Noble Metals Rh Research Articles

Coke-resistance over Rh–Ni bimetallic catalyst for low temperature dry reforming of methane

Methane and carbon dioxide can be converted into syngas using the prospective dry reforming of methane technology. Carbon deposition is a major cause of catalyst deactivation in this reaction, especially at low temperature. The superior stability of bimetallic catalysts has made their development more and more appealing. Herein, a series of bimetallic RhNi supported on MgAl2O4 catalysts were synthesized and used for low temperature biogas dry reforming. The results demonstrate that the bimetallic RhNi catalyst can convert CH4 and CO2 by up to 43% and 52% over at low reaction temperature (600 °C). Moreover, the reaction rate of CH4 and CO2 of RhNi–MgAl2O4 remains stable during the 20 h long time stability test, most importantly, there was no obviously carbon deposition observed over the spent catalyst. The enhanced coking resistance should be attributed to the addition of a little amount of noble metal Rh can efficiently suppress dissociation of CHX∗ species into carbon, and the high surface areas of MgAl2O4 support can also promote the adsorption and activation of carbon dioxide to generate more O∗ species. Balancing the rate of methane dissociation and carbon dioxide activation to inhibit the development of carbon deposition is a good strategy, which provides a guidance for design other high performance dry reforming of methane catalysts.

The Hydrogen-Storage Challenge: Nanoparticles for Metal-Catalyzed Ammonia Borane Dehydrogenation.

Dihydrogen is one of the sustainable energy vectors envisioned for the future. However, the rapidly reversible and secure storage of large quantities of hydrogen is still a technological and scientific challenge. In this context, this review proposes a recent state-of-the-art on H2 production capacities from the dehydrogenation reaction of ammonia borane (and selected related amine-boranes) as a safer solid source of H2 by hydrolysis (or solvolysis), catalyzed by nanoparticle-based systems. The review groups the results according to the transition metals constituting the catalyst with a mention to their current cost and availability. This includes the noble metals Rh, Pd, Pt, Ru, Ag, as well as cheaper Co, Ni, Cu, and Fe. For each element, the monometallic and polymetallic structures are presented and the performances are described in terms of turnover frequency and recyclability. The structure-property links are highlighted whenever possible. It appears from all these works that the mastery of the preparation of catalysts remains a crucial point both in terms of process, and control and understanding of the electronic structures of the elaborated nanomaterials. A particular effort of the scientific community remains to be made in this multidisciplinary field with major societal stakes.

Comparative biological effects of spherical noble metal nanoparticles (Rh, Pd, Ag, Pt, Au) with 4-8 nm diameter.

For a comparative cytotoxicity study, nanoparticles of the noble metals Rh, Pd, Ag, Pt, and Au (spherical, average diameter 4 to 8 nm) were prepared by reduction in water and colloidally stabilized with poly(N-vinyl pyrrolidone) (PVP). Thus, their shape, size, and surface functionalization were all the same. Size and morphology of the nanoparticles were determined by dynamic light scattering (DLS), analytical disc centrifugation (differential centrifugal sedimentation, DCS), and high-resolution transmission electron microscopy (HRTEM). Cell-biological experiments were performed to determine the effect of particle exposure on the viability of human mesenchymal stem cells (hMSCs). Except for silver, no adverse effect of any of the metal nanoparticles was observed for concentrations up to 50 ppm (50 mg L−1) incubated for 24 h, indicating that noble metal nanoparticles (rhodium, palladium, platinum, gold) that do not release ions are not cytotoxic under these conditions.

Exchanging noble and seminoble cations into zeolites by oxygen vacancy ion exchange (OVIE)

It is proposed that cation exchanged zeolites can be prepared by reacting their decationized forms, e.g., (SiO2)n(Al2O3)m, n ≥ 2m, with noble or seminoble metals and oxygen or ozone. The resulting oxide ions would very exoergically occupy vacancies in the zeolite framework and the cations would go to conventional extraframework positions. The noble metals Rh, Pd, Ir, Pt, and Au and the seminoble metals Ru, Ag, Re, Os, Hg, and Bi are suggested. A sample reaction using decationized zeolite LTA would be: 6Pd + 3O2 + Si12Al12O42 → Pd6Si12Al12O48. Decationized zeolites can be prepared by heating zeolites, especially high-Al zeolites, in their H+ or NH4+ forms, causing them to lose framework oxygen atoms as H2O. The reactions may occur by simply heating a mixture of starting materials in flowing oxygen or ozone, e.g., 6Pd + 3O2 + (NH4)12Si12Al12O48.nH2O → Pd6Si12Al12O48 + 12NH3 + (6 + n)H2O. This method may be extended to other inorganic ion exchangers.

Catalytic ethanolysis and gasification of kraft lignin into aromatic alcohols and H2-rich gas over Rh supported on La2O3/CeO2–ZrO2

Efficient catalytic ethanolysis and gasification of kraft lignin were conducted over a versatile supported catalyst Rh/La2O3/CeO2–ZrO2 to give high-value aromatic alcohols and H2-rich gas. The removal of phenolic hydroxyl group was the most prevalent reaction, and importantly, almost no phenols, undesired char and saturating the aromatic ring were detected. Meanwhile, the feedstock and solvent both played key roles in H2 generation that contributed to the hydrodeoxygenation of liquid components and made the whole catalytic process out of H2 supply. Reusability tests of catalyst indicated that the crystalline phase transition and agglomeration of support, the loss of noble metal Rh and carbon deposition were the possible reasons for its deactivation in supercritical ethanol. Comparing with water, methanol and isopropanol system, ethanol was the only effective solvent for the depolymerization process.

