Functionalization and Characterization of Carbon Nanohorns (CNHs) for Hydrotreating of Gas Oils

Improvement in the functionality of carbon nanohorns (CNHs), a novel carbon nanomaterial, for hydrotreating applications is investigated in the present work. The current work was carried out by using pristine CNHs synthesized by the submerged arc in liquid nitrogen and their corresponding physicochemical properties were investigated. The surface area, pore diameter and pore volume of the pristine CNHs are 129 m²/g, 23.1 nm, and 0.64 cm³/g respectively. Functionalizing the CNHs with 30 wt% HNO₃ under reflux for 15 min to 4 h at 110 °C modified the physical and chemical properties. 30 min functionalization duration was found to be the best and a co-impregnation method was used to load Ni (2.5 wt%) and Mo (13 wt%) onto the support. Techniques used to thoroughly characterize the properties of pristine CNHs, functionalized CNHs and NiMo/CNHs catalyst include: Brauner-Emmett-Teller (BET), Fourier Transform Infrared (FTIR) and Raman Spectroscopy. Type II isotherm and mesoporous pore diameter was observed for CNHs in it’s pristine, functionalized or catalyst form. An increase in surface area of over 500 m²/g was also attained under optimum functionalized conditions. The pore volume of acid treated CNH samples for hydrotreating increased by ~10 % as compared to the pore volume of the pristine CNHs. FTIR results revealed the presence of carboxylic acid (–COOH) groups on the functionalized CNHs and I _D/I _G ratios from Raman spectroscopy was used to assess the increase in defects (nanowindow) on functionalized CNHs. The enhanced properties of functionalized and catalyst-supported CNHs offers prospect for hydrotreating gas oils.     

Hydrotreating of gas oil on SBA-15 supported NiMo catalysts

The siliceous and the metal substituted (B or Al)-SBA-15 molecular sieves were used as a support for NiMo hydrotreating catalysts (12 wt.% Mo and 2.4 wt.% Ni). The supports were characterized by X-ray diffraction (XRD), scanning electron microscopy and N₂ adsorption–desorption isotherms. The SBA-15 supported NiMo catalysts in oxide state were characterized by BET surface area analysis and XRD. The sulfided NiMo/SBA-15 catalysts were examined by DRIFT of CO adsorption and TPD of NH₃. The HDN and HDS activities with bitumen derived light gas oil at industrial conditions showed that Al substituted SBA-15 (Al-SBA-15) is the best among the supports studied for NiMo catalyst. A series of NiMo catalysts containing 7–22 wt.% Mo with Ni/Mo weight ratio of 0.2 was prepared using Al-SBA-15 support and characterized by BET surface area analysis, XRD and temperature programmed reduction and DRIFT spectroscopy of adsorbed CO. The DRIFT spectra of adsorbed CO showed the presence of both unpromoted and Ni promoted MoS₂ sites in all the catalysts, and maximum “NiMoS” sites concentration with 17 wt.% of Mo loading. The HDN and HDS activities of NiMo/Al-SBA-15 catalysts were studied using light gas oil at temperature, pressure and WHSV of 370 °C, 1300 psig and 4.5 h⁻¹, respectively. The NiMo/Al-SBA-15 catalyst with 17 wt.% Mo and 3.4 wt.% of Ni is found to be the best catalyst. The HDN and HDS activities of this catalyst are comparable with the conventional Al₂O₃ supported NiMo catalyst in real feed at industrial conditions.     

A comparative study on the effect of promoter content of hydrodesulfurization catalysts at different evaluation scales

CoMo and NiMo supported Al₂O₃ catalysts have been investigated for hydrotreating of model molecule as well as industrial feedstock. Activity studies were carried out for thiophene and SRGO hydrodesulfurization (HDS) in an atmospheric pressure and batch reactor respectively. These activities on sulfided catalysts were evaluated as a function of promoter content [M/(M + Mo) = 0.30, 0.34, 0.39; M = Co or Ni] using fixed (ca. 8 wt.%) molybdenum content. The promoted catalysts were characterized by textural properties, XRD, and temperature programmed reduction (TPR). TPR spectra of the Co and Ni promoter catalysts showed that Ni promotes the easy reduction of Mo species compared with Co. With the variation of promoter content NiMo catalyst was found to be superior to CoMo catalyst for gas oil HDS, while at low-promoter content the opposite trend was observed for HDS of thiophene. The behavior was attributed to the several reaction mechanisms involved for gas oil HDS. A nice relationship was obtained for hydrodesulfurized gas oil refractive index (RI) and aromatic content, which corresponds to the Ni hydrogenation property.     

