Supported Rh Catalysts Research Articles

Tuning the CO2 hydrogenation activity and selectivity of TiO2 nanorods supported Rh catalyst via secondary‐metals addition

AbstractSecondary‐metals promotion is key to tune the CO2 hydrogenation performance of Rh‐based catalyst. We describe the addition of Cu or Co in TiO2 nanorods supported Rh catalyst (viz., RhMx/TiO2), showing significant impact on the CO2 hydrogenation activity and productivity. Cu addition can promote the partial hydrogenation to alcohols (methanol and ethanol), whereas Co led to the deep hydrogenation to alkanes (CH4, C2H6). Comparative time‐resolved in situ DRIFTS studies with H2/D2 isotopic exchange further reveal that both surface adsorbed CO* and formates could be the key reaction intermediates during the CO2 hydrogenation over RhMx/TiO2 (especially the RhCu2.5/TiO2), in which the interaction strength of CO* regulated by secondary‐metals addition was key to tune the reaction pathways and productivity. The findings suggested that rational design of active metal sites, for example the synergy between Rh and secondary‐metals, is highly needed to promote the CO insertion and CC coupling to produce ethanol.

Construction of a Metal-Silica Interface for Semihydrogenation of Alkynes.

Fabricating optimum surface structures represents an attractive approach for synthesizing supported catalysts with high activity and specific selectivity. New active sites could be flexibly constructed via the strong metal-support interaction under the redox condition. Herein, we demonstrated the formation of a new Rh-Si surface on a silica-modified carbon nanotube supported Rh catalyst under the high-temperature reduction condition as well as a thin amorphous silica coating layer and weak chemisorption toward the CO molecule. The electronic interactions between Rh and Si, along with the particular structure, guarantee desirable catalytic performance for the semihydrogenation of phenylacetylene under mild conditions. This facile approach might be extensively used in constructing new active sites with robust activity and specific selectivity in diverse heterogeneous catalysis systems.

Hydrogenolysis of isosorbide to diols and triols over a heterogeneous SiO2-supported Rh catalyst

SiO2-supported Rh (Rh/SiO2) was an effective and reusable heterogeneous catalyst for the hydrogenolysis of isosorbide to diols and triols, and 58% total yield of diols and triols was achieved.

Promotional Effect of Ag on the Catalytic Decomposition of N2O in the Presence of O2 over the Al2O3-Supported Rh Catalyst

Promotional Effect of Ag on the Catalytic Decomposition of N₂O in the Presence of O₂ over the Al₂O₃-Supported Rh Catalyst

Direct NO decomposition over Rh-supported catalysts for exhaust emission control

Direct nitrogen oxide decomposition (DND) is a promising alternative to the selective catalytic reduction (SCR) of nitrogen oxides for emissions control, as it eliminates the need to inject reductants such as urea/ammonia. The present study investigates the implementation of Rh-supported metal oxides for the DND reaction. Rh supported on each of PrOX, TiO2, Al2O3, and CeO2 were characterized, and we found that initially the catalytic activity on Rh/PrOX and Rh/TiO2 was very high, though it deactivated over time due to strong poisoning by adsorbed oxygen. This deactivation by oxygen poisoning was verified through in-situ DRIFTS, XPS, NEXAFS, O2-TPD measurements and density functional theory (DFT) calculations, respectively. This catalytic deactivation was positively regenerated by reductive treatments with CO or H2. This study discovers the mechanism of DND deactivation and regeneration over Rh-supported metal oxides, which will provide significant insight into further development of DND.

Nitrogen‐containing Porous Organic Polymer Supported Rhodium Catalyst for Hydroformylation of Olefins

AbstractThe hydroformylation reaction of olefins with syngas (CO/H2) to manufacture aldehydes is one of the largest homogeneous catalytic processes. However, it is important to extend the use of Rh catalysts promoted by nitrogen ligands to heterogeneous system. In this study, a nitrogen‐containing porous organic polymer supported Rh catalyst (Rh/TImT‐TBPT) was successfully synthesized, as well as showed excellent catalytic activity (TOF=216 h−1) and selectivity of aldehydes (98 %) in the hydroformylation of 1‐octene. Furthermore, the catalytic performance of Rh/TImT‐TBPT in the hydroformylation of various olefins was also investigated, displaying outstanding results. The catalytic material was characterized by FT‐IR, XRD, XPS, TEM, SEM and TGA in detail. The characterization data showed that Rh species were highly dispersed on the support, leading to the good stability. More importantly, the Rh/TImT‐TBPT catalyst could be separated from the reaction system at the end of the hydroformylation, and then reused in the next cycle under optimized conditions.

