Study on ethane dehydrogenation over PtSn-Mg(Zn)AlO catalyst

doi:10.11949/j.issn.0438-1157.20190569

Abstract

Abstract:

A series of PtSn-Mg(Zn)AlO catalysts with different Zn and Pt contents were synthesized by anion exchange method for ethane dehydrogenation. The experimental results show that the doping of a small amount of Zn in the hydrotalcite precursor has a significant effect on the performance of ethane dehydrogenation. When the Zn content is 2% (mass), the Pt-based catalyst exhibits the best performance with an initial ethane conversion of 27.1% and an average ethane conversion of 21.6% for a period of 2 h at 550℃. To study the effect of Zn doping on the performance of ethane dehydrogenation and the structure of catalyst, the prepared catalysts were characterized by XRD, BET, SEM and TEM. The BET and SEM results show that the PtSn-Mg(Zn)AlO catalyst has larger specific surface area than the PtSn-MgAlO catalyst. The TEM results show that the average diameter of the PtSn-Mg(Zn)AlO catalyst and the PtSn-MgAlO catalyst are (1.49 ± 0.31) nm and (2.0 ± 0.23) nm, respectively, which shows that the doping of Zn changes the structure of the catalyst to some extent, and better disperse Pt particles, thereby improving the catalyst reaction performance. Furthermore, the effect of temperature and Pt loading on the performance of ethane dehydrogenation were investigated. It was found that the ethane initial conversion was higher at higher temperatures, but the catalyst was more susceptible to deactivation. The effect of Pt loading on the dehydrogenation performance of ethane was investigated. It was found that increasing the Pt content did not increase the ethane conversion rate by a corresponding multiple, that is, increasing the Pt content reduced the utilization rate of Pt. Therefore, proper reduction of Pt content in Pt-based catalyst has far-reaching significance for studying the ethane dehydrogenation reaction.

Key words: chemical processes, Zn-modified, catalyst support, MgAl LDHs, catalyst, PtSn, ethane dehydrogenation

摘要：

采用阴离子交换法合成了一系列不同Zn和Pt含量的PtSn-Mg(Zn)AlO催化剂用于乙烷脱氢反应。实验结果表明，在水滑石载体中掺杂少量的Zn对乙烷脱氢反应有明显影响。当Zn含量为2%（质量）时Pt基催化剂活性性能最优，在550℃时乙烷初始转化率达到27.1%，2 h平均转化率为21.6%。BET和SEM结果表明PtSn-Mg(Zn)AlO催化剂比PtSn-MgAlO催化剂比表面积更大，TEM结果显示，PtSn-Mg(Zn)AlO催化剂和PtSn-MgAlO催化剂的金属颗粒的平均直径分别为（1.49±0.31）nm 和（2.0±0.23）nm，说明Zn的掺杂在一定程度上改变了催化剂的结构，能减小Pt颗粒的尺寸，更好地分散Pt颗粒，从而改善乙烷催化脱氢反应性能。此外，考察温度对乙烷脱氢反应性能影响，发现温度越高乙烷初始转化率越高，但催化剂越易失活；考察Pt负载量对乙烷脱氢反应性能的影响，发现增加Pt含量并不能使乙烷转化率得到相应倍数的增加，即增加Pt含量反而使Pt的利用率降低了，因此适量降低PtSn-Mg(2-Zn)AlO催化剂中Pt含量对研究乙烷脱氢反应有深远意义。

关键词: 化学过程, Zn改性, 催化剂载体, 镁铝水滑石, 催化剂, PtSn, 乙烷脱氢

CLC Number:

TQ 028.8

Xiaoping WU, Chenguang WANG, Qi ZHANG, Qiying LIU, Xinghua ZHANG, Longlong MA. Study on ethane dehydrogenation over PtSn-Mg(Zn)AlO catalyst[J]. CIESC Journal, 2019, 70(11): 4268-4277.

吴小平, 王晨光, 张琦, 刘琪英, 张兴华, 马隆龙. PtSn-Mg(Zn)AlO催化剂应用于乙烷脱氢反应研究[J]. 化工学报, 2019, 70(11): 4268-4277.

Figures/Tables 13

Fig.1 Schematic diagram of experimental setup for ethane dehydrogenation over PtSn-Mg(Zn)AlO catalyst

Fig.2 Effect of Zn loading on catalytic performances of PtSn-Mg(x-Zn)AlO catalysts in ethane dehydrogenation reaction

Fig.3 XRD patterns of Mg(x-Zn)AlO LDHs and PtSn-Mg(x-Zn)AlO catalysts

Table 1 BET surface area and pore volume of PtSn-Mg(x-Zn)AlO catalysts

Catalyst	Specific area A/(m²·g^-1)	Pore volume v/(cm³·g^-1)
PtSn-MgAlO	172.2	0.65
PtSn-Mg(1-Zn)AlO	210.3	0.74
PtSn-Mg(2-Zn)AlO	227.5	0.81
PtSn-Mg(3-Zn)AlO	225.6	0.79

Fig.4 SEM images of PtSn-MgAlO and PtSn-Mg(2-Zn)AlO

Fig.5 TEM images and size distribution of metal particles of PtSn-MgAlO catalyst and PtSn-Mg(2-Zn)AlO catalyst

Table 2 Metal dispersion values of PtSn-Mg(x-Zn)AlO catalysts determined

Catalyst	Metal dispersion /%
PtSn-MgAlO	27.7
PtSn-Mg(1-Zn)AlO	43.2
PtSn-Mg(2-Zn)AlO	54.3
PtSn-Mg(3-Zn)AlO	61.5

Fig.6 Zn 2p XPS peaks over PtSn-Mg(2-Zn)AlO

Fig.7 Effect of temperature on catalytic performances of PtSn-Mg(2-Zn)AlO catalysts in ethane dehydrogenation reaction

Fig.8 Effect of Pt loading on catalytic performances of x-PtSn-Mg(2-Zn)AlO catalysts in ethane dehydrogenation reaction

Fig.9 Relationship between Pt loading and average ethane conversion

Fig.10 Ethane conversion and ethene selectivity of ethane dehydrogenation reaction for PtSn-Mg(2-Zn)AlO catalysts in stability tests

Fig.11 Ethane conversion and ethene selectivity of ethane dehydrogenation reaction for PtSn-Mg(2-Zn)AlO catalysts in reaction-regeneration cycles

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