Lower Coke Deposition Research Articles

Effect of Ce addition on the surface properties and n-dodecane dehydrogenation performance of Pt-Sn/Ce-Al2O3 catalyst

Ce-modified alumina carriers with different Ce content were prepared by vacuum isovolume impregnation method aiming to improve the n-dodecane catalytic dehydrogenation performance of PtSn/Al2O3 catalyst. The support and catalyst were characterized by XRD, N2 adsorption-desorption, NH3-TPD, H2-TPR, CO-pulse adsorption and TG-DTG. Results showed that Ce addition decreased the surface acid amount significantly and inhibited the reduction of SnO x species. Besides, Ce containing catalyst showed higher n-dodecane dehydrogenation activity and stability and lower coke deposition amount and coke burning temperature. In our study, the optimal Ce addition amount for n-dodecane dehydrogenation was 2%.

Sustainable production of aromatics from bio-oils through combined catalytic upgrading with in situ generated hydrogen

Pyrolysis liquids or bio-oils from rice husks are selectively converted into aromatics through a combined catalytic process, which includes two sequent steps: reforming and upgrading. Hydrogen from methanol and low-weight molecules in bio-oil is in situ generated in the reforming reactor. Methanol (16wt% of total bio-oils) is added not only as the hydrogen donor, but also as polar solvent for homogenizing bio-oil and reducing its viscosity. Structured nickel nets are used as both the reforming catalyst and heating grid for gasifying high-boiling-point components of bio-oil. In the upgrading reactor, the combination of Co–Ru–Zr/silica with Pt-ZSM-5 gives the highest yield of aromatics (53.7%) and the lowest coke deposition (7.1%). Hydrogen for deoxygenation is generated from reforming of added methanol and low-weight molecules in bio-oil. Coke formation during fixed-bed upgrading can be significantly suppressed through the combined catalytic process.

Hydrogen from synthetic biogas by catalyzed MDR and SIP: Screening of catalyst and iron oxide mixtures

Hydrogen production plus purification has been studied by the joint use of methane dry reforming (MDR) and the reduction–oxidation of iron oxides (Steam-Iron Process or SIP) within the same reactor. The raw material studied has been an equimolar mixture of CH4 and CO2 simulating the composition of a biogas exempt of any other contaminant. The study has been mainly carried out by thermogravimetry, using mixtures of a catalyst and a doped iron oxide both synthesized in laboratory. The catalyst has been based in a nickel aluminate with nickel oxide in excess above its stoichiometric composition. The iron oxide indirectly “stores” the hydrogen produced by MDR by becoming into its metallic state during the reduction step. This hydrogen is released later on during the oxidation step of the metal with steam. On this way, dry reforming reaction is displaced towards products (H2 and CO) which are consumed “on site” by the oxide. This cyclic process has demonstrated that the key issue to achieve the goal of hydrogen purity enough to be consumed in a PEMFC, is producing a metallic iron with low coke deposition and an acceptable inert role. The nature of the coke and the way in which it is deposited, have also been studied in this work.

Studies of the preparation method of ceria-promoted nickel catalyst for carbon dioxide reforming of methane

The CO2 reforming reactions of methane were carried out using an alumina-supported nickel catalyst. In order to reduce the coke deposition, the preparation methods of the ceria-promoted nickel catalysts were investigated. The physical mixing of CeO2 realized a 50% reduction in the deposited coke per 1mol of produced CO compared to the catalyst without CeO2. Meanwhile, the catalyst prepared by the impregnation of nickel aluminate with a cerium nitrate solution followed by reduction under a hydrogen stream showed the lowest coke deposition activity. Particularly, the use of alumina prepared by the alkoxide method gave a 5.8% deposited coke produced by the catalyst without CeO2. This type of nickel catalyst showed a high reforming activity without deactivation and a low coke deposition activity.

