R. Romero-Rivera

Bio: R. Romero-Rivera is an academic researcher from Autonomous University of Baja California. The author has contributed to research in topics: Catalysis & Thermal decomposition. The author has an hindex of 6, co-authored 7 publications receiving 349 citations.

HDS of DBT with Molybdenum Disulfide Catalysts Prepared by In Situ Decomposition of Alkyltrimethylammonium Thiomolybdates

Abstract: Three alkyltrimethylammonium thiomolybdates, [R–N(CH3)3]2MoS4 (where R = lauryl, myristyl or cetyl) were synthesized in aqueous solution, and characterized by 1H-NMR spectroscopy. These alkyltrimethylammonium thiomolybdates were used (the lauryl and myristyl thiomolybdates for the first time) as precursors for in situ prepared MoS2 catalysts, activated during the hydrodesulfurization of dibenzothiophene. The catalysts were analyzed by EDX, showing large voids and a S/Mo ratio around 2. High surface areas up to 443 m2/g and type IV adsorption–desorption nitrogen isotherms were obtained. X-ray diffraction showed that the catalysts are poorly crystalline, with a very weak (002) peak intensity for all samples except the MoS2 catalyst prepared from pure ammonium tetrathiomolybdate precursor. A high dibenzothiophene conversion (74%) was observed with the catalyst obtained from the lauryltrimethylammonium thiomolybdate precursor, attributed mainly to its high specific surface area. Selectivity results showed that all the prepared catalysts strongly favored the hydrogenation pathway.

CoMoW sulfide nanocatalysts for the HDS of DBT from novel ammonium and alkyltrimethylammonium-thiomolybdate-thiotungstate-cobaltate (II) precursors

Abstract: Five unsupported, highly active CoMoW trimetallic nanocatalysts were obtained by in situ decomposition from five novel precursors: (NH 4 ) 2 [Co(MoS 4 )(WS 4 )] and (RN(CH 3 ) 3 ) 2 [(MoS 4 )(WS 4 )] (where R = dodecyl, tetradecyl, cetyl and octadecyl), during the HDS of DBT. The catalyst labeled CoMoWS-C14, derived from the precursor containing the tetradecyl group, exhibits the highest catalytic activity ( k = 421 × 10 −7 mol/g s). N 2 adsorption–desorption shows that the CoMoW catalysts are mesoporous materials with characteristic Type IV isotherms, having surface areas of 11–340 m 2 /g. Elemental analysis by X-ray energy dispersive spectroscopy (EDS) working at STEM mode finds high concentrations of carbon (3.7 ≤ C/Mo ≤ 11.3 and 2.7 ≤ C/W ≤ 9) in all the catalysts except CoMoWS, where carbon was not detected. The XRD patterns show that the catalysts are highly dispersed (less so for the CoMoWS) given the absence of the (0 0 2) reflection, along with broad and low intensity (1 0 1) and (1 1 0) reflections. High dispersion is also supported by the STEM micrographs showing unstacked layers. The selectivity of the reaction for all catalysts favors the direct desulfurization pathway. The surface area and high catalytic activity do not show direct correlation with the length of the hydrocarbon chains of the precursors.

Trimetallic NiMoW sulfide catalysts by the thermal decomposition of thiosalt blends for the hydrodesulfurization of dibenzothiophene

Abstract: A series of unsupported trimetallic NiMoW sulfide catalysts were synthesized by ex situ decomposition from mechanically prepared blends of [Ni(en)3]MoS4, a novel precursor, and (NH4)2WS4 N2 adsorption–desorption shows that the NiMoW catalysts are mesoporous materials with characteristic Type IV isotherms, having surface areas of 144–524 m2/g Elemental analysis by X-ray energy dispersive spectroscopy (EDS) working in STEM mode finds high carbon/metal ratios (23 ≤ C/Mo ≤ 142 and 22 ≤ C/W ≤ 176) The XRD diffractograms of the NiMoW catalysts point to highly dispersed structures, given the absence of the (002) peak, as well as the broad and weakly intense (101) and (110) peaks; the nickel sulfide phase is barely detected High dispersion is also evidenced by TEM microscopy showing unstacked atomic layers The catalyst labeled NiMoW-020, exhibits the highest catalytic activity (k = 477 × 10−7 mol/g s) The NiMoW catalysts follow a zeroth order rate law Increasing catalyst atomic ratio (more nickel sulfide phase) favors the desulfurization route

Molecular assembly of multi-wall carbon nanotubes with amino crown ether: synthesis and characterization.

