Metal-Exchanged β Zeolites as Catalysts for the Conversion of Acetone to Hydrocarbons.
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ABSTRACT:
SUBMITTER: Cruz-Cabeza AJ
PROVIDER: S-EPMC5448944 | biostudies-other | 2012 Jan
REPOSITORIES: biostudies-other
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Project description:Metal-organic frameworks (MOFs) have been an excellent platform for carbon dioxide reduction reactions (CO2RR). In this work, the feasibility of electrochemical reduction of CO2 to obtain C2-deep value-added products was investigated by the preparation of Mg-containing MOF-74 samples combined with transition metal cations (Ni2+, Co2+ and Zn2+). The prepared MOFs were used as electrocatalysts in CO2RR. Chronoamperometric analysis coupled to ATR-FTIR spectroscopy was employed to characterize the CO2 reduction products and subsequently via 1H NMR. Although an isostructural crystalline structure was observed in all synthesized MOFs, the pore diameter distribution was significantly affected due to the Mg coordination along with each transition metal nuclei with the organic ligand to form the MOF-74. Our results showed that Mg-containing MOF-74 electrocatalysts combined with Ni, Co and Zn ions successfully reduced CO2 to C2-deep products, while the monometallic Mg-MOF-74 showed only CO2 mineralization. An ester acetate, isopropyl alcohol, and formic acid were produced by Mg/Ni-MOF-74; isopropyl alcohol was provided by Mg/Co-MOF-74, and ethanol was generated by Mg/Zn-MOF-74. We observed that the change of the transition cation was a key factor in the selectivity of the obtained products, while the degree of Mg ions effectively incorporated into the MOF structure tuned the porosity and the electrocatalytic activity. Among them, Mg/Zn-MFOF-74 showed the highest Mg content loaded after synthesis and thus the most favorable electrocatalytic behavior towards CO2 reduction. Highlights • CO2-derived C2-deep reduction products were obtained by Mg-containing MOF-74 bimetallic electrocatalysts.• Mg-containing MOF-74 bimetallic electrocatalysts reduced CO2 to ester acetate, isopropanol, formic acid, and ethanol.• Mg/Zn-MOF-74 displayed the highest current density at a lower onset potential in CO2-saturated electrolyte.• The pore network could be tuned by the effective Mg content on a MOF-74 bimetallic sample.• Mg/Zn-MOF-74 showed the highest Mg content among all bimetallic electrocatalysts after the synthesis.
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Project description:In this paper, the ultrasonic-assisted desilication technique was reported as an attractive and efficient way for the preparation of hierarchical zeolites with MFI structure type. The prepared materials were used as active catalysts for the dehydration of ethanol into diethyl ether and ethylene. For all catalysts, the selectivity to diethyl ether was ca 95% or higher up to 210 °C, with catalytic activity in the range of 40-68%. In case of desilicated zeolites, at 270-290 °C, the conversion of ethanol was full with selectivity to ethylene ca 80%. MFI-type commercial zeolite was treated with a sodium and/or tetrabutylammonium hydroxide aqueous solutions (NaOH or NaOH/TBAOH) for 30 min. In the case of the application of ultrasounds, a QSonica Q700 sonicator (60 W and 20 kHz) equipped with a "1" diameter horn was used. In all cases, desilication was performed in an ice bath in order to keep the procedure conditions at low temperature. It was indicated that the use of ultrasounds during desilication procedure caused higher extraction of silicon and aluminum, which was connected with an elevated mesoporosity in relation to the samples modified in the absence of ultrasounds. Ultrasonic-assisted treatment of MFI-type zeolite caused also an apparent formation of numerous holes inside zeolite grains, resembling the look of "swiss cheese". Furthermore, it was indicated that the samples prepared using ultrasonic irradiation exhibited enhanced catalytic properties in the dehydration of ethanol. For instance, MFI-type zeolite treated with NaOH/TBAOH alkaline mixture containing 10 mol% of TBAOH in the presence of ultrasounds (M-10 s) demonstrated higher both conversion of ethanol (59% vs. 47%) and selectivity to diethyl ether (95% vs. 93%) in comparison with zeolite modified conventionally (M-10c). The best catalyst was zeolite ultrasonically desilicated with NaOH/TBAOH solution of 70 mol% of TBAOH (M-70s). Generally, this catalyst indicated the highest conversion of ethanol, very high selectivity to diethyl ether (94-100%) at 150-210 °C and the highest selectivity to ethylene among investigated catalysts (21%, 66% and 84%) at 230 °C, 250 oC and 270 °C.
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