Hydrocracking of Maya Vacuum Residue with NiMo Catalysts Supported on Mesoporous Alumina and Silica–Alumina

Hydrocracking of heavy oils poses greater challenges than that of lighter feeds in terms of catalyst properties and resistance to deactivation. The development of larger pore size catalysts may be beneficial to improve their effectiveness toward cracking the larger molecules present in these feedstocks. Mesoporous alumina and mesoporous silica–alumina (MSA) with different textural properties were used as supports to prepare NiMo-based catalysts. These catalysts were tested in the hydrocracking of a vacuum residue (VR) from Maya crude oil and compared against a commercial Al2O3 catalyst. The conversion of VR and asphaltenes into lighter hydrocarbons obtained with supports and catalysts was determined, and the coke deposition process was studied. The in-house developed catalysts were utilized for two consecutive runs with fresh feed to evaluate coke deposition during reutilization of the materials. It was found that coke deposition occurred mainly in the first run, with carbonaceous deposits stabilizing for all the catalysts during their reutilization. Reaction temperature had an important impact on conversions and product distributions, with higher reaction temperatures accounting for higher VR and asphaltene conversions at the expense of a large increase in gas yields. Although the NiMo/Al2O3 catalyst achieved similar VR conversion to the other catalysts, it displayed higher asphaltene conversion with lower coke deposition and a reduced gas yield. The effectiveness of this catalyst can be attributed to its larger pores that can allow better diffusion of asphaltene molecules than MSA or NiMo/MSA as well as the commercial catalyst.

Effect of support surface on methane dry-reforming catalyst preparation

Present investigation shows the different catalytic behavior of Ni-supported catalysts in the dry-reforming of methane. Highly ordered Silicalite-1, highly defective pure silica MCM-41 and pure silica delaminated zeolite ITQ-6 have been prepared and used as support for nickel deposition.The heterogeneity of the support surface strongly affects the nickel particles deposition. Delaminated surface of ITQ-6 material permits to obtain high nickel particles dispersion and high metal sintering resistance. The particles of Ni remain free from coke formation since they are very well dispersed and strongly linked to the support.Good overall catalytic performances was achieved by Ni-ITQ-6 catalyst, after 30h of reaction: ≅80% of CH4 conversion, ≅90% of CO2 conversion, H2/CO molar ratio >1.3 and very low coke deposition, <4wt.%.

Catalytic Steam Gasification of Biomass for a Sustainable Hydrogen Future: Influence of Catalyst Composition

Hydrogen is regarded as a clean energy for fuelling the future. Hydrogen will be the energy carrier from other resources such as hydropower, wind, solar and biomass. Producing hydrogen from gasification of biomass wastes, particularly in the presence of steam, represents a promising route to produce this clean and CO2-neutral fuel. The steam pyrolysis–gasification of biomass (wood sawdust) was carried out with various nickel-based catalysts for hydrogen production in a two-stage fixed bed reaction system. The wood sawdust was pyrolysed in the first reactor and the derived products were gasified in the second reactor in the presence of the catalyst and steam. The synthesised Ni–Ca–Al and Ni–Zn–Al catalysts were prepared by co-precipitation method with different Ni loadings of 20 mol% and various Zn/Al or Ca/Al ratios, which were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). The results showed that the Ni/Zn–Al (1:9) catalyst resulted in higher hydrogen production (23.9 mmol H2 g−1 biomass) compared with the Ni/Ca–Al (1:9) catalyst (12.7 23.9 mmol H2 g−1 biomass) and in addition, the increase of Ca or Zn content in the catalyst slightly increased the hydrogen production. The TPO results showed that the catalyst suffered negligible coke deposition from the catalytic steam pyrolysis/gasification of wood sawdust. Additionally, Na2CO3 basic solution was also found to produce a catalyst with better performance and lower coke deposition, compared with NH4OH catalyst preparation agent, as observed by TPO, SEM and TEM analysis.

Activity and Stability of Zinc and Phosphorus Modified NiMo/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Catalyst for Residue Hydrodesulfurization

Conversion of heavy oil to added-value lighter fractions is very important. One conversion method is hydrotreatment of heavier residues in the hydroprocessing unit followed by cracking in the FCC or RFCC unit. However, if heavier residues are treated with the same catalyst under the same process conditions, the sulfur contents in the product oil will increase, so higher temperatures will be required to maintain constant sulfur in the product oil. This higher temperature also results in shorter catalyst life. This study developed zinc and phosphorus modified NiMo/Al2O3 catalyst which is resistant to deactivation by coke deposition. The effect of zinc on the suppression of deactivation rate was remarkable in the catalyst containing phosphorus in this study. IR spectroscopy showed that the coexistence of zinc with phosphorus inhibited the increase of acidic hydroxyls and the addition of phosphorus increased acidic alumina hydroxyls, leading to lower coke deposition on the zinc and phosphorus modified NiMo/Al2O3 catalyst. Zinc and phosphorus modified NiMo/Al2O3 catalyst also showed less deactivation and higher hydrodesulfurization activity in the middle period of the bench plant test. These results were well-consistent with catalyst performance in the commercial plant.

