fluorination of Al2O3 as substrate, especially the optimal 5%Mn/Al2O3(160 °C) exhibits a utilization percentage as high as 90.4%, and remarkably exceeds all the sorbents reported so far. These findings are beneficial to develop more efficient sorbents for the destruction of NF3.

1. Introduction

Nitrogen tri-fluoride (NF3) is commonly used as an etching and cleaning gas in semiconductor industry. However, NF3 is a highly greenhouse gas with global warming potential of 17200 and atmospheric lifetime of 740 years [1], its emission can cause serious environmental pollution and climate problems. Therefore, it is of great significance to destruct the disposal NF3 before its emission into the atmosphere. As reported [2–4], catalytic hydrolysis is effective for NF3 destruction (2NF3 + 3H2O = NO + NO2 + 6HF), but the HF produced is severely corrosive to the reactors. In contrast, NF3 destructive sorption over metal oxides sorbents, such as 2NF3 + Al2O3 = NO + NO2 + 2AlF3, is a more factual method for its abatement without the formation of corrosive HF, furthermore the metal fluorides produced are valuable chemicals [5]. Thus, the search for a highly reactive and utilized sorbent for NF3 destruction is urgently demanded.

In our previous work, it is found that Al2O3 was an reactive sorbent for NF3 destruction in comparison with other single metal oxides such as Mn2O3, Fe2O3, Co3O4, NiO, however the utilization percentage of Al2O3 in NF3 reaction was as low as 53.1% [6,7]. How to improve the reactivity of Al2O3 in NF3 sorption? It is proposed to prepare the Al2O3 sorbent with larger surface area and pore volume using hydrothermal method rather than precipitation previously used in order to fasten the diffusion of NF3. Recently, we found that the Al2O3 covered by transition metal oxides such as V2O5, Fe2O3, Co3O4, NiO, especially Mn2O3, can be improved significantly for NF3 sorption. However, the utilization percentage of Mn2O3-coated Al2O3 (designated as Mn/Al2O3) sorbents prepared by the wetness impregnation of Mn(NO3)2 solution onto Al2O3 was less than 70%, and necessary to be improved [8,9]. In reference to the literatures of hydrothermal synthesis for porous oxides [10–19], we suggested to prepare the Mn2O3-coated Al2O3 sorbents by hydrothermal method instead of impregnation so as to enhance the interaction between Mn2O3 as surface layer and Al2O3 as substrate, and to deeply improve the reactivity for NF3 sorption.