Low Space Velocity Research Articles

바나듐 계열 촉매를 통한 NOx의 NH3-SCR에 관한 실험적 연구

T heH 3-SCR characteristics of NOX over a V-based catalyst are experimentally examined over a wide range of operating conditions, i.e., 170-590°C and 30,000-50,000 h -1 , with a simulated diesel exhaust containing NH3, NO, NO2, O2, H2O, and N2. The influences of the space velocity and oxygen concentration on the standard-SCR reaction are analyzed, and it is shown that the low space velocity and high oxygen concentration promote the SCR activity by ammonia. The best deNOX efficiency is obtained with a NO2/NOX ratio of 0.5 because of an enhanced chemical activity induced by the fast-SCR reaction, while at the NO2/NOX ratios above 0.5 the deNOX activity decreases due to the slow-SCR reaction. The oxidation of ammonia begins to take place at about 300°C and the reaction products, such as N2, NO, NO2, N2O, and H2O, are produced by the undesirable oxidation reactions of ammonia, particularly at high temperatures above 450°C. Also, NO2 decomposes to NO and O2 at temperatures above 240°C. Therefore, NO2 decomposition and ammonia oxidation reactions deteriorate significantly the SCR catalytic activity at high temperatures.

Correlation patterns and effect of syngas conversion level for product selectivity to alcohols and hydrocarbons over molybdenum sulfide based catalysts

The focus of the present study was to investigate the effect of the operation conditions, space velocity and temperature, on product distribution for a K–Ni–MoS2 catalyst for mixed alcohol synthesis from syngas. All experiments were performed at 91bar pressure and constant H2/CO=1 syngas feed ratio. For comparison, results from a non-promoted MoS2 catalyst are presented. It was found that the CO conversion level for the K–Ni–MoS2 catalyst very much decides the alcohol and hydrocarbon selectivities. Increased CO conversion by means of increased temperature (tested between 330 and 370°C) or decreased space velocity (tested between 2400 and 18,000ml/(gcath)), both have the same effect on the product distribution with decreased alcohol selectivity and increased hydrocarbon selectivity. Increased CO conversion also leads to a greater long-to-short alcohol chain ratio. This indicates that shorter alcohols are building blocks for longer alcohols and that those alcohols can be converted to hydrocarbons by secondary reactions. At high temperature (370°C) and low space velocity (2400ml/(gcath)) the selectivity to isobutanol is much greater than previously reported (9%C). The promoted catalyst (K–Ni–MoS2) is also compared to a non-promoted (MoS2) catalyst; the promoted catalyst has quite high alcohol selectivity, while almost only hydrocarbons are produced with the non-promoted catalyst. Another essential difference between the two catalysts is that the paraffin to olefin ratio within the hydrocarbon group is significantly different. For the non-promoted catalyst virtually no olefins are produced, only paraffins, while the promoted catalyst produces approximately equal amounts of C2–C6 olefins and paraffins. Indications of olefins being produced by dehydration of alcohols were found. The selectivity to other non-alcohol oxygenates (mostly short esters and aldehydes) is between 5 and 10%C and varies little with space velocity but decreases slightly with increased temperature. Very strong correlation patterns (identical chain growth probability) and identical deviations under certain reaction conditions between aldehyde and alcohol selectivities (for the same carbon chain length) indicate that they derive from the same intermediate. Also olefin selectivity is correlated to alcohol selectivity, but the correlation is not as strong as between aldehydes and alcohols. The selectivity to an ester is correlated to the selectivity to the two corresponding alcohols, in the same way as an ester can be thought of as built from two alcohol chains put together (with some H2 removed). This means that, e.g. methyl acetate selectivity (C3) is correlated to the combination of methanol (C1) and ethanol (C2) selectivities.