Activity of transition metal sulfides supported on Al2O3, TiO2 and ZrO2 in the parallel hydrodesulfurization of 1-benzothiophene and hydrogenation of 1-methyl-cyclohex-1-ene

Sulfided conventional transition metals Co, Ni, Mo, and W and noble metals Rh, Pd, Ir, Pt, and Re deposited over conventional support γ-Al2O3 (SBET = 262 m2g−1), and unconventional supports TiO2 (anatase, SBET = 140 m2g−1) and ZrO2 (baddeleyite, SBET = 108 m2g−1) were studied in the parallel hydrodesulfurization of 1-benzothiophene (HDS) and hydrogenation of 1-methyl-cyclohex-1-ene (o-HYD) at 360 °C and 1.6 MPa. Mo, W, Co, and Ni sulfided catalysts exhibited relatively low activity in both HDS and o-HYD. For these sulfides, the TiO2 and ZrO2 support effect relative to γ-Al2O3 varied by the factor 0.4–9.3. In contrast, the supported sulfides of Rh, Re, Pd, Pt, and Ir were highly active in HDS with low TiO2 and ZrO2 support effect relative to γ-Al2O3 (Rh/ZrO2 being an exception). Rh, Re, and Pd sulfided species exhibited relatively low activities in o-HYD reaction while Ir and Pt species exhibited high activities in o-HYD. The reference industrial bimetallic CoMo and NiMo Al2O3 supported catalysts exhibited desirable high HDS but low o-HYD activities.

High-throughput screening of small-molecule adsorption in MOF

Using high-throughput screening coupled with state-of-the-art van der Waals density functional theory, we investigate the adsorption properties of four important molecules, H2, CO2, CH4, and H2O in MOF-74- with = Be, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Zr, Nb, Ru, Rh, Pd, La, W, Os, Ir, and Pt. We show that high-throughput techniques can aid in speeding up the development and refinement of effective materials for hydrogen storage, carbon capture, and gas separation. The exploration of the configurational adsorption space allows us to extract crucial information concerning, for example, the competition of water with CO2 for the adsorption binding sites. We find that only a few noble metals—Rh, Pd, Os, Ir, and Pt—favor the adsorption of CO2 and hence are potential candidates for effective carbon-capture materials. Our findings further reveal significant differences in the binding characteristics of H2, CO2, CH4, and H2O within the MOF structure, indicating that molecular blends can be successfully separated by these nano-porous materials.

Rhodium Supported Hβ Zeolite for the Hydrogenation of Toluene

Noble metal Rh supported on a large pore high acidic zeolite Hβ has been explored as a hydrodearomatization catalyst. The detail kinetic study of hydrodearomatization of toluene over a 1 wt % Rh/Hβ was done in a continuous-downflow stainless steel catalytic fixed bed reactor at varied space time, toluene feed rate, hydrogen partial pressure, hydrogen to toluene mole ratio, temperature, and in the presence of dibenzothiophene. The time on stream data and reaction order with respect to toluene were measured and was found to be of first order. Fourier transform infrared (FTIR) spectra and chemical analysis of fresh and spent catalyst suggested the presence of surface carbon species and weight percent carbon was found to be 4.43%. It was observed that toluene conversion was increased on increasing H2 partial pressure and H2/feed mole ratio. The conversion is dependent on temperature and shows a well-defined maximum. The decrease of the catalyst activity in the presence of dibenzothiophene is mainly attributed to the adsorption and decomposition of dibenzothiophene (DBT) on the metal sites, which results in a loss of metal surface available for the reaction to take place and a higher coke formation reducing the fraction of acid sites available for toluene hydrodearomatization. A nonlinear semiempirical kinetic model was also developed to have the best fit with 12% error.

Oxidation Electronics: Bond—Band—Barrier Correlation and Its Applications

AbstractFor Abstract see ChemInform Abstract in Full Text.

L-edge x-ray-absorption systematics of the noble metals Rh, Pd, and Ag and the main-group metals In and Sn: A study of the unoccupied density of states in 4d elements.

X-ray-absorption L-edge spectra have been obtained for the noble metals Rh, Pd, and Ag and the main-group metals In and Sn. The systematics derived from these spectra reveal that (a) the x-ray-absorption near-edge structure (XANES) is primarily related to the density of states in these systems, (b) the energy distribution of the states above the Fermi level in noble metals is qualitatively consistent with the general band-theory description and semiquantitatively in agreement with the single-particle theory of M\uller, Jensen, and Wilkins, and (c) the ${L}_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}$ ``white-line'' intensity ratio depends on the distribution of the ${d}_{5/2}$ and ${d}_{3/2}$ population above the Fermi level and this distribution deviates significantly from the statistical distribution when the d band of the metal is nearly full. The applicability of XANES in the investigation of the charge-distribution systematics in 4d elements is discussed.