Effect of the introduction of niobium carbide on non-oxidative dehydro-aromatization of methane over MoMCM-22

The effect of the introduction of niobium carbide was studied on the dehydro-aromatization of methane over a molybdenum containing HMCM-22 zeolite at 973 K. The introduction of niobium decreased Bronsted acidity, affecting catalyst behavior on the dehydro-aromatization of methane. Niobium carbide containing zeolite showed lower activity, lower coke deposition and predominant formation of naphthalene, in the expenses of benzene, the major product observed for Mo containing zeolite. Besides carbidic carbon, two other types of coke were observed: one associated to molybdenum and the other associated to Bronsted acid sites located both on the catalyst surface and inside zeolite pores.

Hydrogen production from biomass gasification with Ni/MCM-41 catalysts: Influence of Ni content

The steam pyrolysis-gasification of biomass, wood sawdust, was carried out with a Ni/MCM-41 catalyst for hydrogen production in a two-stage fixed bed reaction system. The wood sawdust was pyrolysed in the first reactor and the derived products were gasified in the second reactor. The synthesised MCM-41 mesoporous catalyst supports were impregnated with different Ni loadings (5, 10, 20 and 40wt.%), which were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). NiO particles were homogeneously dispersed inside the pores of 5, 10, and 20wt.% Ni/MCM-41 catalysts; however, more bulkly NiO particles (up to 200nm particle size) were detected outside the pores with an increase of the Ni loading up to 40wt.%. Gas production was increased from 40.7 to 62.8wt.%, hydrogen production was increased from 30.1 to 50.6vol.% of total gas composition when the Ni loading was increased from 5 to 40wt.% during the pyrolysis-gasification of wood sawdust. This work showed low coke deposition (from 0.5 to 4.0wt.%) with valuable bio-oil by-products using the Ni/MCM-41 catalyst. The highly efficient conversion of renewable biomass resource to hydrogen and bio-oil with very low coke deposition indicates that biomass gasification on Ni/MCM-41 catalysts via two-stage reaction is a promising method for the development of the biorefinery concept.

Modifications of an HY zeolite for n-octane hydroconversion

Solids based on HY zeolite were modified by either dealuminization (D) followed by chemical vapour deposition of silicon (CVD). Additionally, impregnation of Pt or Ni was performed over selected D and CVD solids. Samples were characterized by XRD, 27Al and 29Si NMR, acidity measurements, N 2 adsorption/desorption isotherms, Raman analysis and evaluated in n-octane hydroconversion at P = 1 atm and T = 300 °C. In comparison with the CVD and pure D series of solids, Pt impregnation on dealuminated HY resulted in a high level of isomerization products. Although the conversion upon using Ni-containing dealuminated HY was elevated, cracking products were predominant over this solid. The trends in the activity can be explained by the accessibility of acidic sites and their acidity. The catalytic activity follows the order PtCVD1 > NiD > PtD ∼ D > CVD1. The combined effect of moderate acidity and Pt dispersion resulted in better catalytic performance for the PtCVD1 catalyst, which was active in the hydroisomerization reaction (conversion of 30%) with almost no coking on the sample, whereas cracking products were predominant over other solids. The characterization of spent catalysts showed no loss in activity, with low coke deposition on solid surface over the CVD1 sample in comparison with the D series of solids. Furthermore, mechanistic insights demonstrated that on PtCVD1, the adsorbed carbon species were formed via the cracking and oligomerization of n-octane precursors.

Hydrogen production from the pyrolysis–gasification of waste tyres with a nickel/cerium catalyst

