High GHSV Research Articles

Catalytic syngas purification from model biomass gasification streams

Efficient cleaning and conditioning of biomass derived syngas for use in fuel synthesis continues to be a significant technical barrier to commercialising biofuels. The relative effectiveness of a range of nickel and rhodium containing catalysts for the conversion of model tar compounds (toluene and naphthalene or benzene) in a simulated bio-syngas stream containing up to 100ppm H2S and up to 5vol.% CH4 at temperatures from 700 to 900°C were assessed at JMTC.Though H2S was found to significantly reduce hydrocarbon conversion near complete conversion of methane and tar could be achieved on a Rh based catalyst at 900°C with a very high GHSV of 150,000h−1. At more realistic GHSV of 60,000h−1 and higher methane levels (5vol.%) the effect of H2S concentration on catalyst activity followed an apparent linear activity decay law. Furthermore, the H2S deactivation was fully reversible and could be attributed to a transient site-blocking mechanism (TSB).Selected catalysts were also evaluated at NREL for tar and methane conversions using oak modelled syngas. The best Ni and best Rh catalyst were then tested under real conditions using oak derived syngas from NREL's pilot scale gasification unit.Rh based catalysts gave significantly better hydrocarbon conversion than the Ni catalysts at comparable conditions. The best Rh catalyst demonstrated 200h of steady state methane conversion of 95% with little apparent loss of activity using oak modelled syngas.

Three-dimensional ordered mesoporous Co–Mn oxide: A highly active catalyst for “storage–oxidation” cycling for the removal of formaldehyde

Abstract Three-dimensional (3D) ordered cubic mesoporous Co–Mn oxide (denoted as CoMn-HT) was fabricated using a KIT-6-templating strategy and was tested in a “storage–oxidation” cycling process for the removal of formaldehyde. The formation of a 3D ordered mesoporous structure was confirmed by low-angle XRD, nitrogen adsorption–desorption data, and TEM micrographs. The CoMn-HT catalyst showed promising properties in both the storage and regeneration phases, and remained active in highly humid air (RH = 90%) and at high GHSV (160,000 h − 1 ). The excellent catalytic performance of CoMn-HT was associated with its large surface area and 3D ordered mesoporous structure.

Effects of reaction temperature on the photocatalytic activity of photo-SCR of NO with NH3 over a TiO2 photocatalyst

Effects of reaction temperature on the activity of photo-assisted selective catalytic reduction (photo-SCR) of NO with NH3 were investigated under very high GHSV conditions (100 000 h−1). The reaction temperature had a significant effect on the photo-SCR activity over a TiO2 photocatalyst. Maximum NO conversion was achieved at 433 K (NO conversion = 84%, N2 selectivity = 100%). The apparent activation energies in the low and high temperature range were evaluated to be 9.0 kJ mol−1 (353–433 K) and −2.7 kJ mol−1 (493–593 K), respectively. Kinetic analysis revealed that the rate-determining step in the photo-SCR was decomposition of NH2NO intermediates in all the ranges of the reaction temperature (353–593 K). The reaction temperature affects not only the rate constant of decomposition of NH2NO intermediates but also the total number of active sites ([S]0) and the equilibrium constant of NH3 adsorption, resulting in the dynamic change in the reaction rate.

Catalytic removal of formaldehyde at room temperature over supported gold catalysts

Two kinds of Au/CeO2, prepared by deposition–precipitation (DP) using urea (U) or NaOH (N) as precipitants were investigated as catalysts for HCHO oxidation. H2-TPR and XPS techniques were used to characterize the Au/CeO2 samples. Due to the generation of increased amounts of active surface oxygen species resulting from the strong Au–CeO2 interaction, the Au/CeO2 (DPU) catalyst showed higher activity than the DPN catalyst, achieving 100% conversion of HCHO into CO2 and H2O at room temperature, even in the presence of water and at high GHSV (143,000h−1); moreover, the conversion was stable for at least 60h. The reaction mechanism and the rate limiting steps for HCHO oxidation over the Au/CeO2 catalysts were identified by means of in situ DRIFTS studies. The influence of oxygen and water on the formation and consumption of the formate reaction intermediates was also investigated. Results suggest that Au/CeO2 (DPU) is a promising catalyst for HCHO removal under real world conditions.