Catalytic coprocessing of LDPE with coal and petroleum resid using different catalysts

Catalytic coprocessing of low density polyethylene (LDPE) with coal and heavy petroleum resid was investigated using four different catalysts that included both hydrotreating and hydrocracking catalysts. Reaction systems that were evaluated included LDPE alone; LDPE with coal; and LDPE, coal, and resid. The catalysts used were NiMo/Al₂O₃, a hydrotreating catalyst with some hydrocracking activity, and the hydrocracking catalysts Zeolyst 753, NiMo/zeolite, and HZSM-5. These catalysts were reacted individually or in combinations of 10 wt.% of each hydrocracking catalyst in NiMo/Al₂O₃. The catalytic reactions were performed at two temperatures, 400 and 430°C, using 1 wt.% of each catalyst or a combination of catalysts on a total feed basis. The effects of the different catalysts on the reaction products were measured in terms of solvent fractionation and total boiling point distribution. Reactions at the higher reaction temperature of 430°C resulted in substantially higher conversion and production of lighter products than the reactions at 400°C. The LDPE reaction system was sensitive to the catalyst type, and yielded increased conversion and lighter products when Zeolyst 753 and NiMo/zeolite were used. By contrast, the conversion and product slate obtained from the LDPE and coal systems were low and showed no effect due to the different types of catalyst. Introduction of resid to the LDPE/coal system increased the reactivity of the system and allowed the catalysts to have a larger effect. The hydrocracking catalysts were the most active in producing more conversion and hexane soluble material. Comparison of the effect of increasing the reaction time up to 5 h with 1 wt.% catalyst loading to the effect of increasing the catalyst loading from 1 wt.% to 10 wt.% for a reaction time of 1 h showed that increased reaction time was much more effective than catalyst loading in converting the solid LDPE to liquid reaction products.     

Effect of potential cycling on structure and activity of Pt nanoparticles dispersed on different carbon supports

Platinum particles synthesized via the Bönnemann methods were dispersed on two different Vulcan XC72 carbon supports. One was used after thermal treatment at 400 °C under nitrogen atmosphere, the other after oxidation of its surface by acid leaching using diluted HNO₃ in water (1/3). Characterization of the carbon support indicated that HNO₃ treatment leads to the decrease of the BET surface and to the increase of the surface acidity of the carbon support. After dispersion of the platinum catalyst, TEM results indicated that the mean particle size was a little higher on the non-oxidized support (Pt/XC72) than that on the functionalized one (Pt/XC72_HNO3), being 2.5 and 2.0 nm, respectively. However, potential cycles from 0.05 to 1.25 V vs. RHE led to a higher increase of the particle size when catalyst is dispersed on the functionalized support, reaching after 400 potential cycles 5.5 nm against 4.0 nm with the non-functionalized one. The effect of the upper limit (1.0 and 1.25 V vs. RHE) of the potential cycles on the active surface area and on the activity towards the oxygen reduction reaction (orr) was determined for both catalysts. Results indicated that the particle growth was not the main degradation process over the whole duration of the electrochemical experiments, but that dissolution/redeposition (Otswald ripening) was also involved. The predominant role of each degradation process depends on the number of cycles, on the upper potential limit and on the carbon surface state, and could be temporally separated. However, the lower activity towards orr was recorded for the (Pt/XC72_HNO3) cycled up to 1.0 V vs. RHE.     

