Dual-bed Catalyst System Research Articles

Steering CO2 hydrogenation coupled with benzene alkylation toward ethylbenzene and propylbenzene using a dual-bed catalyst system

Utilization of CO2 as a C1 resource for the synthesis of aromatics is of great significance and is also related to carbon recycling. However, forming an ethylated or propylated side chain at the benzene ring by this strategy is difficult, and the products reported are methylated aromatics. Here, we show the first CO2 hydrogenation in tandem coupling with benzene alkylation to synthesize ethylbenzene and propylbenzene over a dual-bed system containing ZnZrOx, SAPO-34, and phosphorus-modified ZSM-5 catalysts. Controlled experiments and density functional theory studies reveal that the intermediate reactive species CHxO∗ (x = 1–3) of CO2 hydrogenation are preferentially alkylated with benzene to give methylated aromatics, rather than to form ethylated and propylated aromatics, when the three catalysts are simply mixed. By contrast, the three catalysts with rationally spatial distribution in the dual-bed system can afford 83.5% selectivity to ethylbenzene or 64.7% to propylbenzene in total aromatics without deactivation after 100 h.

Simultaneously Achieving High Conversion and Selectivity in Syngas-to-Propane Reaction via a Dual-Bed Catalyst System

Simultaneously Achieving High Conversion and Selectivity in Syngas-to-Propane Reaction via a Dual-Bed Catalyst System

Highly selective, energy-free, and environmentally friendly one-pot production of linear α-olefin from biomass-derived organic acid in a dual-bed catalyst system

An efficient and environmentally-friendly process to produce linear α-olefin from biomass-derived organic acid in a dual-bed catalyst system with high selectivity and stability.

Direct Conversion of CO2 into Dimethyl Ether over Al2O3/Cu/ZnO Catalysts Prepared by Sequential Precipitation

Bifunctional Al2O3/Cu/ZnO catalysts with Al composition of between 30 mol% and 80 mol% were prepared by sequential precipitation (SP) for the conversion of CO2 into dimethyl ether (DME). In the SP synthesis, the concentration of a precipitation agent managed to be high enough to induce the complete precipitation of Al3+. The prepared precipitates were composed of zincian malachite and amorphous AlO(OH). Furthermore, the calcined mixed metal oxide materials of 60% and 80% Al exhibited a higher acidity than commercial Al2O3 and the H2-reduced catalysts showed the similar Cu dispersion of 6%–7% at all Cu loadings. In the activity test at 573 K and 50 bar, the SP-derived catalyst of 80% Al (SP-80) displayed the best performance corresponding to CO2 conversion of 25% and DME selectivity of 75% that are close to equilibrium values. In order to overcome the thermodynamic limitation, a dual-bed catalyst system was made up of SP-80 in the first layer and zeolite ferrierite in the next. This approach enabled DME selectivity to be enhanced to 90% while CO2 conversion increased a little. Consequently, the studied catalyst system based on the SP-derived catalysts can contribute greatly to selective DME production from CO2.

Integrated Conversion of Cellulose to High-Density Aviation Fuel

Summary The catalytic conversion of renewable lignocellulose to transportation fuels is crucial to establish energy security and mitigate CO2 emissions. Here, we describe an effective and integrated strategy for the production of high-density aviation fuel with cellulose, an abundant and inedible raw biomass. First, cellulose was selectively converted to 2,5-hexanedione in a separation yield of 71.4%. Subsequently, a mixture of C12 and C18 branched polycycloalkanes was directly obtained in a carbon yield of 74.6% by the aldol condensation-hydrogenation and hydrodeoxygenation reaction of 2,5-hexanedione and hydrogen over a dual-bed catalyst system. The polycycloalkane mixture obtained by this process has high density (0.88 g mL−1) and low freezing point (225 K). In real application, they can be used as advanced aviation fuel or additives to improve the volumetric heat values of conventional aviation fuels.

Synthesis of jet fuel additive with cyclopentanone

Abstract A new route was developed for the synthesis of renewable decalin with cyclopentanone which can be derived from lignocellulose. It was found that 1,2,3,4,5,6,7,8-octahydronaphthalene could be selectively produced by the hydrogenation/dehydration/rearrangement of [1,1′-bi(cyclopentylidene)]-2-one (i.e. the self-aldol condensation product of cyclopentanone) over a dual-bed catalyst system. Among the investigated catalysts, the Ru/C and Amberlyst-15 resin exhibited the highest activities for the hydrogenation of [1,1′-bi(cyclopentylidene)]-2-one to [1,1′-bi(cyclopentan)]-2-ol and the dehydration/rearrangement of [1,1′-bi(cyclopentan)]-2-ol to 1,2,3,4,5,6,7,8-octahydronaphthalene, respectively. Using Ru/C and Amberlyst-15 resin as the first bed and the second bed catalysts, 1,2,3,4,5,6,7,8-octahydronaphthalene was directly produced in high carbon yield (83.7%) under mild conditions (393 K, 1 MPa). After being hydrogenated, the 1,2,3,4,5,6,7,8-octahydronaphthalene was converted to decalin which can be used as additive to improve the thermal stability and volumetric heat value of jet fuel.