Abstract: Synthetic methodology and physicochemical characterization of multi-wall carbon nanotubes (MWCNTs) functionalized with a crown ether molecule is reported. The MWCNTs were synthesized by spray pyrolysis technique using toluene as carbon source and ferrocene as catalyst. The nanotubes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Oxidation of MWCNTs was carried out by 8 h of sonication in a mixture of sulfuric and nitric acid (3:1). The MWCNT-COOH was amidated with 4-aminobenzo-15-crown-5 under mild reaction conditions using N,N'-dicyclohexylcarbodiimide and dimethylaminopyridine as catalyst and dimethylformamide as solvent, at room temperature for 24 h. The amidation product was characterized by scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and a mass spectrometry study to determine the fragmentation pattern being m/z 309, 177 and 149 the most important ions.

Methods for carbon nanotubes synthesis—review

Abstract: Carbon nanotubes (CNTs) have been under scientific investigation for more than fifteen years because of their unique properties that predestine them for many potential applications. The field of nanotechnology and nanoscience push their investigation forward to produce CNTs with suitable parameters for future applications. It is evident that new approaches of their synthesis need to be developed and optimized. In this paper we review history, types, structure and especially the different synthesis methods for CNTs preparation including arc discharge, laser ablation and chemical vapour deposition. Moreover, we mention some rarely used ways of arc discharge deposition which involves arc discharge in liquid solutions in contrary to standard used deposition in a gas atmosphere. In addition, the methods for uniform vertically aligned CNTs synthesis using lithographic techniques for catalyst deposition as well as a method utilizing a nanoporous anodized aluminium oxide as a pattern for selective CNTs growth are reported too.

Transition-metal Doped Edge Sites in Vertically Aligned MoS2 Catalysts for Enhanced Hydrogen Evolution

Abstract: Highly active and low-cost catalysts for electrochemical reactions such as the hydrogen evolution reaction (HER) are crucial for the development of efficient energy conversion and storage technologies. Theoretical simulations have been instrumental in revealing the correlations between the electronic structure of materials and their catalytic activity, and guide the prediction and development of improved catalysts. However, difficulties in accurately engineering the desired atomic sites lead to challenges in making direct comparisons between experimental and theoretical results. In MoS2, the Mo-edge has been demonstrated to be active for HER whereas the S-edge is inert. Using a computational descriptor-based approach, we predict that by incorporating transition metal atoms (Fe, Co, Ni, or Cu) the S-edge site should also become HER active. Vertically standing, edge-terminated MoS2 nanofilms provide a well-defined model system for verifying these predictions. The transition metal doped MoS2 nanofilms show an increase in exchange current densities by at least two-fold, in agreement with the theoretical calculations. This work opens up further opportunities for improving electrochemical catalysts by incorporating promoters into particular atomic sites, and for using well-defined systems in order to understand the origin of the promotion effects.

Recent progresses in catalytic tar elimination during biomass gasification or pyrolysis—A review

Abstract: Biomass gasification is an interesting technology in the future development of a worldwide sustainable energy system, which can help to decrease our current dependence on fossil fuels. Biomass gasification is a thermal process where solid fuel is converted into a useful gas using several gasifying agents such as air, and steam. The producer gas has a great number of applications. The most important is being combustion for power and heat generation as well as raw gas for production of fuels or chemicals. This review mainly presents the recent progresses on tar elimination during the biomass gasification. Then, novel non-catalytic absorption and adsorption methods of tar removal under ambient temperature conducted by our laboratory members were also explained. In our opinion, the tar removal can be conducted by combination of catalytic reforming in the gasifier and oil materials adsorption in the scrubber. Furthermore, the tar catalytic reforming is a most significant step during biomass gasification or pyrolysis. Thus, the development of reasonable catalysts for tar elimination has been faced with a significant challenge in current society.