Decoupling the Interfacial Catalysis of CeO2-Supported Rh Catalysts Tuned by CeO2 Morphology and Rh Particle Size in CO2 Hydrogenation

Decoupling the Interfacial Catalysis of CeO₂-Supported Rh Catalysts Tuned by CeO₂ Morphology and Rh Particle Size in CO₂ Hydrogenation

Switchable Tuning CO2 Hydrogenation Selectivity by Encapsulation of the Rh Nanoparticles While Exposing Single Atoms.

The switch of CO2 hydrogenation selectivity from CH4 to CO over TiO2 supported Rh catalysts is accomplished via selective encapsulation of Rh nanoparticles while exposing Rh single atoms by high-temperature reduction (HTR) according to their different strong metal-support interaction (SMSI) occurrence conditions, which can be reversed by subsequent oxidation treatment.

Structure-dependent activity and stability of Al2O3 supported Rh catalysts for the steam reforming of n-dodecane

Steam reforming of liquid hydrocarbon fuels is an appealing way for the production of hydrogen. In this work, the Rh/Al2O3 catalysts with nanorod (NR), nanofiber (NF) and sponge-shaped (SP) alumina supports were successfully designed for the steam reforming of n-dodecane as a surrogate compound for diesel/jet fuels. The catalysts before and after reaction were well characterized by using ICP, XRD, N2 adsorption, TEM, HAADF-STEM, H2-TPR, CO chemisorption, NH3-TPD, CO2-TPD, XPS, Al27 NMR and TG. The results confirmed that the dispersion and surface structure of Rh species is quite dependent on the enclosed various morphologies. Rh/Al2O3-NR possesses highly dispersed, uniform and accessible Rh particles with the highest percentage of surface electron deficient Rh0 active species, which due to the unique properties of Al2O3 nanorod including high crystallinity, relatively large alumina particle size, thermal stability, and large pore volume and size. As a consequent, Rh/Al2O3-NR catalyst exhibited superior catalytic activity towards steam reforming reactions and hydrogen production rate over other two catalysts. Especially, Rh/Al2O3-NR catalyst showed the highest hydrogen production rate of 87,600 mmol gfuel−1 gRh−1min−1 among any Rh-based catalysts and other noble metal-based catalysts to date. After long-term reaction, a significant deactivation occurred on Rh/Al2O3–NF and Rh/Al2O3-SP catalysts, due to aggregation and sintering of Rh metal particles, coke deposition and poor hydrothermal stability of nanofibrous structure. In contrast, the Rh/Al2O3-NR catalyst shows excellent reforming stability with negligible coke formation. No significantly sintering and aggregation of the Rh particles is observed after long-term reaction. Such great catalyst stability can be explained by the role of hydrothermal stable nanorod alumina support, which not only provides a unique environment for the stabilization of uniform and small-size Rh particles but also affords strong surface basic sites.

CO2 hydrogenation to methanol over Rh/In2O3–ZrO2 catalyst with improved activity

The In2O3 supported rhodium catalyst has been previously confirmed to be active for CO2 hydrogenation to methanol. In this work, the In2O3–ZrO2 solid solution was prepared and employed to support the rhodium catalyst. The deposition-precipitation method was applied to make the Rh catalyst highly dispersed. The catalyst characterization confirms that the use of ZrO2 optimizes and stabilizes the oxygen vacancies of In2O3, which causes the enhanced adsorption and activation of CO2. The highly dispersed Rh catalyst remarkably improves the hydrogenation ability of the In2O3–ZrO2 support. Compared to Rh/In2O3, the In2O3–ZrO2 supported Rh catalyst shows significantly higher activity with high methanol selectivity. For instance, at 300 °C and 5 MPa, the methanol selectivity over Rh/In2O3–ZrO2 reaches 66.5% with a space-time yield (STY) of methanol of 0.684 gMeOH h-1 gcat-1 and a CO2 conversion of 18.1%. The methanol selectivity and methanol STY at 300 °C is 19% and 26% higher than that of the Rh/In2O3 catalyst.