Synthesis gas production to desired hydrogen to carbon monoxide ratios by tri-reforming of methane using Ni–MgO–(Ce,Zr)O2 catalysts

This paper highlights the performance of Ni–MgO–(Ce,Zr)O2 tri-reforming catalysts under various reaction conditions and explains results using catalyst characterization. Testing under controlled reaction conditions and the use of several catalyst characterization techniques (BET, XRD, TPR, SEM-EDS, and XPS) were employed to better explain the effects of the synthesis parameters on the reaction performances. The support Ce:Zr ratio, metal loading techniques, metal wt%, and Ni:Mg ratios all had a pronounced influence on the catalyst performance. An even ratio of Ce:Zr for the support and an even ratio of Ni:Mg gave the best performance. The wet impregnation method consistently showed more resistance to coke formation when compared to the deposition precipitation method, but the difference was attributed to a better ability to load Mg by wet impregnation. Lower than previously reported H2O concentrations in the feed gas composition also led to desired H2:CO ratios needed for FT synthesis while maintaining high conversions of CO2 and resistance to coke formation. High GHSV (61,000h−1) yielded significantly higher H2:CO ratios when compared to reactions run at lower GHSV (25,000h−1). These results suggest that steam reforming reactions are kept further from equilibrium at higher GHSV and result in higher H2 production. The tested tri-reforming catalyst produced desired H2:CO ratios with minimal deactivation, high reactant conversions, and extended catalyst lifetime.

Total methanation of syngas to synthetic natural gas over Ni catalyst in a micro-channel reactor

Methanation reaction from syngas to synthetic natural gas (SNG) has been successfully implemented over Ni catalyst in a micro-channel reactor with high conversion and selectivity in milliseconds contact time. A new method called improved thermal spray to manufacture the metal-ceramics complex substrate as catalyst support was presented. The substrate demonstrated dual functions, i.e., the superior heat conduction as metal and stable catalyst coating on it as ceramics (e.g., Al2O3). The experiments verified that the fall-off proportion of the catalyst can be neglected after the plates experienced methanation reaction and strong vibration in ultrasonic cleaner. Meanwhile, the catalyst coatings on the walls of micro-channel reactor showed high activity and stability, having the excellent catalytic performance for methanation reaction in micro-channel reactors and the reliability in long-term use as well. At the temperature of 550°C and the pressure of 30atm, CO conversion and CH4 selectivity can remain above 98% and 92%, respectively, at a high GHSV of 71,000h−1, where the corresponding residence time is only about 50ms. Extensive characterizations of these Ni catalyst plates were also made to get a better understanding of the catalytic performance. The results of XRD, SEM, TEM and TPR characterizations demonstrated that Ni catalysts prepared in this work did not show any sign of deactivation after being used in the micro-channel system. It is expected that the methanation reactor technique based on the metal-ceramics complex substrate as the catalyst support in (micro-)channel reactors would open opportunities for the reliable engineering applications of either distributed or mass production of SNG from syngas.

HC-SCR on Silver-Based Catalyst: From Synthetic Gas Bench to Real Use

ABSTRACT The challenge for decreasing the emissions of compression ignition engines now remains mainly on NOx control. If the Lean NOx Trap (LNT) and Selective Catalytic Reduction by Urea (Urea-SCR) are very efficient, their extra-cost and management are a major issue for the OEMs. In that context, the selective catalytic reduction by hydrocarbons (HC-SCR) appears to be an interesting alternative solution, with a more limited NOx conversion efficiency but an easier packaging (diesel fuel as a reductant) and a limited price (reasonable coating cost / no PGM). In the framework of the RedNOx project, a prototype catalyst made of 2% silver on Alumina coated on cordierite was manufactured and tested on a synthetic gas bench. In parallel, an exhaust implementation study has been led to ensure the most suited conditions for injection. Thanks to SGB and simulation results, adapted engine tests have been designed and performed. If the results on SGB are consistent with the literature with a maximum NOx conversion reaching about 70% and an operating range between 300 and 500°C, first engine results were very disappointing showing efficiencies lower than 15% for all the operating points. Three guidelines for improving these results were identified and studied: • The way the reductant is introduced in the exhaust, especially the discontinued HC delivery due to the injection pattern • The gas velocity: unusual small GHSV values for automotive applications are needed to ensure a good NOx conversion rate. • The nature of the used reductant. Diesel fuel (ULSD) compared with decane lowers the efficiency, but synthetic Diesel fuel (SD) and, moreover, ethanol, largely improve it, especially for high GHSV.

