ترجمه مقاله نقش ضروری ارتباطات 6G با چشم انداز صنعت 4.0
- مبلغ: ۸۶,۰۰۰ تومان
ترجمه مقاله پایداری توسعه شهری، تعدیل ساختار صنعتی و کارایی کاربری زمین
- مبلغ: ۹۱,۰۰۰ تومان
SUZ-4-based Pt-Sn catalysts with different sodium ion contents were prepared through sequential impregnation method. The structural and catalytic properties of the catalysts were studied by using various techniques combined with micro-reactor tests. The experimental results showed that PtSnNa/SUZ-4 catalysts exhibited high durability, high propylene selectivity and high stability with adequate sodium ion content. Sodium ion additives neutralized the strong acid sites and prevented the formation of coke. However, excess sodium ion not only reduced tin species to metallic tin, which reduced the catalyst activity by forming PtSn alloys, but also led to more Pt particles inside the pore of zeolite, which were easily deactivated by coke. It was found that catalysts with the sodium ion content at 0.5–1.5wt % led to the highest propane conversion and propylene selectivity.
1. Introduction
Bimetallic platinum-tin (Pt-Sn)-based catalysts have attracted much attention for their industrial application potential in recent years. [1–3]. They have been widely employed in many reactions, such as light paraffin dehydrogenation [1,4,5], alcohol oxidation [6,7] and the hydrogenation for carbonyl compounds [8,9] et al. Among these applications, dehydrogenation of propane to produce propylene is a significant petrochemical process for the rapidly increasing demand of propylene [10,11]. However, current reaction conditions suffer high temperature and low H2 partial pressure, which leads to undesirable thermal cracking reactions to coke and light alkanes and results in low product yield and eventually deactivation of the catalyst [11–13]. Therefore, developing an efficient catalyst with high activity, high stability and high propylene selectivity is urgently required. The conventionally employed PtSn/-Al2O3 is considered to be one of the most efficient catalysts for propane dehydrogenation, but is deficiency for their poor stability and weak durability after recoveries [10,14,15]. To resolve the problem, additives, including alkali metals (K, Na) and rare earth metals (La, Ce) have been employed to improve the catalysts [14,16–18].
4. Conclusions
In conclusion, sodium ion contents neutralized the strong acid sites on SUZ-4 zeolite and enhanced the catalyst durability and propylene selectivity by suppressing the side reactions in propane dehydrogenation processes. Although the reactivity of the catalyst might be lowered at the beginning of the reaction, the propylene selectivity and catalytic stability were largely improved, which was even more important factors in industrial production. However, over-addition of sodium ion largely deactivated the catalyst because of the decreased surface area and the reduction of Sn(II) to Sn(0), which led to PtSn alloys with Pt and reduced the catalyst activity. Over-addition of sodium ion also led to more Pt clusters inside the pores because of the neutralization of strong acid sites that allowed the entrance of Pt precursor (H2PtCl6) into zeolite channels. Since Pt inside the pores could be easily deactivated by coke deposition, the effect was harmful to catalyst. Therefore, an adequate addition of sodium ion additives is a key factor for the catalyst designing and it was found that addition of 0.5–1.5wt % sodium ion content should be the best protocol in PtSnNa/SUZ-4 catalyst designing.