Hongyuan Luo

Effects of zirconia phase on the synthesis of higher alcohols over zirconia and modified zirconia

The catalytic performances of ZrO2-based catalysts were evaluated for the synthesis of higher alcohols from synthesis gas. The crystal phase structures were characterized by X-ray diffraction (XRD) and UV Raman. The results indicated that ZrO2 and Pd modified ZrO2 catalysts were effective catalysts in the synthesis of ethanol or isobutanol, and their selectivities basically depended on the crystal phase of ZrO2 surface. The ZrO2 with surface tetragonal crystal phase exhibited a high activity to form ethanol, while the ZrO2 with surface monoclinic crystal phase exhibited a high activity to form isobutanol. Temperature-programmed desorption (TPD) experiment indicated that the high activity of isobutanol formation from synthesis gas over monoclinic zirconia was due probably to the strong Lewis acidity of Zr4+ cations and the strong Lewis basicity of O2− anions of coordinative unsaturated Zr4+–O2− pairs on the surface of monoclinic ZrO2.

The role of Mn and Li promoters in supported rhodium catalysts in the formation of acetic acid and acetaldehyde

Abstract RhMnLi/SiO 2 catalysts consisting of 1 wt% Rh for the synthesis of C 2 oxygenates from syngas were studied by CO + H 2 reaction and characterized by TPR, H 2 -TPD, ESR and IR techniques. The RhMnLi/SiO 2 catalysts, which showed a good selectivity for the formation of acetic acid and acetaldehyde, have been found to be quite different from the RhV/SiO 2 catalysts reported previously, which mainly promoted the formation of ethanol. Comparing with the RhV/SiO 2 catalysts, the RhMnLi/SiO 2 exhibited lower capacity of hydrogen adsorption, lower hydrogenation activity, more intense interaction of the manganese oxide with the Rh component, and more intense bands of twin-adsorbed CO (i.e. more Rh 1+ ion). The good selectivity of the RhMnLi/SiO 2 catalysts towards acetaldehyde and acetic acid formation were correlated to these features.

Characterization of Rh-based catalysts with EPR, TPR, IR and XPS

Rh-based catalysts to be used for the synthesis of c-2-oxygenates from syngas were characterized with epr, tpr, ir and xps methods. the chemical state of the mn component was extensively studied with epr after in situ reduction and treatment with various probe molecules. the results indicated that on the mn/sio2 catalyst, mn can exist as isolated mn2+ ions on the surface of sio2 through the formation of coordination compounds with surface hydroxyls and h2o molecules as ligands. thermal reduction of the mn/sio2 catalyst resulted in the migration and accumulation of the mn2+ ions. the results of tpr, ir, xps were consistent with those of epr, which indicated that on a rh-mn/sio2 catalyst, a rh-mn mixed oxide was formed, which stabilized the rh+ species. the formation of small clusters of the rh-mn mixed oxide inhibited deep reduction and accumulation of the mn component, while at the same time increased the dispersion of the rh component. as a promoter, mn acts as an electron acceptor, while li exhibits an electron-donation effect. the li component can inhibit the formation of rh-mn mixed oxide and increase the concentration of rh-0 on the surface of sio2. the existence of li may also cause the tilted-adsorption form of co on rh, as well as the spillover of h-2 from rh to the sio2 support. (c) 1999 elsevier science b.v. all rights reserved.

Supported rhodium and supported aqueous-phase catalyst, and supported rhodium catalyst modified with water-soluble TPPTS ligands

Two types of novel catalysts: supported rhodium and supported aqueous-phase (SAP/Rh-SiO2), and supported rhodium modified with water-soluble TPPTS ligands (TPPTS-Rh/SiO 2), were prepared. Hydroformylation of 1-hexene showed that SAP/Rh-SiO2 and TPPTS-Rh/SiO2 catalyst processed high activity for aldehydes and especially high selectivity towards aldehydes and high n/i- ratio of aldehydes. These results were significantly different from the performances of Rh/SiO 2 catalyst, but very comparable to those of SAP catalyst. 31 P NMR spectrum of TPPTS-Rh/SiO2 catalyst demonstrated that TPPTS ligands chemically bonded to highly dispersed rhodium metal particles. It make clear the reason that yield of aldehydes of SAP/Rh-SiO2 was nearly the sum of the yield of SAP catalyst and the yield of TPPTS-Rh/SiO2 catalyst, while all of catalytic selectivities were equal, because SAP/Rh-SiO2 was actually made up of SAP and TPPTS-Rh/SiO2 catalysts. The catalytic performance of TPPTS-Rh/SiO2 catalyst strongly depended on the molar ratio of P:Rh, which was similar to that of SAP catalyst to a certain extent.