Fischer-Tropsch Synthesis: Co turnover Frequency Rates over Co/Al2O3Catalysts with Different Reduction Promoters

Cobalt (Co) turnover frequency (TOF) has been reported to be independent of Co dispersion and support type. However, wide discrepancies in Co TOF values exist in the literature. Differences in catalyst preparation, process conditions, and characterization technique could be major factors that may account for the discrepancies. Therefore, a more accurate assessment of Co turnover frequency (TOF) is needed. In this study, Co TOFs over different Co/Al2O3 catalysts promoted with Pd, Ru, Pt and Re at the beginning of reaction and at steady state were determined. The catalysts were prepared in different batches, which resulted in two Co cluster sizes: small Co particle size (∼6 nm) and large Co particle size (11.5 nm). Fischer-Tropsch synthesis (FTS) reaction was carried out at different conditions in a continuous stirred tank reactor (CSTR). All promoted Co catalysts were characterized using BET, TPR, H2-chemisorption and pulse re-oxidation. The FTS was conducted at 220–230 °C, 1.5 MPa, 6–13 Nl/gcat/h and H2/CO = 2.1. Results indicate that catalyst preparation including promoter effect and process conditions significantly impact initial and steady state TOF values. The Co catalysts with larger particles had a larger Co TOF and low space velocity (SV) reduced the number of Co active sites due to severe catalyst deactivation at high CO conversion. For SV of 8.0–13.0 Nl/g-cat/h and 1.5 MPa, high Co TOF values (0.074–0.082 s−1, at 210 °C) over the Re and Pt promoted 25%Co/Al2O3 were achieved and were in good agreement with recently published value (0.073s−1) in a few literature. Moreover, these values are about two times the values (0.023–0.045 s−1) reported in some Co related literature under similar conditions. Therefore, true TOF on single Co cluster with the size of 11.5 nm at 210 °C and 1.5–2.0 MPa should be about 0.073–0.082 s−1 (this value is conversion dependent). The effect of promoters (Pd, Ru, Pt and Re) and process conditions on FTS activity and selectivities (hydrocarbons, watersoluble oxygenates and CO2) was also studied.

CO2 capture from the atmosphere and simultaneous concentration using zeolites and amine-grafted SBA-15.

CO(2) capture from the atmosphere and concentration by cyclic adsorption-desorption processes are studied for the first time. New high microporosity materials, zeolite types Li-LSX and K-LSX, are compared to zeolite NaX and amine-grafted SBA-15 with low amine content. Breakthrough performance showed low silica type X (LSX) to have the most promise for application in dry conditions and capable of high space velocities of at least 63,000 h(-1), with minimal spreading of the CO(2) breakthrough curve. Amine-grafted silica was the only adsorbent able to operate in wet conditions, but at a lower space velocity of 1500 h(-1), due to slower uptake rates. The results illustrate that the uptake rate is as important as the equilibrium adsorbed amount in determining the cyclic process performance. Li-LSX was found to have double the capacity of zeolite NaX at atmospheric conditions, also higher than all other reported zeolites. It is further demonstrated that by using a combined temperature and vacuum swing cycle, the CO(2) concentration in the desorption product is >90% for all adsorbents in pellet form. This is the first report of such high CO(2) product concentrations from a single cycle, using atmospheric air.

The influence of sulfur dioxide and water on the performance of a marine SCR catalyst

This study investigates how sulfur affects the NOx reduction activity over a commercial vanadium based urea-SCR catalyst for marine applications, especially at low temperatures, and in combination with H2O. The addition of SO2 in the absence of H2O promotes the NOx reduction at 350°C, while the addition of H2O, in the absence of SO2, gives rise to a decrease in the NOx reduction and also an inhibition of the N2O formation. The same trends are observed at transient temperatures, but no promotional effect by SO2 is seen at temperatures below 230°C. Further, long term effects of SO2 and H2O were investigated and the NOx reduction remains stable, also after long term exposure of SO2. The ammonia desorption is investigated using temperature programmed desorption (TPD) experiments, both in the presence and in the absence of SO2. In general in the presence of both H2O and SO2 the catalyst does not show any sign of deactivation at temperatures above 300°C and fairly low space velocities (below 12,200h−1). However, at lower temperatures (250°C) and/or higher space velocities the catalytic performance for NOx reduction decreases with time.

Catalytic Pyrolysis of Pine Biomass Over H-Beta Zeolite in a Dual-Fluidized Bed Reactor: Effect of Space Velocity on the Yield and Composition of Pyrolysis Products

A dual-fluidized bed reactor was applied in the pyrolysis of pine wood and catalytic upgrading of the pyrolysis vapors over H-Beta zeolite. The temperatures of the pyrolysis and catalytic upgrading reactors were 400 and 440 °C, respectively. The effect of space velocity on the yield and composition of pyrolysis products was investigated. It was found that the catalytic upgrading affects all pyrolysis products, except the char yield which can be considered constant at all space velocities. By lowering the space velocity the gas, water and coke yields increased at the cost of the organic phase of the bio-oil. The coke yield was fairly high, 11 wt% of the biomass, at the lowest space velocity. The spent catalysts could be regenerated by burning away the formed coke and thereby regaining the surface area and most of the acid sites.