Influence of the framework on the catalytic performance of Rh-supported Zr-MOFs in the hydroformylation of n-alkenes

Three large pore crystalline zirconium-based metal-organic frameworks (Zr-MOFs) of different pore sizes (6–18 Å) and structure were synthesized and used for the preparation of the Rh-supported catalysts Rh@UiO-66, Rh@UiO-67, and Rh@MOF-808. The materials were characterized by XRD, FTIR, SEM/TEM, XPS, and nitrogen adsorption/desorption measurements. The catalytic performance was studied in the hydroformylation of olefins to the corresponding aldehydes. A series of n-alk-1-enes of different chain length was used to study the influence of the pore size and structure. The results show that the Zr-MOF-based catalysts are very active and show high aldehyde selectivity. The superior catalytic properties are assigned to the presence of highly dispersed active Rh sites located at the isolated zirconia moieties and the enhanced accessibility of sites via the large pores. Nevertheless, marked differences in the catalytic performance of the catalysts are observed, which are assigned to the different accessibility of Rh located at various secondary building units.

担持ロジウム触媒の三元触媒活性に及ぼす熱処理ガス条件の影響

担持ロジウム触媒の三元触媒活性に及ぼす熱処理ガス条件の影響

Effects of rhodium catalyst support and particle size on dry reforming of methane at moderate temperatures

• Dry reforming of methane at 400–600 °C over supported Rh catalysts was studied. • Catalyst activity depended on Rh particle size, support type, and acidic properties. • Specific activity increased with decreasing Rh particle size. • Rh/SiO 2 -TiO 2 performed the best, giving H 2 and CO yields of 1.8% and 4.2% at 400 °C. • Electron-deficient Rh δ+ species may improve the specific activity of the catalysts. Dry reforming of methane at 400–600°C was studied over Rh catalysts with different supports (SiO 2 , γ-Al 2 O 3 , α-Al 2 O 3 , TiO 2 , ZrO 2 , CeO 2 , Y 2 O 3 , SiO 2 -Al 2 O 3 , SiO 2 -MgO, SiO 2 -TiO 2 ), Rh particle sizes (1.5–15.6 nm), and acidic properties (acidic site density, 0.37–3.40 mmol g −1 ). Catalysts with a high density of strongly acidic sites (e.g., α-Al 2 O 3 , SiO 2 -MgO) showed low activity and gradually deactivated with time on stream; in contrast, catalysts with a low density of strongly acidic sites (e.g., TiO 2 , γ-Al 2 O 3 ) showed high, stable activity. Rh/SiO 2 -TiO 2 showed the best performance, with H 2 and CO yields of 1.8% and 4.2% at 400°C and yields 37.3% and 53.1% at 600°C, respectively. Catalyst activity depended strongly on Rh particle size; specific activity increased with decreasing particle size, indicating that Rh-catalyzed dry reforming of methane is structure-sensitive. The support type influenced not only the dispersion and reducibility of the Rh particles but also the specific activity of the catalysts. CO temperature-programmed desorption and FT-IR suggested that electron-deficient Rh δ+ species were generated by electronic interactions between the Rh particles and the support, and the number of these species strongly influenced the overall catalytic activity.

Oxygen Release and Storage Property of Fe-Al Spinel Compounds: A Three-Way Catalytic Reaction over a Supported Rh Catalyst.

We evaluated the catalytic performance of the Rh-Fe/Al2O3 catalyst during a three-way catalytic reaction and found, by chance, that a part of Fe species was dissolved into the γ-Al2O3 support and worked as an oxygen storage material, which adjusts the oxygen concentration around the catalytically active sites to a suitable level for three-way catalysis. In this study, we demonstrated that the Fe-doped γ-Al2O3 can reversibly store and release oxygen by the redox of Fe2+/Fe3+ at the tetrahedral (Td) site of the spinel structure without its structure deformation. The finding that a spinel-structured metal oxide, Fe-doped γ-Al2O3, could work as an oxygen storage material suggested a new opportunity for the development of oxygen storage materials without rare metals.

Toward Continuous-Flow Hyperpolarisation of Metabolites via Heterogenous Catalysis, Side-Arm-Hydrogenation, and Membrane Dissolution of Parahydrogen.

