Ultralow-Loading Pt/Zn Hybrid Cluster in Zeolite HZSM-5 for Efficient Dehydroaromatization

Abstract

Minimizing Pt loading without sacrificing catalytic performance is critical, particularly for designing cost-efficient hydrocarbon transformation catalysts. Here, we show that ultralow-loading (0.001–0.05 wt %) Pt- and Zn-functionalized HZSM-5 catalysts, prepared through simple ion exchange and impregnation, are highly active and stable for light alkane dehydroaromatization (DHA). The specific activity of benzene, toluene, and xylene is up to 8.2 mol/gPt/min (or 1592 min–1) over the 0.001 wt % Pt–Zn2/HZSM-5 catalyst during ethane DHA at 550 °C under atmospheric pressure. Additionally, such bimetallic Pt x –Zn y /HZSM-5 catalysts are highly stable in contrast to the monometallic Pt/HZSM-5 catalysts. The rate constant of deactivation (k deactiv), according to the first-order generalized power law equation model, for the bimetallic catalysts is up to 120 times lower than that of the monometallic counterparts, depending on the Pt loading. This breakthrough is achieved through the formation of the [Pt1–Zn n ]δ+ hybrid cluster, instead of Pt0 cluster–proton adducts, in the micropores of the ZSM-5 zeolite.

Dual-Bed Plasma/Catalytic Synergy for Methane Transformation into Aromatics

“…The C 2 –C 6 light alkanes and alkenes produced from the plasma-assisted methane activation can be converted into liquid aromatics through conventional thermocatalytic aromatization at relatively lower temperatures (≤550 °C) than direct methane aromatization. For example, ethane aromatization has been extensively studied more recently in our group. ,,, Propane and butane aromatization has been demonstrated by UOP/BP in the industry, known as the Cyclar process . Additionally, C 5 and C 6 alkenes are also highly active toward aromatization, although they were not widely studied for on-purpose aromatics production.…”

“…In order to increase the conversion of ethane to BTX (decreasing C 2 selectivity), a more efficient catalyst or higher reaction temperature is required. Higher BTX selectivity at the expense of ethane could be achieved by using Pt/Zn-HZSM-5 catalyst recently developed in our group . Specifically, with the present dual-bed plasma/thermocatalytic reaction system, we suggested that the residual gas phase byproducts can be recycled back to the plasma reactor, which can be further activated by the energetic electrons to form more active hydrocarbon species for aromatization.…”

“…Higher BTX selectivity at the expense of ethane could be achieved by using Pt/Zn-HZSM-5 catalyst recently developed in our group. 7 Specifically, with the present dualbed plasma/thermocatalytic reaction system, we suggested that the residual gas phase byproducts can be recycled back to the plasma reactor, which can be further activated by the energetic electrons to form more active hydrocarbon species for aromatization. As a result, only BTX will be collected as the final product if flare gas is used as the reactant.…”

“…For example, ethane aromatization has been extensively studied more recently in our group. 7,40,41,43 Propane and butane aromatization has been demonstrated by UOP/BP in the industry, known as the Cyclar process. 44 Additionally, C 5 and C 6 alkenes are also highly active toward aromatization, 45 although they were not widely studied for on-purpose aromatics production.…”

“…In the chemical industry, methane was mainly converted through high-temperature steam reforming for H 2 or syngas (a mixture of H 2 and CO) production . In order to produce liquid petrochemical feedstocks and fuels, the syngas was converted into methanol or hydrocarbons through high-pressure methanol synthesis or Fischer–Tropsch synthesis. , Methanol, light olefins, and paraffin from these processes can be further converted into aromatics or long-chain liquid hydrocarbons through the additional catalytic process. − These indirect high-temperature/pressure routes, however, are carbon and energy-intensive, and only economically lucrative at a very large scalenot suitable for distributed local/on-site conversion of flare gas and biogas.…”