Product distributions of Fischer-Tropsch synthesis over Co/AC catalyst

The product distributions of Fischer-Tropsch synthesis over Co/AC catalyst are investigated under different reaction conditions in an integral fixed bed reactor. It is found that the product distributions deviate from the ASF distribution. The deviation from ASF distribution is analyzed by taking the readsorption of alkenes and the following secondary reaction into consideration. It is noted that the contents of alcohol, alkene and alkane decline with the increasing carbon number, showing a slighter declining tendency of alkanes than those of alkenes and alcohols. It is also found that high temperature, space velocity, H 2/CO in feed gas and low pressure are preferential for light hydrocarbons and alcohols while against the chain propagation. The effect of space velocity on the product distributions especially on the light products is not obvious. It is noticed that low temperature, space velocity, H 2/CO and high pressure lead to high contents of alcohols; high temperature, H 2/CO and low space velocity lead to high contents of alkanes. The effect of pressure on the amounts of alkanes is not significant; high space velocity and low temperature, pressure, H 2/CO are preferential for alkenes.

Steam reforming of ethanol/gasoline mixtures: Deactivation, regeneration and stable performance

The steam reforming of 85% pure ethanol, 15% gasoline (E85) with and without sulfur was studied over a bimetallic precious metal (Rh/Pt) catalyst deposited on a ceramic monolith. Tests performed at low space velocities (22,000h−1) confirmed that the catalyst could achieve 100% ethanol and gasoline conversion to equilibrium concentrations of H2, CO, CO2 and CH4 with no signs of deactivation for at least 110h reforming a sulfur-free E85 fuel. In the presence of 5ppm sulfur the catalyst maintained 100% ethanol and 100% gasoline conversion for approximately 22h before rapid deactivation resulted in ethanol conversion values below 21%. TPO analysis established large carbon deposits had formed on the catalyst surface demonstrating that sulfur promoted carbon formation. Following such extensive deactivation full activity was recovered after treating the catalyst with air; however subsequent deactivation occurred more rapidly indicating that some amount of permanent damage had occurred. A process with preemptive regeneration via air treatment was studied and it was found to extend the period of stable activity.

Effects of operating parameters on oxidative coupling of methane over Na-W-Mn/SiO 2 catalyst at elevated pressures

Abstract The effects of operating parameters on oxidative coupling of methane (OCM) over Na-W-Mn/SiO 2 catalyst have been studied at elevated pressures of 0.2, 0.3 and 0.4 MPa under low gaseous hourly space velocity (GHSV) and low temperature conditions. Experimental results show that when the operating pressure is increased, C 2+ yield slightly decreases, while the maximum ratio of ethylene to ethane remains unchanged. Moreover, it has been found empirically that increase of pressure does not affect the catalyst behavior permanently, the catalyst recovers its original low pressure performance without hysteresis behavior by reducing the pressure. Under the investigated conditions, when oxygen is completely consumed, the increase of GHSV leads to improvement in C 2 selectivity, while C 3+ and CO x selectivities decrease slightly. The C 2+ selectivity increases by increase of nitrogen diluent in the feed, but the C 3+ hydrocarbons selectivities decrease with increase of nitrogen since it is possible that further dilution at high pressure may reduce the probability of collision between CH 3 and C 2+ hydrocarbons. During the stability test at high pressure, the catalyst performance remains unchanged throughout the 20 h running. The fresh and used catalysts were characterized using XRD, SEM and N 2 adsorption-desorption methods. It was found that the phase transformation of the support from α-cristobalite to tridymite and quartz does not have obvious effect on catalyst performance at high pressure.

