Abstract
The assessment of the catalytic performance of “hybrid” metal/zeolite catalysts (based on FER or MFI structure and CuZnZr metal complexes) in the methanol dehydration step to DME has been studied in this work. The results clearly show that there is an important effect of the interaction between metal and acid sites affecting the acid catalyst performances. Additionally, deactivation, studied by means of a Timo-on-Stream (TOS) test, was affected by the type of zeolite structure used for hybrid catalyst preparation. The decrease in DME selectivity can be attributed to the cooperation of metal and acid sites in the production of different compounds (mainly methyl formate and dimethoxy methane) converting methanol and DME. The presence of these compounds (indicating different reaction pathways active) was found to be dependent on the zeolite structure and on the type of co-precipitation medium (water or ethanol) used to prepare the hybrid catalyst.
Highlights
DME is a colorless, non-toxic, non-corrosive organic compound that is receiving a renewed attention as alternative fuel for diesel engines [1] thanks to its high cetane number (55–60) and its low emissions of fine particles and NOx [2]
To verify whether the medium can somehow influence the catalytic activity of the samples, MFI-based catalyst was prepared by replacing ethanol with distilled water as a co-precipitation medium
The MFI and FER zeolites were tested in the dehydration reaction of methanol to dimethyl ether in the presence of metal compounds CuZnZr, in order to determine the effect of this phase on methanol conversion and selectivity towards DME
Summary
DME is a colorless, non-toxic, non-corrosive organic compound that is receiving a renewed attention as alternative fuel for diesel engines [1] thanks to its high cetane number (55–60) and its low emissions of fine particles and NOx [2]. One of the DME production processes that is receiving increasing attention, especially for the reduction of green-house emission, is the “one pot” hydrogenation of CO2 by using a “hybrid catalyst” obtained through the combination of an acid catalyst (typically zeolite due to its resistance to deactivation against water [3]) with a redox catalyst [4]. A great variety of catalysts have been studied for CO2 hydrogenation, paying attention to the metallic phase role and characteristics: Cu-ZnO [7,8,9], Pd [10,11] and other bimetallic catalysts [12]. Zirconia was found to be a promising promoter, and Cu-ZnO-ZrO2 catalysts have been investigated in combination with acidic functions of zeolites for the “one pot” production of DME [18,19,20,21,22]. CuZnZr/FER hybrid grain prepared by oxalate co-precipitation of metal precursors over zeolite crystals is considered a very active
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