Methane Conversion to Ethylene and Aromatics on PtSn Catalysts

Abstract

Pt and PtSn catalysts supported on SiO2 and H-ZSM-5 were studied for methane conversion under nonoxidative conditions. Addition of Sn to Pt/SiO2 increased the turnover frequency for production of ethylene by a factor of 3, and pretreatment of the catalyst at 1123 K reduced the extent of coke formation. Pt and PtSn catalysts supported on H-ZSM-5 zeolite were prepared to improve the activity and selectivity to non-coke products. Ethylene formation rates were 20 times faster over a PtSn(1:3)/H-ZSM-5 catalyst with SiO2:Al2O3 = 280 in comparison to those over PtSn(3:1)/SiO2. H-ZSM-5-supported catalysts were also active for the formation of aromatics, and the rates of benzene and naphthalene formation were increased by using more acidic H-ZSM-5 supports. These catalysts operate through a bifunctional mechanism, in which ethylene is first produced on highly dispersed PtSn nanoparticles and then is subsequently converted to benzene and naphthalene on Brønsted acid sites within the zeolite support. The most active and stable PtSn catalyst forms carbon products at a rate, 2.5 mmol of C/((mol of Pt) s), which is comparable to that of state-of-the-art Mo/H-ZSM-5 catalysts with same metal loading operated under similar conditions (1.8 mmol of C/((mol of Mo) s)). Scanning transmission electron microscopy measurements suggest the presence of smaller Pt nanoparticles on H-ZSM-5-supported catalysts, in comparison to SiO2-supported catalysts, as a possible source of their high activity. A microkinetic model of methane conversion on Pt and PtSn surfaces, built using results from density functional theory calculations, predicts higher coupling rates on bimetallic and stepped surfaces, supporting the experimental observations that relate the high catalytic activity to small PtSn particles.

Nonoxidative methane activation, coupling, and conversion to ethane, ethylene, and hydrogen over Fe/HZSM‐5, Mo/HZSM‐5, and Fe–Mo/HZSM‐5 catalysts in packed bed reactor

“…Lower acidity of support resulted also in higher selectivity for ethylene and lower for aromatics. Formation rate of carbon products was 2.5 mmol of C/((mol of Pt) s), which is similar to Mo/HZSM‐5 catalyst . Lower acidity of zeolite support for Mo catalyst was also utilized by Sheng et al to shift the selectivity from aromatics toward ethylene .…”

“…Both platinum catalysts had higher conversion of methane at the same TOS than the prepared 2.5% Fe catalyst. PtBi catalyst had also higher selectivity to C 2 products, and PtSn catalyst exhibited similar selectivity to detected products. The most comparable is 2% Fe/HZSM‐5 catalyst prepared by Tan .…”

“…Formation rate of carbon products was 2.5 mmol of C/((mol of Pt) s), which is similar to Mo/HZSM-5 catalyst. 11 Lower acidity of zeolite support for Mo catalyst was also utilized by Sheng et al to shift the selectivity from aromatics toward ethylene. 13 They used the same structure-type zeolite as HZSM-5 but lowered the acidity by incorporation of boron atoms in the framework instead of aluminium.…”

Intermetallic Nanocatalysts from Heterobimetallic Group 10–14 Pyridine-2-thiolate Precursors

“…1,2,3,4 For example, compared to simple, single element metals, binary 10-14 intermetallics show enhanced catalytic activity, selectivity, and durability. 5,6,7 Among these, Pt-Sn nanocatalysts such as Pt3Sn and PtSn have been studied for a variety of reactions including alkane dehydrogenation, 8,9,10,11,12,13,14,15,16,17,18,19,20 electro-oxidation of CO, formic acid, and methanol fuel cells, 21,22,23,24,25,26 methane conversion to ethylene, benzene, and napththalene, 27 dehydroisomerization of butane to isobutene, 28 and highly selective hydrogenation of nitrobenzene to aniline, 29 3-nitrostyrene to 3-aminostyrene, 30 and of furfural to furfuryl alcohol. 31 Less studied are Pd-Sn and Ni-Sn binaries.…”

Catalytic Conversion of Methane at Low Temperatures: A Critical Review

“…were produced, whereas the methane conversion was lower than 0.3% 132 . These demonstrate that a higher temperature favours a higher methane conversion during the NOCM.…”