The role of nickel in pyridine hydrodenitrogenation over NiMo/Al2O3

Al₂O₃ supported Mo, Ni, and NiMo/Al₂O₃ catalysts with various Ni contents were prepared to investigate the role of Ni as a promoter in a NiMo bimetallic catalyst system. The hydrodenitrogenation (HDN) reaction of pyridine as a catalytic probe was conducted over these catalysts under the same reaction conditions and the catalysts were characterized using BET surface area measurement, infrared spectroscopy, temperature programmed reduction, DRS and ESR. According to the results of reaction experiments, the NiMo/Al₂O₃ catalyst showed higher activity than Mo/Al₂O₃ catalyst in the HDN reaction and particularly the one with atomic ratio [Ni/(Ni+Mo)]=0.3 showed the best activity for the HDN of pyridine. The findings of this study lead us to suggest that the enhancement in the HDN activity with nickel addition could be attributed to the improvement in the reducibility of molybdenum and the formation of Ni-Mo-O phase.     

Effect of pre-treatment approach of a carbon support on activity of PtSn/C electrocatalysts for direct ethanol fuel cells

Vulcan XC-72R carbon was pretreated using acid and thermal activation methods, and the carbons obtained were used as supports for a PtSn/C catalyst synthesized by a successive reduction process. Surface characteristics of the supports, including BET surface area, pH_PZC and functional group, were analyzed using physical N₂ adsorption, mass titration, acid–base titration, and Fourier transform infrared (FTIR) spectrometer technique, respectively. The prepared PtSn/C catalysts were characterized by X-ray diffractometer (XRD), energy dispersive X-ray spectrometer (EDX), inductively coupled plasma–atomic emission spectrometry (ICP–AES), and transmission electron microscope (TEM) techniques, and then were examined for their behavior under ethanol oxidation as well as for their performance in a direct ethanol fuel cell (DEFC). The results showed that pretreatment by HNO₃ produced various oxygenated functional groups on the support surface and increased its acidic property. The strong acidity of the acid-treated support led to an unfavorable condition for the Pt reduction reaction and resulted in low Pt content but high Pt:Sn ratio in the PtSn/C catalyst. On the other hand, thermal activation increased the base functional groups on the carbon surface, which enhanced reduction of Pt precursor, and consequently, provided a small average metal particle size of 2.2 nm. The results from cyclic voltammetry, chronoamperometry and cell performance testing confirmed that the catalytic activity for ethanol oxidation and the performance in the direct ethanol fuel cell of the heat-treated carbon-supported PtSn catalyst was superior to the fresh PtSn/C catalyst and the acid-treated carbon-supported PtSn catalyst.     

Spherical mesocellular silica foams: a superior support for hydrodesulfurization of fluid catalytic cracking diesel

High surface area aluminum containing spherical mesocellular silica foams (SMCFs) with ultra-large pore volume and 3D pore size were successfully synthesized through a simple hydrothermal route, and the as-synthesized aluminum containing SMCFs (Al-SMCFs) was applied as the support of NiMo-base catalyst for the hydrodesulfurization (HDS) of fluid catalytic cracking (FCC) diesel. The as-synthesized supports and corresponding catalysts were characterized by powder small X-ray diffraction, nitrogen physisorption, scanning electron microscopy, transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy, and temperature-programmed reduction with H₂. The characterization results showed that, compared with other prepared catalysts (NiMo/Al-SBA-15 and NiMo/Al-KIT-6), the NiMo/Al-SMCFs catalyst possessed the most optimal physicochemical parameters, i.e., ultra-large 3D pore size (42.0 nm), high surface area (330.1 m²·g^?1), and ultra-large pore volume (1.96 cm³·g^?1), resulting in the formation of more homogeneous distribution of octahedral Mo active species and good mass transfer performance. Consequently, the NiMo/Al-SMCFs catalyst displayed the outstanding HDS performance (98.8%) of FCC diesel, confirming that the Al-SMCFs may be a type of promising candidate for oil hydrotreating.     

Preparation and catalytic performance of modified kaolin clay with big pore for the hydrodesulfurization of diesel

A kind of metakaolin materials with big pores was prepared from natural kaolin clays. The prepared metakaolin was introduced into alumina as composite support for hydrotreating application. A series of nickel–tungsten catalysts (NiO 2.9 wt%, WO₃ 27.2 wt%) supported on alumina-metakaolin, alumina-titania and bare alumina also were prepared. Electron microprobe analysis including SEM and TEM, BET and temperature programmed desorption of NH₃ were used for the samples characterization. Their hydrodesulfurization (HDS) activity for diesel were evaluated and compared. The results showed that NiW/alumina-metakaolin had excellent HDS activity and alumina-metakaolin support could be a good candidate support for hydrotreating catalysts.     