Synthesis of C2+-oxygenated compounds directly from syngas

Abstract Vapor Phase synthesis of C2+-oxygenated compounds from synthesis gas was carried out on a bench-scale apparatus. A Rh-Mn/Sio2 catalyst showed an enhanced performance in terms of product selectivity anddurability.

Synthesis and surface characteristics of zirconia and modified zirconia: Performance of CO hydrogenation

ZrO2-A and ZrO2-B catalysts were prepared by two different coprecipitation methods and their performance of CO hydrogenation was studied. The results indicated that ZrO2 and Li-, Pd- and Mn-modified ZrO2 catalysts exhibited good selectivity and high STY to higher alcohols. The surface characteristics of ZrO2-A and ZrO2-B samples were investigated by means of BET, NH3-TPD, XRD and UV Raman technique. The tetragonal zirconia on the surface region of ZrO2-A and Li-Pd-Mn/ZrO2-A catalysts may be responsible for the high selectivity towards ethanol, while the monoclinic zirconia on the surface of ZrO2-B and Li-Pd-Mn/ZrO2-B catalysts may be crucial to the high isobutanol selectivity.

The promotion effects of Mn, Li and Fe on the selectivity for the synthesis of C2 oxygenates from syngas on rhodium based catalysts

Abstract Rh-based catalysts with the promoters of Mn, Li and Fe were prepared. The activity of the catalyst for C2 oxygenates formation enhanced with the addition of additives. The promotion effects of these additives were investigated by means of FT-IR, CO-TPD and TPSR of adsorbed CO with H2. IR results suggested that Fe, Mn and Li might be in close contact with Rh, and formed new active sites, which promoted CO activation on Rh surface and favored the formation of C2 oxygenated intermediates. The results of CO-TPD and TPSR showed that only a part of adsorbed CO on the catalyst could be hydrogenated into CH4. The ratio of CH4 quantity in TPSR to that of desorbed CO in CO-TPD on various catalysts was calculated, and it decreased in the order: Rh/SiO2 >Rh-MrdSiO2 >Rh-Mn-Li/SiO2 >Rh-Mn-Li-Fe/SiO2,whichimpliedthat non-dissociated CO increased in the reverse order. Which was consistent with the catalytic activity of C2 oxygenates formation sequence. The improvement of the space-time yield (STY) and selectivity towards C2 oxygenates could be explained based on that the increase of the nondissociative CO and the decrease of dissociative CO on the catalyst favored the insertion of CO into CHx.

Interactions among Rh, Mn and Li components in the Rh-based catalysts

Rh-based catalysts were used for the synthesis of C 2 -oxygenates from syngas under a medium syngas pressure (3.0Mpa). Addition of promoters such as Mn and Li enhanced the activity and selectivity of the Rh/SiO 2 catalyst pronouncedly. EPR, TPR and IR methods were employed to characterize the Rh-based catalysts in order to ascertain the promoting effects of Mn and Li. The results of EPR after in-situ reduction indicated that on the Rh-Mn/SiO 2 catalyst a Rh-Mn mixed oxide was formed, and this might be responsible for the enhancement of the catalytic activity. Further addition of Li weakened the interaction between the Rh and Mn components, and might also cause the spillover of H 2 from Rh to the SiO 2 support, resulting in the increase of the selectivity and the yield of C 2 -oxygenates.

Decomposition of ethanol on Rh(100) and Rh(100)c(2×2)-Mn surfaces

Decomposition of Ethanol on Rh(100) and Rh(100)c(2×2)-Mn surfaces was studied by HREELS, TDS, AES, UPS and LEED. On Rh(100) surface, a certain amount of the adsorbed molecular ethanol desorbed at 165 K and the remainder became surface ethoxide groups and H adatoms. Then, from 230 to 280 K, the ethoxide species decomposed, resulting in the formation of a surface with bridge adsorbed CO, CH 3 , CH 2 , and H. The formation of a Rh(100)c(2×2)-Mn surface implies that the addition of the Mn promoter into supported Rh catalysts will enhance the, dispersion of the Rh crystallines and will cause bonds to be formed between Rh and Mn. On the Rh(100)c(2×2)-Mn surface, the surface ethoxide species could exist up to about 500 K, and this may very probably be the cause of enhancement for the selectivity towards the C 2 -oxygenates.