Side-arm hydrogenation (SAH) by homogeneous catalysis has extended the reach of the parahydrogen enhanced NMR technique to key metabolites such as pyruvate. However, homogeneous hydrogenation requires rapid separation of the dissolved catalyst and purification of the hyperpolarised species with a purity sufficient for safe in-vivo use. An alternate approach is to employ heterogeneous hydrogenation in a continuous-flow reactor, where separation from the solid catalysts is straightforward. Using a TiO2 -nanorod supported Rh catalyst, we demonstrate continuous-flow parahydrogen enhanced NMR by heterogeneous hydrogenation of a model SAH precursor, propargyl acetate, at a flow rate of 1.5 mL/min. Parahydrogen gas was introduced into the flowing solution phase using a novel tube-in-tube membrane dissolution device. Without much optimization, proton NMR signal enhancements of up to 297 (relative to the thermal equilibrium signals) at 9.4 Tesla were shown to be feasible on allyl-acetate at a continuous total yield of 33 %. The results are compared to those obtained with the standard batch-mode technique of parahydrogen bubbling through a suspension of the same catalyst.

Ultralow Rh Bimetallic Catalysts with High Catalytic Activity for the Hydrogenation of N-Ethylcarbazole

Liquid organic hydrogen carrier (LOHC) has attracted a great deal of attention in recent years for its use in hydrogen storage. Supported Rh catalyst has been widely used in the hydrogenation react...

Structure-sensitivity of direct oxidation methane to methanol over Rhn/ZrO2-x (1 0 1) (n = 1, 4, 10) surfaces: A DFT study

The size-dependence of methane direct oxidation to methanol over Rhn/ZrO2-x (101) (n = 1,4,10) was studied by density functional theoretical (DFT) calculations. We envisioned several paths for methanol formation using H2O2 or O2 as oxidant respectively. The CH3* directly oxidized to methanol by OOH* was considered the optimal route for methanol formation over Rhn/ZrO2-x (101) in our present calculation. Moreover, the C-O bond formation via the O* as the oxidant shown a higher barrier than that of OH* or OOH*, indicating more active of H2O2 than O2 due to more available Rh sites. More importantly, the high stability of CH3* favors the CH3OH formation. With the increasing of the size of clusters, the activation energy of H* abstracted from CH3* was decreased, resulting in a reduction of methanol formation as Rh size growths. Besides, the larger Rh clusters were more facility for methanol decomposition to CO than Rh1/ZrO2-x (101), leading the lower productivity for methanol further. Especially for Rh4/ZrO2-x (101) and Rh10/ZrO2-x (101), the surface was even poisoned by CO. From the view of kinetic, our present results show that the methanol formation rate increased with increasing the Rh dispersion, particularly for the atomically dispersed Rh catalyst. So, the atomically dispersed Rh catalyst has the higher productivity and selectivity for the methanol production, which means a strongly structure-sensitivity for methanol formation catalyzed by supported Rh catalysts.

Promoted Hydroformylation of Formaldehyde By Electronic Metal–Support Interactions in N-Group Functionalized Silica Supported Rhodium Catalyst

The influence of surface modification of SiO2 carrier by grafting method and its effects for Rh supporting was investigated on formaldehyde hydroformylation reaction. The relationship between the structure of catalysts and their performance was characterized in detail by X-ray diffraction, N2 adsorption–desorption, temperature programmed reduction with H2, X-ray photoelectron spectroscopy, and in situ infrared. After grafting the amino organic functional group, the surface circumstance of SiO2 was altered, and moreover, sites available for metal loading was enriched on the carrier that distribute a high dispersion of Rh species Under the same Rh loading, the Rh@N–SiO2 catalyst exhibits better catalytic activity than pristine SiO2 supported Rh catalysts. Spectroscopic evidences suggest the presence of an electronic perturbation between Rh and modified SiO2 which promotes the hydroformylation of formaldehyde by maintaining Rh at proper Rh0/(Rh3+ + Rhδ+) ratio. Diagram of the effect of surface modified with amino group on metal rhodium loading.

Influence of crystal structure of Y-doped ZrO<sub>2</sub> as support oxide on the three-way catalytic performance of supported Rh catalyst

Influence of crystal structure of Y-doped ZrO<sub>2</sub> as support oxide on the three-way catalytic performance of supported Rh catalyst

Calcined hydrotalcites of varying Mg/Al ratios supported Rh catalysts: highly active mesoporous and stable catalysts toward catalytic partial oxidation of methane

Calcined hydrotalcites of varying Mg/Al ratios supported Rh catalysts: highly active mesoporous and stable catalysts toward catalytic partial oxidation of methane