Performance test of a bench-scale multi-tubular membrane reformer

Apart from H 2 production, hydrogen membrane reforming is also an attractive process for CO 2 capture when integrated in a natural gas fired power plant. In this study, a bench-scale multi-tubular Pd membrane reactor which has a capacity of 8.5 Nm 3/h H 2 product, was used to carry out the methane steam reforming reaction at near-practical working conditions: 823 K and up to 35 bar(a). The maximum CH 4 conversion and H 2 production rate were respectively achieved as 73.4% and 1.3 Nm 3/h at a feed/permeate pressure of 35/5 bar(a). A typical pre-reformed mixture (PR) was used as feed gas in this work, and was found to be more efficient than CH 4/H 2O mixture that is normally adopted in the literature. The steam sweep exhibited a similar effect as N 2 sweep except at very low space velocity that revealed steam outperforming N 2. Stable performance was found both for the membranes and the membrane reactor under the challenging conditions for over 30 days, showing a great potential of hydrogen membrane reforming for H 2 production. However, membrane reforming is found to be less attractive for CO 2 capture due to the low CH 4 conversion and consequent low driving force for transmembrane hydrogen transport at the high permeate pressure typical for NGCC operation.

Reactor modeling of sorption-enhanced autothermal reforming of methane. Part II: Effect of operational parameters

The process of sorption-enhanced autothermal reforming of methane is mathematically analyzed in a fixed bed reformer for pure H 2 production with in situ CO 2 capture at low temperature. A conventional Ni/MgO steam reforming catalyst is used. K-promoted hydrotalcite and lithium zirconate materials are examined as potential sorbents. A 1D heterogeneous dynamic fixed bed reactor model is constructed and employed in the study. The model accounts for mass and thermal dispersion in the axial direction, pressure drop, and intraparticle and interfacial resistances. The process performance is analyzed under dynamic conditions with respect to key operational parameters: gas hourly space velocity, oxygen/carbon ratio, steam/carbon ratio, catalyst/sorbent ratio, operating pressure, and particle size. The influence of these parameters on gas temperature, CH 4 conversion, H 2 yield and purity, and thermal reforming efficiency is demonstrated. The process is found to be benefited from low space velocity operation (0.05 kg/m 2 s), low pressure (4.47 bar), small particle size (0.5–1.0 mm), and high steam/carbon ratio (6). The high heat of reaction generated during the CO 2 chemisorption on lithium zirconate is also investigated if it is sufficient to provide a heat supplement at lower oxygen/carbon ratio at the adiabatic conditions of the autothermal reforming process. Oxygen/carbon ratio of less than 0.35 results in methane conversion of less than 95%.

Formation of hydrogen and filamentous carbon over a Ni–Cu–Al 2O 3 catalyst through ethane decomposition

The non-oxidative decomposition of ethane to yield hydrogen and nanostructured carbon was carried out over a Ni–Cu–Al 2O 3 catalyst in a quartz fixed bed reactor. The effects of temperature, which ranged between 550 and 750 °C, on the gas product distribution, ethane conversion, hydrogen selectivity and carbon yield were investigated. Additionally, the effect of the space velocity on the catalytic decomposition of ethane over the Ni–Cu–Al 2O 3 was studied. At low temperatures and low space velocities, H 2 and CH 4 were the only gas products detected, although low ethane conversions were obtained. As the temperature was increased, both the ethane conversion and hydrogen selectivity increased, along with the production of ethylene as a by-product. High space velocities lead to low ethane conversions and hydrogen selectivities, although the carbon yield was significantly enhanced. A plausible mechanism of product formation under the operational conditions studied is presented. Characterization of the catalysts following reaction was performed with N 2 adsorption, XRD, SEM and TEM; the results suggested that carbon was mostly deposited as fishbone-like nanofibers that differed, based on the operational conditions, on the catalyst growth mode (bi-directional growth at low temperatures vs. mono-directional growth at higher temperatures) and on the structural degree of order (higher at high temperatures and low space velocities).

10.2478/s11814-009-0317-1

Two mesoporous material Ni/γ-Al2O3 catalysts were prepared and characterized by ICP-AES, XRD, and TPR. The differences in reaction activity between Ni-in-Al2O3 and Ni-on-Al2O3 were investigated for hydrotreating of crude 2-ethylhexanol. The results show that the Ni species (Ni-on-Al2O3) exhibit excellent hydrogenation activities at a wide range of H2 pressure and space velocity, while the Ni species (Ni-in-Al2O3) exhibit similar activities with those of Ni-on-Al2O3 only at higher H2 pressure and lower space velocity. Due to the presence of extensively exposed Ni species on the Ni-on-Al2O3 catalyst, its hydrogenation performance was increased significantly because of the low interphase mass transfer resistance.