Hydrogen production from the pyrolysis–gasification of waste tyres has been investigated with a Ni/CeO 2/Al 2O 3 catalyst using a two-stage fixed bed reaction system. The conditions of catalyst preparation such as Ni and CeO 2 content and calcination temperature were investigated in relation to product yield and composition. The fresh and reacted catalysts were analysed using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results showed that there were small changes in the gas and hydrogen yield by adding 5 wt.% of CeO 2 into the Ni/CeO 2/Al 2O 3 catalyst. The gas yield related to the mass of waste tyre and the amount of reacted water were increased with the increase of CeO 2 content from 5 to 15 wt.%. However, with the further increase of CeO 2 content to 30 wt.%, the gas yield related to the mass of tyre and the amount of reacted water was reduced. Increasing the Ni content of the catalyst showed a positive influence on the gas yield and hydrogen production. The investigation of the calcination temperature of the Ni/CeO 2/Al 2O 3 catalyst showed that the oil yield related to the mass of tyre and reacted water decreased from 28.4 to 23.4 wt.% for the catalyst calcined at 500 °C, and decreased from 24.2 to 17.7 wt.% for the catalyst calcined at 750 °C. When the Ni content of the catalyst was increased from 5 to 20 wt.%. there were only small changes in total gas and hydrogen production from the pyrolysis–gasification of waste tyre. Lower coke deposition on the reacted catalyst was obtained for the Ni/CeO 2/Al 2O 3 catalyst prepared at the calcination temperature of 750 °C compared with the 500 °C calcination temperature.

Investigation of the catalytic activity of Rh–LaCoO 3 catalyst in the conversion of tar from biomass devolatilization products

The catalytic activity in the conversion of biomass devolatilization products to syngas of a novel alumina supported Rh–LaCoO 3 catalyst has been investigated in a double fixed bed reactor system. A catalytic screening has been carried out in order to define the limits of both operation parameters and Rh load to obtain a complete tar conversion associated with the lowest coke deposition taking into account either efficiency or costs of the material. The effect of rhodium load has been investigated in the range 0.1–1 wt.%. The study of the operation parameters has been performed by modifying the reaction temperature (500–700 °C), the catalyst amount (0.25–1 g) and the N 2 flow rate (12–60 Nl h −1). The catalyst still provides good performances in tar and light hydrocarbons conversion when the temperature is lowered down to 600 °C. At 700 °C a complete tar conversion can be obtained both reducing the 1% Rh–LaCoO 3 catalyst amount in the reactor to 0.5 g and decreasing the Rh load down to 0.1 wt.%. TPR and DRIFT analyses have been performed to characterize the nature of Rh and to correlate this feature to the catalytic performances.

Promoting effect of small amount of Fe addition onto Co catalyst supported on α-Al 2O 3 for steam reforming of ethanol

We examined the promotion effect of loading small amounts of Fe onto various Co catalysts for steam reforming of ethanol. Among these catalysts, catalysts supported on SrTiO 3 and α-Al 2O 3 showed remarkable effects of iron loading onto cobalt catalyst. The Fe-loaded Co/α-Al 2O 3 showed higher yield of hydrogen, low coke deposition on the catalysts, and high activity for steam reforming of acetaldehyde, which was an intermediate of the steam reforming of ethanol. Characterization of the catalyst revealed that Fe and Co metal coexisted on the catalyst support. Synergetic effects of these two metals were observed.

Effect of Calcination Temperature on La-Modified Al2O3 Catalysts for Vapor Phase Hydrofluorination of Acetylene to Vinyl Fluoride

A La-modified Al2O3 catalyst was prepared with deposition-precipitation method. The effect of calcination temperature on the reactivity for vapor phase hydrofluorination of acetylene to vinyl fluoride. The catalysts calcined at different temperatures were characterized using NH3-TPD, pyridine-FTIR, X-ray diffraction, and Raman techniques. It was found that the calcination process could not only change the structure of these catalysts but also modify the amount of surface acidity on the catalysts. The catalyst calcined at 400 °C exhibited the highest conversion of acetylene (94.6%) and highest selectivity to vinyl fluoride (83.4%) and lower coke deposition selectivity (0.72%). The highest activity was related to the largest amount of surface acidity on the catalyst, and the coke deposition was also related to the total amount of surface acidic sites.

Catalytic Applications of oxalic acid treated CuO/HZSM-5 in Methanol Conversion to Hydrocarbons

A series ofCuO over HZSM-5 catalysts were prepared by wet impregnation technique followed by dealumination using oxalic acid. The loading ofCuO over HZSM-5 was kept between 0 and 9 wt% and treated with oxalic acid. XRD, Surface area analyzer, metal trace analyzer and SEM techniques were used to characterize the catalysts. The higher yield of gasoline range hydrocarbons were obtained with the increase in weight % ofCuO over HZSM-5.Effect of run time on the hydrocarbon yields and methanol conversion was investigated. The activity of the catalyst decreased progressively with time on stream. Relatively lower coke deposition over HZSM-5 catalysts was observed compared to CuO impregnated HZSM-5 catalyst. The effect of run time was studied to investigate the effect oxalic acid treatment on catalyst stability.