Effect of surface acid groups associated with amorphous and structured carbon on the catalytic hydrodechlorination of chlorobenzenes

BACKGROUND: Catalytic hydrodechlorination (HDC) is a progressive approach to treating chlorinated waste streams. While carbon is widely used as a catalyst support, the influence of carbon surface functionality on HDC performance has not been established. This work sets out to assess the impact of surface acid groups associated with activated carbon (AC), graphite and graphitic nanofibers (GNF) on Pd promoted gas phase HDC of chlorobenzene (CB) and 1,3‐dichlorobenzene (DCB). RESULTS: The acid groups were introduced by HNO₃ washing and the HDC reaction performed over bulk Pd and Pd physically mixed with each carbon. The carbon was subjected to a thermal treatment to remove the surface acidity. Characterization was by temperature programmed decomposition (TPD), temperature programmed hydrogen treatment (TPH), BET area, acid‐base titration, scanning and transmission electron microscopy. TPD, TPH and titration analyses served to establish the presence of surface oxygen groups after acid washing and facilitated an evaluation of the effectiveness of the thermal treatment to remove these groups. CONCLUSIONS: The surface acid groups inhibited HDC activity, a response most pronounced for Pd + AC, less so for Pd + graphite, while the effect was slight for Pd + GNF. HDC inhibition is attributed to chloroarene interaction with the surface functional (notably carboxylic) groups that impedes HDC. Fractional dechlorination of DCB was equivalent to or lower than CB HDC; there is some evidence of DCB interactions with heat treated graphite and GNF that served to raise HDC activity. Effective HDC over carbon based catalysts requires removal of surface acid groups. Copyright © 2008 Society of Chemical Industry     

NiMo Supported on Faujasite‐modified Al2O3 as Catalysts for the Hydrotreatment of a Light Cycle Oil/Straight Run Gas Oil Mixture

A study on the hydrotreating performance of sulfided NiMo supported in NH4⁺Y‐ and H⁺Y‐modified Al₂O₃ is reported. The effect of the addition of the corresponding NiMo‐exchanged zeolites was also investigated. The materials were characterized (by N₂ physisorption and surface acidity measurements) and evaluated in the upgrading of a middle distillates (LCO‐SRGO) mixture under industrial conditions. The main effects of the integration of the NiMo‐exchanged zeolite (from the NH⁴⁺‐faujasite) were an improvement of textural properties and the creation of strong surface Lewis sites. The corresponding sulfided formulations showed higher hydrodesulfurization and hydrodearomatization activities than the catalyst prepared from the protonic zeolite.     

Comparison of product selectivity during hydroprocessing of bitumen derived gas oil in the presence of NiMo/Al2O3 catalyst containing boron and phosphorus

A detailed experimental study was performed in a trickle-bed reactor using bitumen derived gas oil. The objective of this work was to compare the activity of NiMo/Al₂O₃ catalyst containing boron or phosphorus for the hydrotreating and mild hydrocracking of bitumen derived gas oil. Experiments were performed at the temperature and LHSV of 340-420 °C and 0.5-2 h⁻¹, respectively, using NiMo/Al₂O₃ catalysts containing 1.7 wt% boron or 2.7 wt% phosphorus. In the temperature range of 340-390 °C, higher nitrogen conversion was observed from boron containing catalyst than that from phosphorus containing catalyst whereas in the same temperature range, phosphorus containing catalyst gave higher relative removal of sulfur than boron containing catalyst. Phosphorus containing catalyst showed excellent hydrocracking and mild hydrocracking activities at all operating conditions. Higher naphtha yield and selectivity were obtained using phosphorus containing catalyst at all operating conditions. Maximum gasoline selectivity of ∼45 wt% was obtained at the temperature, pressure, and LHSV of 400 °C, 9.4 MPa and 0.5 h⁻¹, respectively, using catalyst containing 2.7 wt% phosphorus.     