Transformation of 2,3-butanediol in a dual bed catalyst system

The catalytic dehydration of 2,3-butanediol (BDO) was investigated over a dual bed catalyst system comprised of Sc2O3 as the first bed and Al2O3, silica-alumina, and zirconia doped with calcium and ceria as the second bed at temperatures between 300 °C and 400 °C. A dual bed reactor concept was chosen to productively couple two different chemistries to direct reaction towards specific products. Both Sc2O3 + alumina and Sc2O3 + silica alumina gave 1,3-butadiene (BD) selectivity of about 61%, while Sc2O3 + zirconia gave lower BD selectivities. Sc2O3 + zirconia produced 2,5-dimethylphenol with selectivity reaching 12% at a maximum. The BDO dehydration over a single bed of zirconia catalyst was studied at various residence times. 2,5-dimethylphenol concentration increased as the residence time increased. Possible intermediates to form 2,5-dimethylphenol from BDO are methyl vinyl ketone (MVK), 3-buten-2-ol (3B2OL) and acetoin. The first bed Sc2O3 selectively converted BDO to 3B2OL, while the second bed catalyst greatly affected the product distribution. Acidic oxides such as alumina oxide and silica alumina were better catalysts to convert 3B2OL to BD, while catalysts with basic sites, such as zirconia doped with ceria and calcium, catalyzed condensation reactions that ultimate lead to phenols like 2,5-dimethylphenol.

Dual bed catalyst system for oxidative dehydrogenation of mixed-butenes: a synergistic mechanism

Oxidative dehydrogenation (ODH) of mono and mixed-butenes to 1,3-butadiene (BD) was conducted using individual and dual bed catalyst systems, consisting of ZnFe2O4, Co9Fe3Bi1Mo12O51 or both. The dual bed catalyst system gave improved catalytic performance. A mechanism based on synergy between the catalysts is proposed to explain the improved overall butene conversion. The proportion of the reactants differed between the catalyst beds in the dual bed system, making better use of the catalytic activity of the second bed. The existence of all butene isomers inhibited isomerization, leading to a higher proportion of ODH reactions and thus improved the conversion of butene and the yield of BD. The packing sequences and the volume ratio of the catalysts in the bed were optimized. The results indicated that the sequence with ZnFe2O4 on top and a catalyst packing ratio of between 4:6 and 6:4 led to better activity.

Design of a dual-bed catalyst system with microporous carbons and urea-supported mesoporous carbons for highly effective removal of NOx at room temperature

A dual-bed catalyst system is designed for highly effective remove of NOx at room temperature, which consists of a microporous spherical activated carbon (SAC) layer and a urea-supported spherical mesoporous carbon (SMC) layer.

Direct synthesis of gasoline and diesel range branched alkanes with acetone from lignocellulose

C6–C15branched alkanes were synthesized in a high carbon yield (∼80%) with acetone and hydrogen over a dual-bed catalyst system.

Simulation of OHC/SCR process over Ag/Al2O3 catalyst for removing NOx from diesel engine

A reaction kinetic model was developed to describe the selective catalytic reduction of NOx over Ag/Al2O3 with ethanol as the reductant, which was then used for numerical simulation and optimization of the deNOx performance of the oxygenated hydrocarbon (OHC)/SCR process. Results of numerical simulation of the one-dimensional pseudo-homogeneous reactor model have demonstrated the capability of the model, describing reasonably well the general trends of the experimental data such as the conversions of NO and C2H5OH as well as the formation of N2, NH3, CO, CH3CHO, CO2, N2O and HOCH2CH2NH2 during the ethanol/SCR process with respect to the reaction temperature, the reactor space velocity and the C1/NOx feed ratio covered in the present study. After successful validation of the reactor model, the axial concentration profiles within the reactor were used for the optimal design of a dual-bed catalyst system to enhance the deNOx performance of the ethanol/SCR by best utilizing the reaction intermediates in the rear bed following the Ag/Al2O3 in the front bed. The methodology developed in this work may provide useful guidance on the design of an OHC/SCR system using ethanol as the reductant, including, but not limited to, the diesel engine operating on E-diesel fuel.

