Product Selectivity Controlled by Nanoporous Environments in Zeolite Crystals Enveloping Rhodium Nanoparticle Catalysts for CO2 Hydrogenation (original) (raw)
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Rhodium in basic zeolite Y: A stable, selective catalyst for CO hydrogenation
Journal of Molecular Catalysis
Zeolite-entrapped rhodium carbonyl clusters were prepared by reductive carbonylation of [Rh(CO)2(acac)] in the pores of zeolite Y made basic by treatment with NaN s. The samples were characterized as CO hydrogenation catalysts at 1-20 atm, 225-325 °C and H2/CO feed molar ratios of 0.5-3.0. Rh carbonyl clusters were formed and evidently entrapped in the strongly basic zeolite, and the catalyst was active for CO hydrogenation, at low conversions giving a non-Schulz-Flory distribution of C~-C5 hydrocarbons with high olefm to paraffin ratios. The catalyst was stable, operating at 300 °C and 20 atm with a H2/CO molar ratio of 1 for more than two weeks with no significant loss in activity and selectivity. High partial pressures of CO (or CO+ H2) stabilize the catalyst. The predominant rhodium species are suggested to be rhodium carbonyl clusters trapped in the zeolite cages. The results suggest opportunities for synthesis of metal clusters in strongly basic zeolites and for application of encaged metal dusters as catalysts for shape-selective conversions of synthesis gas.
Rhodium supported in basic zeolite Y: A selective and stable catalyst for CO hydrogenation
Catalysis Letters, 1991
Catalysts prepared by a condensation reaction of Rh(CO)2(acac) within the supercages of zeolite Y made basic by treatment with NaN 3 are active for CO hydrogenation and selective for low-molecular-weight olefins and methanol. High partial pressures of CO (or CO + H2) stabilize the catalyst. The predominant species in the catalyst are suggested to be rhodium carbonyl clusters trapped in the zeolite cages.
Inorganic Chemistry, 1988
This method can also be particularly powerful in cases where the EPR spectrum is very poorly resolved and yields no information, as is t h e case with t h e neutral paramagnetic compound [ ( $ -C , M e , ) Z r (~o t ) ] ;~~ ENDOR then becomes valuable in sup-plying the desired information without necessarily resorting to X-ray diffraction methods. Proton and 91Zr ENDOR studies on t h e latter compound are under way. Registry No. [CpTi(cht)], 51203-49-7; [CpTi(cht)]-, 115338-78-8; [(TI'-C,D,)T~(C~~)], 115338-79-9; [(s5-C5D5)Ti(cht)]-, 115338-80-2; (22) Blenkers, J.; Bruin, P.; Teuben, J. H. J. Orgonomet. Chem. 1985, 297, 61. THF, 109-99-9.
Nature Communications
Cascade processes are gaining momentum in heterogeneous catalysis. The combination of several catalytic solids within one reactor has shown great promise for the one-step valorization of C1-feedstocks. The combination of metal-based catalysts and zeolites in the gas phase hydrogenation of CO2 leads to a large degree of product selectivity control, defined mainly by zeolites. However, a great deal of mechanistic understanding remains unclear: metal-based catalysts usually lead to complex product compositions that may result in unexpected zeolite reactivity. Here we present an in-depth multivariate analysis of the chemistry involved in eight different zeolite topologies when combined with a highly active Fe-based catalyst in the hydrogenation of CO2 to olefins, aromatics, and paraffins. Solid-state NMR spectroscopy and computational analysis demonstrate that the hybrid nature of the active zeolite catalyst and its preferred CO2-derived reaction intermediates (CO/ester/ketone/hydrocarb...
Silica accelerates the selective hydrogenation of CO2 to methanol on cobalt catalysts
Nature Communications, 2020
The reaction pathways on supported catalysts can be tuned by optimizing the catalyst structures, which helps the development of efficient catalysts. Such design is particularly desired for CO 2 hydrogenation, which is characterized by complex pathways and multiple products. Here, we report an investigation of supported cobalt, which is known for its hydrocarbon production and ability to turn into a selective catalyst for methanol synthesis in CO 2 hydrogenation which exhibits good activity and stability. The crucial technique is to use the silica, acting as a support and ligand, to modify the cobalt species via CoO -SiO n linkages, which favor the reactivity of spectroscopically identified *CH 3 O intermediates, that more readily undergo hydrogenation to methanol than the CO dissociation associated with hydrocarbon formation. Cobalt catalysts in this class offer appealing opportunities for optimizing selectivity in CO 2 hydrogenation and producing high-grade methanol. By identifying this function of silica, we provide support for rationally controlling these reaction pathways.