Removal of Cu (II) from water pollutant with Tunisian activated lignin prepared by phosphoric acid activation

Activated lignin with a relative high BET surface area and a well-developed porosity has been prepared from Tunisian deposit lignin, by H₃PO₄ activation at various process conditions. Physical and chemical properties of activated carbons produced, implying BET surface area, Boehm titration, Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA), were investigated. It was found that the maximum surface area reached at the carbonization temperature of 500 °C in H₃PO₄ activation, and that the activated lignin prepared from lignin acidic activation, showed a surface area of 463 m²/g. The potential application of these carbons for the removal of heavy metal contaminant, has been investigated by measuring their adsorption capacities for Cu (II) as representative of main local toxic contaminant found in industrial wastewaters. The results obtained compare well and even favourably with those reported in literature for other unconventional materials.     

Surface characterization of Al2O3–SiO2 supported NiMo catalysts: An effect of support composition

Al₂O₃–SiO₂ mixed oxide has been investigated as a support for hydrotreating catalyst with variation of its composition [Si/(Si + Al) = 0.06, 0.12, 0.31, 0.56, 0.78] and its interaction with the surface active metals (NiMo). The composition of support and surface species (NiMo) of catalysts were characterized by specific surface area, atomic absorption, SEM-EDX, XRD, temperature programmed reduction (TPR), Raman analysis, scanning electron microscopy (STEM) and transmission electron microscopy (TEM). Incorporation of SiO₂ in Al₂O₃ promotes a weak interaction between the active phases and particularly catalyst that predominated with SiO₂ content. The oxide and sulfided catalysts characterization indicated that the effect of support is responsible to form different catalytic sites. Crystallization of MoO₃ phases and a relatively longer crystal of MoS₂ in the sulfided catalyst were attributed to an increasing SiO₂ content in the support. The catalytic behavior of the NiMo supported catalysts is explained in terms of structural changes on the surface due to the support and active metal interactions. The activity of the different catalysts evaluated in the thiophene hydrodesulfurization reaction was higher for the catalyst having lower SiO₂ content in the support.     

Standardization of the Boehm titration. Part I. CO2 expulsion and endpoint determination

The various steps required in the Boehm titration (CO₂ removal, agitation method, endpoint determination, etc.) are carried out in different ways by different research groups, making a comparison of the results between these groups difficult. Herein, the methods of CO₂ expulsion and endpoint determination for the Boehm titration were standardized. Blank samples of the three Boehm reaction bases, NaHCO₃, Na₂CO₃ and NaOH, were examined for complete CO₂ expulsion through sparging with an inert gas (N₂ or Ar), heating, or utilizing a N₂-filled glove box. Boehm titrations using NaOH as the reaction base were studied through direct titration and back-titration. It was found that to minimize errors both the NaOH titrant and HCl should be standardized prior to titration and that a back-titration is preferable for all three reaction bases. Additionally, the titration should be performed immediately after degassing for 2 h with N₂ or Ar, and degassing should continue during the titration. This is found to be particularly true of the NaOH reaction base, where the effects of dissolved CO₂ are the most noticeable and persistent. With sufficient CO₂ removal, there is no significant difference between pH electrode or colour indication endpoint determination, and either is satisfactory.     

Synergistic effect of Pt or Pd and perovskite oxide for water gas shift reaction

The water gas shift (WGS) reaction over Pt and Pd catalysts supported on various perovskite oxides has been investigated at 573 K without catalyst pretreatment. The Pt and Pd catalysts on LaCoO₃ support showed high catalytic activity. Interaction between Pt or Pd and the support is considered to promote the WGS reaction: Pt/LaCoO₃ had high initial activity but deactivated immediately; Pd/LaCoO₃ was less active than Pt/LaCoO₃, but had superior stability. Catalysts were characterized using XRD, STEM, XPS, and H₂-temperature programmed reduction (TPR). Results of this study showed that reduction of the support decreased the CO conversion on Pt/LaCoO₃. On the other hand, Pd/LaCoO₃ showed stable activity for the WGS reaction. Therefore, Pd was added to Pt/LaCoO₃ for stabilizing the catalyst activity, and 0.5 wt.% Pd/1 wt.% Pt/LaCoO₃ catalyst showed higher activity and stability.     