Methanol steam reforming over Cu/CeO2 catalysts: influence of zinc addition

Methanol steam reforming reaction was studied over Cu(5 wt.%)/CeO2 with and without the presence of Zn. The Zn addition decreased the Cu+2 reducibility and increased the oxygen mobility of ceria. The main products were CO2 and H2 with small amount of CO. Selectivity to CO decreased with the Zn addition and it was lower at lower reaction temperatures and lower space velocities. At 230 oC and W/FMeOH = 648 g min mol-1 selectivities to H2 and to CO2 were 100% on Zn/Cu/Ce. The catalytic results indicated that CO was mainly a secondary product formed from reverse water gas shift reaction.

Isobutane dehydrogenation in a DD3R zeolite membrane reactor

Dehydrogenation of isobutane has been studied in a DD3R zeolite membrane reactor (MR) at 712 and 762 K, using pure isobutane at 101 kPa as feed gas and N 2 as sweep gas. Clear advantage of using the small-pore zeolite DD3R is that it offers an absolute separation of H 2 from isobutane by a molecular sieving mechanism. Experiments in a conventional packed bed reactor served as benchmark. Cr 2O 3 on Al 2O 3 was used as catalyst. The DD3R membrane showed an excellent H 2/isobutane permselectivity (>500 @ 773 K) and a reasonable H 2 permeance (∼4.5 × 10 −8 mol m −2 s −1 Pa). At low residence times isobutene yields 50% above the equilibrium could be obtained. At 762 K and 0.13 kg feed kg cat −1 h −1, the isobutene yield in the membrane reactor (MR) is 0.41, where the equilibrium yield is ∼0.28. The increased performance is attributed to removal of H 2 from the reaction zone by the membrane, up to 85% at the lowest space velocity. The removal of H 2 mildly promotes coke formation, suppresses hydrogenolysis reactions and appears to slightly reduce the catalyst activity. The membrane permeation parameters and reaction rate constants have been estimated independently from membrane permeation and packed bed reactor (PBR) experiments, respectively. From these parameters the behaviour of the MR can be simulated well. Two important dimensionless parameters determine the MR performance primarily, the Damköhler ( Da) and membrane Péclet number ( Pe δ ). For a significant improvement of the MR performance as compared to a PBR Da ≥ 10 and Pe δ ≤ 0.1. DaPe δ should be ≈1 to optimally utilize both catalyst and membrane. In the current MR unit both the hydrogen removal capacity and catalyst activity stand in the way of successful application. Using a more active catalyst and a more favourable area to volume ratio could greatly improve the MR performance. Operation at a higher feed pressure could be a possible solution. Since membranes with higher fluxes are already available, the limited catalyst activity and stability under relative low temperature and H 2 lean conditions are the important limiting factors regarding application of MRs in dehydrogenation reactions.

Ni catalysts supported on modified ZnAl 2O 4 for ethanol steam reforming

Nickel catalysts supported over ZnAl 2O 4 modified by Ce or/and Zr addition were studied in the steam reforming of ethanol under more severe reaction conditions such as a lower extent of feed dilution and lower space velocities. The catalysts were stable at 650 °C during 35 h in time on stream. The main reaction products were H 2, CO 2, CO, C 2H 4O and small amounts of CH 4 and C 2H 4. The catalyst supported over CeO 2–ZnAl 2O 4 was the most active and showed the highest hydrogen selectivity. The addition of ZrO 2 decreased the activity and favored the CO production. The lowest degree of Ni 2+ reduction over Ni/ZAZr could explain the worst performance of this system. Otherwise, the highest Ni 2+ dispersion and the high oxygen mobility from ceria or from Ni–Ce boundary allowed a higher residual activity and an improved coking resistance.

Reaction of primary and secondary products in a membrane reactor: Studies of ethanol steam reforming with a silica–alumina composite membrane