Investigations on the properties of ceria–zirconia-supported Ni and Rh catalysts and their performance in acetic acid steam reforming

The production of hydrogen via steam reforming of acetic acid was examined over Ni and Rh supported on a CeO 2–ZrO 2-mixed oxide. The catalysts were tested at 550–650–750 °C using steam/carbon = 3. Steam reforming, water gas shift, and decarboxylation are the main reactions taking place over the support alone. In parallel, dehydrogenation leads to the formation of carbon deposits on the surface of the mixed oxide. The addition of the metals enables the reforming reactions to proceed with high rates producing hydrogen yields close to thermodynamic equilibrium even at 650 °C. The oxygen exchange reactions are enhanced leading to much lower coke deposition. The nature of the metal affects not only the quantity but also the quality and the location of the carbon deposits, as evidenced from temperature-programing oxidation tests. The synergy of the support and metal is the key factor for the low coke deposition, which is even lower for the Rh catalyst.

Hybrid catalysts used in the Catalytic Steam Cracking process (CSC): Influence of the pore characteristics and the surface acidity properties of the ZSM-5 zeolite-based component on the overall catalytic performance

Data of the present work show that, in order to obtain high yields in light olefins, the ZSM-5 zeolite – the cracking component of the hybrid catalyst, must have a relatively low SiO 2/Al 2O 3 mol ratio, so that its density of acid sites is high, thus resulting in a high total conversion. Such zeolite must also exhibit relatively mild acidity strength, favouring thus a high propylene/ethylene product ratio. On the other hand, these milder acid sites also lead to a lower coke deposition and thus to a greater on-stream catalyst stability because the cleaning action of the hydrogen spilt-over species is much eased. Feed contamination by trimethylbenzenes is an excellent tool for providing further evidence of the coke cleaning effect by the hydrogen spilt-over species, the latter being generated by the Ni supported co-catalyst. In the case of blending of petroleum hydrocarbon feedstocks with non-oil derived compounds, the latter should not have strong competitive adsorption properties such as those found in polymethylbenzenes (ex: 1,3,5-trimethylbenzene), otherwise rapid fouling phenomena may occur.

Ethanol steam reforming on Mg- and Ca-modified Cu–Ni/SBA-15 catalysts

The effect of Mg and Ca incorporation (0–20 wt%) into CuNi/SBA-15 catalysts for hydrogen production by ethanol steam reforming has been studied. Promoting elements, Ca and Mg, were added to SBA-15 support prior to the active phase, Cu (2 wt%) and Ni (7 wt%). In both cases, the metals were incorporated to SBA-15 by incipient wetness impregnation followed by calcination to obtain the corresponding oxides. XRD analyses and TEM images demonstrated that CaO and MgO improved the dispersion of the Cu–Ni phase. Moreover, TPR profiles showed that Ca or Mg strengthened the interaction between the SBA-15 support and the Cu–Ni phase. Both promoting effects of Ca and Mg, together with their basic character enhanced the catalytic performance of CuNi/SBA-15 catalysts on ethanol steam reforming, giving higher hydrogen selectivity and lower coke deposition.

Ethanol steam reforming over Rh/CexZr1−xO2 catalysts: Impact of the CO–CO2–CH4 interconversion reactions on the H2 production

CexZr1−xO2 mixed oxide-supported 1wt.%Rh catalysts were prepared by wet impregnation using Rh nitrate as a precursor and calcined at 900°C. They were characterized by BET surface area, XRD, CO2 chemisorption and H2 chemisorption at −85°C and tested in the ethanol steam reforming at 600°C under atmospheric pressure, with water to ethanol molar ratio equal to 4, without carrier gas. The best performances, i.e. the highest hydrogen yield and the lowest coke deposition, were obtained over Rh/Ce0.5Zr0.5O2, i.e. 3.63mol H2/molethanol. This catalyst was subsequently evaluated under various reaction conditions. Whatever the temperature and the water to ethanol ratio, the ethanol steam reforming yielded a large amount of methane, which tends to reduce the H2 production. To elucidate the origin of the methane production, CO/CO2/CH4 interconversion reactions were studied. It was shown that such catalyst favours the formation of methane via CO hydrogenation. The direct hydrogenation of CO2 was not observed. In parallel, the catalyst was active in the reverse water gas shift (RWGS) reaction between CO2 and H2, leading CO and H2O.