Effect of supercritical deposition synthesis on dibenzothiophene hydrodesulfurization over NiMo/Al2O3 nanocatalyst

The synthesis of two NiMo/Al₂O₃ catalysts by the supercritical carbon dioxide/methanol deposition (NiMo‐SCF) and the conventional method of wet coimpregnation (NiMo‐IMP) were conducted. The results of the physical and chemical characterization techniques (adsorption–desorption of nitrogen, oxygen chemisorption, XRD, TPR, TEM, and EDAX) for the NiMo‐SCF and NiMo‐IMP demonstrated high and uniform dispersed deposition of Ni and Mo on the Al₂O₃ support for the newly developed catalyst. The hydrodesulfurization (HDS) of fuel model compound, dibenzothiophene, was used in the evaluation of the NiMo‐SCF catalyst vs. the commercial catalyst (NiMo‐COM). Higher conversion for the NiMo‐SCF catalyst was obtained. The kinetic analysis of the reaction data was carried out to calculate the reaction rate constant of the synthesized and commercial catalysts in the temperature rang of 543–603 K. Analysis of the experimental data using Arrhenius' law resulted in the calculation of frequency factor and activation energy of the HDS for the two catalysts. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Two-stage coal liquefaction using sequential mineral and hydrotreating catalysts

Two-stage coal liquefaction offers significant improvements over single-stage processing in terms of product yields. The proposed two-stage operation utilizes an inexpensive and readily available mineral or disposable catalyst in the first stage followed by a commercial hydrotreating catalyst in the second stage. Single stage processing at 450°C and 425°C both show metal sulfides, i.e. pyrite, to be effective in increasing oil yields. In two-stage processing at 450°/410°C the sequence of pyrite followed by NiMo/Al₂O₃ is the most effective combination for producing oil (pentane soluble materials). Two stage processing at 425°/425°C utilizing sulfided liquefaction residue ash or pyrite as first-stage catalysts yields the highest percentage of oil. The improvements shown by solubility product distributions are verified by distillation curves of the reaction product. Evidence of pore diffusion limitation is apparent in the pelletized NiMo/Al₂O₃. Changes in catalyst morphology may be necessary to achieve maximum yields.     

Co-hydrotreating light cycle oil-canola oil blends

Canola oil and light cycle oil (LCO) blends were co-hydrotreated over a commercial hydrotreating catalyst (NiMo/Al₂O₃) to produce diesel fuel with a green diesel component. High hydrodeoxygenation, hydrodesulphurization and hydrodenitrogenation catalytic activities were achieved for all three feedstocks tested in the temperature range of 350–380 °C with a hydrogen pressure of 7 MPa and a gas/oil ratio of 800 nL/L. The hydrocracking conversion of the 360 °C + materials in the feedstocks increased by 5% and 15% when 5 and 7.5 wt-% canola oil was added to the LCO, respectively. Compared to the pure LCO, the cetane index of the diesel product formed from hydrotreating the two canola oil-LCO blends increased by 2.5 and 4, respectively. Due to the higher hydrogen requirement to crack and deoxygenate the triglycerides contained in the canola oil, a higher hydrogen consumption was needed to hydrotreat the canola oil-LCO blends.

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Immobilization of Metalloporphyrin on Functionalized Magnetic Nanoparticles as a Catalyst in Oxidation of Cyclohexene: Novel Modified Fe3O4 Nanoparticles with Triethoxysilane Agent

Magnetic nanoparticles, Fe₃O₄, have been prepared and functionalized by (N-(3-(triethoxysilyl)propyl)isonicotinamide) and characterized by infrared spectroscopy, thermal analysis (TGA/DTA), X-ray powder diffraction, scanning electron microscopy, elemental analysis and BET surface area measurement. The functionalized Fe₃O₄ nanoparticles were used as a support to anchor metalloporphyrin. Application of immobilized metalloporphyrin as a heterogeneous catalyst in the oxidation of cyclohexene was explored. Effect of various parameters such as solvent and temperature on immobilization process and also various parameters (solvent, time, oxidant and axial group effect) on oxidation of cyclohexene has been investigated. The result showed that the immobilized metalloporphyrin on functionalized magnetic nanoparticles is an efficient and reusable catalyst for oxidation of cyclohexene.