The steam reforming of ethanol over Na–Co/ZnO catalysts was investigated in a conventional packed-bed reactor (PBR) and in a membrane reactor (MR) fitted with silica–alumina composite membranes. Promotion with a moderate amount of Na (0.2–1.0 wt%) produced catalysts with stable ethanol conversion and product selectivity. At 523 K, the main products were H 2 (51%) and CH 3CHO (42%) with minor amounts of CH 4 (0.7%) while above 573 K the main products were H 2 (70%) and CO 2 (15%) with a small amount of CH 4 (2.4%). Higher cobalt loading, higher W:E ratio, higher reaction temperature and lower space velocity enhanced the conversion of ethanol to H 2 and CO 2 while reducing the formation of undesirable acetaldehyde. Contact time studies indicated that acetaldehyde was a primary product of ethanol reforming, while CO 2 and CH 4 were secondary products. The composite membranes were prepared by a chemical vapor deposition (CVD) method and had moderate H 2 permeances ((5.2–6.8) × 10 −8 mol m −2 s −1 Pa −1 at 623 K). The MR produced positive yield enhancements of the secondary products, including hydrogen, but yield reductions for the primary product, acetaldehyde, and this is explained from the effect of the membrane separation on the reaction network. Two membranes with similar permeances but different H 2 selectivity ratios (H 2/CH 4 = 60 and 350) were compared and it was found that the membrane with a higher H 2/CH 4 selectivity ratio gave a higher yield enhancement. A survey of membrane reactor studies indicated that the conversion enhancement in reforming reactions could be described by a parameter denoted the operability level coefficient (OLC) which is related to 1/DaPe.

The difference in hydrogenation performance between Ni-in-Al2O3 and Ni-on-Al2O3 for hydrotreating of crude 2-ethylhexanol

Two mesoporous material Ni/γ-Al2O3 catalysts were prepared and characterized by ICP-AES, XRD, and TPR. The differences in reaction activity between Ni-in-Al2O3 and Ni-on-Al2O3 were investigated for hydrotreating of crude 2-ethylhexanol. The results show that the Ni species (Ni-on-Al2O3) exhibit excellent hydrogenation activities at a wide range of H2 pressure and space velocity, while the Ni species (Ni-in-Al2O3) exhibit similar activities with those of Ni-on-Al2O3 only at higher H2 pressure and lower space velocity. Due to the presence of extensively exposed Ni species on the Ni-on-Al2O3 catalyst, its hydrogenation performance was increased significantly because of the low interphase mass transfer resistance.

Methane emission abatement by Pd-ion-exchanged zeolite 13X with ozone

The performance of 3 wt% Pd-ion-exchanged zeolite 13X for methane emission abatement under various parameters including reaction temperature (295–435 °C), inlet ozone concentration (0–4 vol%), space velocity (12 500–62 400 h−1) and inlet methane concentration (200 and 1400 ppm) were investigated. Without zeolite, gas phase reaction among methane, air and ozone gave 1–11% of methane conversion at 295–435 °C. The presence of inlet ozone (1.1–4 vol%) to the zeolite 13X system enhanced methane removal efficiency by 24–56%, giving an overall performance of 93% in this low temperature range. There existed a range of reaction temperatures where methane conversion was most enhanced by ozone in the zeolite system. Without ozone, methane oxidation showed an activation energy of 136 kJ mol−1. This was reduced to 116 kJ mol−1 by using 4 vol% of ozone. The enhanced methane removal efficiency was attributed to the decomposition of ozone to form atomic oxygen reacting with adsorbed methane. Higher percentage methane conversion was observed at lower space velocities under various inlet ozone concentrations. As the inlet ozone and methane concentration increased, the methane removal efficiency was limited by the number of available active sites in the zeolite, which governs the amount of adsorbed methane and atomic oxygen available for subsequent reactions. The system can be used for energy efficient green house gas and industrial effluent treatment.

Atmospheric hydrodesulfurization of diesel fuel using Pt/Al 2O 3 catalysts prepared by supercritical deposition for fuel cell applications

Hydrodesulfurization (HDS) of low-sulfur model and commercial diesel fuel (500 ppmw S) using Pt/Al 2O 3 catalysts prepared by supercritical carbon dioxide (scCO 2) deposition method is investigated at atmospheric pressure and in temperature range of 290–350 °C. The reactivity of the investigated organosulfur compounds followed the known trend, that is: BT > 2-MDBT > DBT ≫ 4-MDBT > 4,6-DMDBT, despite the nonconventional operating conditions and catalyst. The HDS of dibenzothiophenes was found to proceed only via the direct desulfurization route (C S bond scission) under the studied conditions whereas HDS at high H 2 pressure proceeds via both direct desulfurization and hydrogenation routes. This limitation had several consequences. Under atmospheric pressure, the HDS reaction exhibited low reactivity particularly towards the stericly hindered substituted dibenzothiophenes. HDS of commercial diesel at atmospheric pressure using catalyst prepared by supercritical fluid deposition technique was found to be feasible, however, the catalyst had to have high metal loading and the reactor had to be operated under high H 2/fuel ratio with low hourly space velocity.