Characterization of Rh-Co/SiO2 catalysts for CO2 hydrogenation with TEM, XPS and FT-IR
Applied Catalysis A: General, 2001
Rh-Co/SiO 2 catalysts, which showed remarkable methanol formation in CO 2 hydrogenation, were characterized by various methods such as TEM, EDX, XPS, and in situ FT-IR. The added amount of Co was varied from 0 to 2 in atomic ratio to Rh. The mean size of metal particles determined by TEM observation decreased with the amount of Co added. In addition, the metal particle size distribution of Rh-Co/SiO 2 catalysts observed by TEM was narrower than that of Rh/SiO 2 . EDX analysis of metal particle showed that Rh-Co alloy was formed on the Co-promoted catalysts. The results of XPS indicated that Co species existing on metal surfaces were more than 80 at.%. A good correlation was obtained between methanol selectivity and the surface Rh composition of Rh-Co/SiO 2 catalysts determined by XPS analysis. The selectivity to methanol increased with the surface composition of Rh. Adsorbed CO species on the Rh-Co alloy (cobalt rhodium carbonyl) were observed on Co-promoted catalysts in the spectra of in situ FT-IR during CO 2 hydrogenation reaction. These results indicated that methanol formation was promoted on the interface between Rh and Co. The electron-donating effect from Co to Rh was observed in situ FT-IR observation of CO 2 adsorption on Rh-Co/SiO 2 . Moreover, the temperature at which adsorbed CO species reacted with H 2 over Co-promoted Rh/SiO 2 catalysts was higher than that over unpromoted one. Judging from these findings of in situ FT-IR and CO 2 hydrogenation reactivity, it was concluded that adsorbed CO derived from CO 2 was stabilized by Co additive.
Effect of metal loading on CO2 hydrogenation reactivity over Rh/SiO2 catalysts
Applied Catalysis A: General, 2000
Silica supported Rh catalysts (Rh/SiO 2 ) with metal loading ranging from 1 to 10 wt.% were prepared by impregnation method and applied to CO 2 hydrogenation reaction. Characterization of surface species by TEM, H 2 chemisorption, XPS, EXAFS and FT-IR was carried out in order to elucidate the effect of metal loading on the CO 2 hydrogenation reactivity. The main product transformed from CO to CH 4 with the loading amount of Rh, retaining similar total activity. Judging from the results of EXAFS and FT-IR, formation of carbonyl species occurred on 1 wt.% Rh/SiO 2 catalyst. The concentration of Rh particles on SiO 2 surface had a significant influence on the reactivity. For 1 wt.% Rh/SiO 2 catalyst, the concentration of surface Rh particles was low, so Rh species were surrounded by hydroxyl groups of SiO 2 . CO-saturated Rh species, which were derived from dissociative CO 2 adsorption, reacted with surface hydroxyl groups to form relatively fine Rh carbonyl clusters, and adsorbed CO was not subjected to further hydrogenation, resulting in desorption as molecular CO. On the other hand, 10 wt.% Rh/SiO 2 catalyst achieved about 5.8 times more surface coverage of Rh species than 1 wt.% Rh/SiO 2 , based on the results of H 2 chemisorption. Therefore, too few surface hydroxyl groups of SiO 2 existed around Rh particles not to form Rh carbonyl clusters. The Rh surface was occupied by more hydride species and fewer CO species, resulting in CH 4 formation.
Nature Chemistry, 2021
With the advent of renewable carbon resources, multifunctional catalysts are becoming essential to hydrogenate selectively biomass-derived substrates and intermediates. However, the development of adaptive catalytic systems, that is, with reversibly adjustable reactivity, able to cope with the intermittence of renewable resources remains a challenge. Here, we report the preparation of a catalytic system designed to respond adaptively to feed gas composition in hydrogenation reactions. Ruthenium nanoparticles immobilized on amine-functionalized polymer-grafted silica act as active and stable catalysts for the hydrogenation of biomass-derived furfural acetone and related substrates. Hydrogenation of the carbonyl group is selectively switched on or off if pure H2 or a H2/CO2 mixture is used, respectively. The formation of alkylammonium formate species by the catalytic reaction of CO2 and H2 at the amine-functionalized support has been identified as the most likely molecular trigger for...
TECNICA ITALIANA-Italian Journal of Engineering Science, 2019
The production of DME from CO2 hydrogenation is a way of recycling CO2 and it requires the use of a hybrid multifunctional catalyst to efficiently catalyze the two consecutive reaction paths of methanol synthesis and methanol dehydration directly in one single step. The aim of this work is to investigate the utilization of zeolite-based catalysts for dimethyl ether synthesis by assessing the role of catalyst features in both methanol dehydration and one-pot CO2 hydrogenation. Obtained results, discussed in terms of turnover frequency reveal that FER-type zeolite prepared with Si/Al=10 exhibits the best performances during vapor-phase methanol dehydration whilst the efficiency of CO2-to-DME process strongly depends on the way in which metallic and acidic materials are coupled. Single grain prepared via gel-oxalate precipitation of CuZnZr over zeolite crystals exhibit the best performances in terms of CO2 conversion and DME productivity.
Applied Catalysis A: General, 2001
Silica-supported Rh catalysts (Rh/SiO 2 ) were prepared from acetate, chloride and nitrate precursors by an impregnation method and were applied to CO 2 hydrogenation reaction. CO 2 conversion over the catalyst prepared from chloride precursor was lower than that over acetate or nitrate one, because of fewer active sites on catalysts, as estimated by H 2 chemisorption. The main product was CO over the catalysts prepared from acetate and nitrate, but it was CH 4 over the catalyst prepared from chloride precursor. Characterization of catalysts by TEM, FT-IR and XPS was carried out in order to elucidate the effect of metal precursor on the CO 2 hydrogenation reactivity. The results of XPS showed that the O atomic ratio to Rh on surface hydroxyl groups increased in the order: chloride<nitrate<acetate precursor. The ratio of hydroxyl groups to Rh particles on SiO 2 surface was expected to have a significant influence on the reactivity. : S 0 9 2 6 -8 6 0 X ( 0 0 ) 0 0 5 7 6 -7