BIFUNCTIONAL СО/SIO2-Fe-ZSM-5-Al2O3 CATALYSTS FOR SYNTHESIS OF HYDROCARBONS OF ENGINE FRACTIONS
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Abstract:
The process of obtaining motor fractions of hydrocarbons on bifunctional Со/SiO2-Fe-ZSM-5-Al2O3, catalysts obtained by mixing has been studied. The effect of the method of introducing iron into a catalyst (in the form of reduced iron and its nitrate) at the molding stage is studied. The catalysts were tested in a continuous mode for 30 h at a gas volume velocity of 1000 h-1, a pressure of 2 MPa and a temperature of 240 ° C. It is shown that when iron is introduced in the form of a reduced powder, the temperature gradient in the catalyst bed decreases, and the selectivity for C5+ hydrocarbons increases by 6% in comparison with the catalyst sample without the addition of iron. It has been established that the introduction of iron into the catalyst in the form of a nitrate salt is a less effective method. It blocks the operation of polymerization and acid sites of bifunctional catalysts, contributes to a reduction in CO conversion and selectivity for C5+ hydrocarbons. It is shown that the introduction of iron significantly changes the group composition and molecular-mass distribution of the produced hydrocarbons - the shares of saturated hydrocarbons are increases, predominantly of a linear structure, the yield of olefins decreases. The obtained C5+ hydrocarbons mainly consist of gasoline and diesel fractions. The introduction of iron promotes an increase in the content of diesel fractions in synthesis products. Thus, with the introduction of iron in the form of a nitrate salt, the content of the diesel fraction increased by 1.2 times in comparison with the sample of a catalyst without iron.Keywords:
Bifunctional catalyst
Fraction (chemistry)
ZSM-5
Bifunctional catalyst
Physisorption
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Dimethyl ether
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A bifunctional MOF catalyst containing coordinatively unsaturated Cr3+ sites and palladium nanoparticles (Pd@MIL-101) has been used for the cyclization of citronellal to isopulegol and for the one-pot tandem isomerization/hydrogenation of citronellal to menthol. The MOF was found to be stable under the reaction conditions used, and the results obtained indicate that the performance of this bifunctional solid catalyst is comparable with other state-of-the-art materials for the tandem reaction: Full citronellal conversion was attained over Pd@MIL-101 in 18 h, with 86% selectivity to menthols and a diastereoselectivity of 81% to the desired (−)-menthol, while up to 30 h were necessary for attaining similar values over Ir/H-beta under analogous reaction conditions.
Citronellal
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The activity and selectivity of non-uniform bifunctional catalysts are treated in this paper. For a bifunctional reacting network similar to pure hydrocarbons reforming, the effect to different radial distribution profiles of both catalytic functions in the catalytic particle on the activity and selectivity were theoretically predicted using an arbitrary set of kinetic parameters.
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In recent years, bifunctional catalysts for the syngas-to-olefins (STO) reaction via the oxide–zeolite (OX–ZEO) strategy has been intensively investigated. However, the bifunctional catalyst containing H-SSZ-13 with a 100% H+-exchanging degree for the STO reaction has not been developed because of the high selectivity to paraffin. Here, we report a ZnCrOx + H–SSZ-13 bifunctional catalyst, which contains the submicron H–SSZ-13 with adequate acidic strength. Light olefins in hydrocarbon reached 70.8% at a CO conversion of 20.9% over the ZnCrOx + H–SSZ-13(23S) bifunctional catalyst at 653 K, 1.0 MPa, and GHSV = 6000 mL·g–1·h–1 after 800 min of STO reaction. The effect of CO and H2 on the C–C coupling was discussed by carrying out the methanol-to-olefins (MTO) reaction under a similar atmosphere as that of the STO reaction. H2 and CO should play a more dominant role than the conventional hydrogen transfer reaction on the undesired high selectivity of paraffins. These findings provide new insight into the design of the bifunctional catalyst for the STO process via the OX–ZEO strategy.
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Fischer-Tropsch synthesis (FTS) was carried out over bifunctional model catalysts prepared by physically mixing precipitated iron-based FTS catalysts (P-Fe) and H-ZSM-5. We adjusted the acidity of model catalysts by varying the ratio of P-Fe/H-ZSM-5 and the ratio of Si/Al in the H-ZSM-5. The physical mixing of H-ZSM-5 was adequate to supply the Brønsted acid sites (BAS), which are nonexistent in the P-Fe, to the bifunctional model catalysts without deteriorating the catalytic activity of P-Fe. As a result, we found a linear correlation between the cracking rate and the BAS concentration in the bifunctional process of FTS and cracking for the first time. Furthermore, the model catalysts showed high CO conversion (73–78 %), comparable to that of P-Fe (73 %), and improved C5–C20 selectivity with increased BAS concentration. The highest C5–C20 selectivity obtained in this study (72 wt%) was twice higher than that obtained in the P-Fe (36 wt%).
Fischer–Tropsch process
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Fluid catalytic cracking
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Bifunctional catalyst
Dimethyl ether
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We successfully prepared bifunctional catalysts with the distance between metallic and acid sites tuned at the nanometer scale. Sols of β-zeolite nanoparticles were synthesized and mixed in optimized conditions with a γ-AlOOH boehmite suspension to yield alumina/zeolite aggregates with a nanometer scale intimacy. The composition of the aggregate could be tuned from pure alumina to pure zeolite. Then, by carefully choosing the Pt precursor and the pH conditions, we were able to selectively deposit platinum, either on alumina or in zeolite domains. A subsequent, soft thermo-reduction step was applied that produced well-dispersed Pt nanoparticles either on alumina or in the zeolite nanodomains as confirmed by 3D tomography microscopy experiments. The catalytic properties of the obtained nanostructured catalysts were studied through n-heptane conversion. Comparison of these original bifunctional catalysts with monofunctional or conventional bifunctional catalysts showed the impact of the location of the metallic particles on the selectivity.
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Boehmite
Heptane
Nanometre
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A series of Cu-ZnO-ZrO_2 methanol synthesis catalysts with different ZrO_2 contents were prepared by coprecipitation and then mixed mechanically with HZSM-5 to obtain the bifunctional catalysts CuO-ZnO-ZrO_2/HZSM-5.The catalysts are characterized by XRD and TPR analysis and evaluated for the development of STD(synthesis gas-to-dimethyl ether) process.The addition of ZrO_2 improved the performance of the bifunctional catalysts.When the content of ZrO_2 is x(ZrO_2)=0.06,CO conversion,DME selectivity and the over-heating tolerance performance arrived the best.Based on the results of XRD and TPR analyses,it can be concluded that the addition of ZrO_2 is benefit for the active components to be dispersed finely in the bifunctional catalysts,which may prevent the catalysts from sintering at higher temperature and enhance the reduce capability of the catalysts also.
Dimethyl ether
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