Enhanced NOx reduction and byproduct removal by (HC + OHC)/SCR over multifunctional dual-bed monolith catalyst

Selective catalytic reduction of NOx over Ag/Al2O3 monolith catalyst was investigated using a dodecane–ethanol mixture as the reductant, with special attention to the increased formation of harmful byproducts due to ethanol in the reductant hydrocarbon mixture. To compensate the tradeoff effect of ethanol by fully utilizing and/or efficiently removing these hazardous byproducts formed over the Ag/Al2O3 catalyst, additional catalysts were employed in a double-layer or dual-bed configuration, or a combination thereof. Among the catalysts tested, a trimetallic dual-bed monolith catalyst was identified as the best combination for the maximum NOx-to-N2 conversion (∼90% above 300°C) with a minimum formation of harmful byproducts, through multifunctional cooperative catalytic processes on Ag/Al2O3, CuCoY and Pd/Al2O3. Reaction intermediates formed on catalyst surfaces were investigated using an in situ DRIFT for both single-bed and dual-bed catalysts, thereby identifying three important roles of Ag/Al2O3 in the front bed. The relative importance of various deNOx processes occurring on CuCoY in the rear bed strongly depends on the reaction temperature and the gas space velocity over the dual-bed catalyst system. Reaction pathways of (HC+OHC)/SCR in the dual-bed catalyst system were discussed in light of the maximum NOx conversion with a minimum consumption of OHC.

Dual-bed catalyst system for improving product purity and catalytic stability in alkylbenzene transalkylation

A versatile catalyst system for the transalkylation of alkylbenzenes was developed, comprising Pt/ZSM-12 as the top bed catalyst and H-Beta as the bottom bed catalyst. The dual-bed catalyst system could improve the purity of the benzene product as well as the catalyst stability. The minimum ratio of H-Beta/ZSM-12 can achieve the industrial specification by interplaying the reaction temperatures, feed compositions, and the relative activities for the hydrogenation over Pt/ZSM-12 and the selective naphthene-cracking reaction rate over H-Beta. With increasing the trimethylbenzene (TMB) content of the feed mixture, the product yields of the dual-bed catalyst systems approached thermodynamic compositions due to the enhancement of the TMB reactivity; and the required amount of H-Beta and the minimum reaction temperature to meet benzene product specification became lower. Performance curves in terms of feed compositions, catalyst bed ratios, and reaction temperatures were constructed to aid the design of optimum dual-bed catalyst systems.

Metallic Ni monolith–Ni/MgAl 2O 4 dual bed catalysts for the autothermal partial oxidation of methane to synthesis gas

A dual bed catalyst system consisting of a metallic Ni monolith catalyst in the front followed by a supported nickel catalyst Ni/MgAl 2O 4 has been studied for the autothermal partial oxidation of methane to synthesis gas. The effects of bed configuration, reforming bed length, feed temperature and gas hourly space velocity on the reaction as well as the stability are investigated. The results show that the metallic Ni monolith in the front functions as the oxidation catalyst, which prevents the exposure of the reforming catalyst in the back to the very high temperature, while the supported Ni/MgAl 2O 4 in the back functions as the reforming catalyst which further increases the methane conversion by 5%. A typical 5 mmNi monolith–5mmNi/MgAl 2O 4 dual bed catalyst exhibits methane conversion and hydrogen and carbon monoxide selectivities of 85.3%, 91.5% and 93.0%, respectively, under autothermal conditions at a methane to oxygen molar ratio of 2.0 and gas hourly space velocity of 1.0 × 10 5 h −1. The dual bed catalyst system is also very stable.

Dual-bed catalyst system for C–C coupling of biomass-derived oxygenated hydrocarbons to fuel-grade compounds

Mono-functional intermediates produced by catalytic conversion of sugars and polyols over Pt–Re/C catalysts (consisting of alcohols, ketones, carboxylic acids, and heterocyclic compounds) can be upgraded to fuel-grade compounds using two catalytic reactors operated in a cascade mode. The first reactor achieves C–C coupling of mono-functional intermediates using a dual-bed catalyst system, where the upstream catalyst bed (Ce1Zr1Ox) is employed to carry out ketonization of carboxylic acids, and the downstream catalyst bed (Pd/ZrO2) is used to achieve aldol condensation/hydrogenation of alcohols and ketones. This second bed is not significantly inhibited by CO2 and H2O produced during ketonization. The high molecular weight ketones produced by C–C coupling reactions in the dual-bed catalyst system are subsequently converted to alkanes by hydrodeoxygenation (i.e., dehydration/hydrogenation) over a Pt/SiO2–Al2O3 catalyst. Using the aforementioned approach, an aqueous feed containing 60 wt% sorbitol was converted to a liquid stream of alkanes, 53% of which consisted of C7+ alkanes with minimal branching, desirable for Diesel fuel.

Metal Supported Zeolite for Heavy Aromatics Transalkylation Process

Aiming at improving the catalytic activity, benzene product purity, and catalyst stability during heavy transalkylation processes, strategies invoking startup procedures and catalyst system designs are summarized and discussed in this review. In particular, recent advances in the developments and catalytic performances of the on-line sulfiding technique, the selective pre-coking startup procedure, and a versatile dual-bed catalyst system design were compared and discussed.