Oriented linear cutting fiber sintered felt as an innovative catalyst support for methanol steam reforming

A kind of oriented linear cutting fiber sintered felt as an innovative catalyst support for methanol steam reforming was proposed. Multiple long copper fibers fabricated by cutting method were arranged in parallel and then sintered together in a mold pressing equipment under the condition of high temperature and protective gas atmosphere. The characteristics of oriented linear cutting fiber sintered felt coated with Cu/Zn/Al/Zr catalyst for methanol steam reforming were experimental investigated under different GHSVs and reaction temperatures. Results indicated that the structure of sintered felt was the key influencing factor for the reaction performances on the condition of low GHSV or reaction temperature whereas the structure of sintered felt showed little influences with high GHSV or reaction temperature. By the analysis of SEM image and ultrasonic vibration testing method, it was found that the coarse surface pattern of cutting fiber could effectively enhance the adhesion intensity between the catalyst and the copper fibers, as well as present relatively large specific surface area in the microchannels. And hence the oriented linear cutting fiber sintered felt present better performances of methanol steam reforming than the oriented linear copper wire sintered felt on the condition of low GHSV or reaction temperature.

Novel cerium–tungsten mixed oxide catalyst for the selective catalytic reduction of NOx with NH3

A novel Ce-W mixed oxide catalyst prepared by homogeneous precipitation method presented nearly 100% NO(x) conversion in a wide temperature range from 250 to 425 °C for the selective catalytic reduction of NO(x) with NH(3) under an extremely high GHSV of 500,000 h(-1).

Vapor phase oxidation of dimethyl sulfide with ozone over ion-exchanged zeolites

This work studied the catalyst activity and stability of ion-exchanged zeolites during the oxidation of dimethyl sulfide (DMS) in the presence of ozone. Ozone was used as an oxidant to assess the oxidation capability of Ag/ZSM-5, Mn/ZSM-5 and Ag-Mn/ZSM-5 of DMS at both room temperature and 130 °C. Ion-exchange with silver ions (Ag +) strengthened the adsorption of DMS, resulting in an increased oxidation capacity for DMS. Furthermore, the introduction of manganese ions (Mn 2+) strengthened the oxidation capability of DMS, thus enhancing the selectivity of SO 2 obtained from the oxidation and reducing the degradation of activity because the pores of the catalyst were blocked by the oxidation products, such as dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO 2). Ag-Mn/ZSM-5 demonstrated a 100% conversion of DMS; not only SO 2 but also H 2SO 3 and H 2SO 4 were detected at a high GHSV (90,000 h −1) and low reaction temperature (130 °C). The SO 2 adsorption curve and temperature-programmed desorption (TPD) showed that the single metal ion-exchanged zeolite had a weak adsorption capability for SO 2 at room temperature, whereas the bi-metal ion-exchanged zeolite had an excellent adsorption capability towards SO 2; it could convert SO 2 into H 2SO 3 and could convert oxidized SO 2 into H 2SO 4 in gas phase at room temperature.

Novel surface pretreatment for metal structured catalyst

The novel surface pretreatment is successfully developed to strengthen the adherence of catalyst via the oxidative formation of the uniform metal oxide layer on the metal substrate, which plays an important role as a binder between metal substrate and catalyst layer. The developed pretreatment method can be applied without regard to shape and composition of metal support. The surface pretreated metal structured catalysts are adopted to the natural gas steam reforming, showing a CH 4 conversion of 82% and stability for 120 h at high GHSV of 31,000 h −1, while conventional metal structured catalysts quickly deteriorates.

Low temperature NH3-SCR reaction over MnOx supported on protonated titanate

In the present work, protonated titanate nanoribbons were prepared by hydrothermal treating of TiO2 in alkali solution, followed by a thorough acid washing. The protonated titanate nanoribbons were employed as novel support for MnOx species and MnOx/protonated titanate was studied as a promising catalyst for the low temperature NH3-SCR reaction. The maximal NO conversion of ca. 98% was achieved over MnOx/protonated titanate at 200 °C under high GHSV of 50000 h−1. The existence of both MnO2 and Mn2O3 as active Mn species on protonated titanate was confirmed by XPS analysis, which was responsible for the high deNOx activity of MnOx/protonated titanate in NH3-SCR reaction.

Study on Pt/Al-MCM-41 for NO selective reduction by hydrogen

Al species can be introduced to the framework of Si-MCM-41 support by isomorphous substitution or wet impregnation and Brønsted acid sites can be created in Al-MCM-41. Pt catalysts supported on Si-MCM-41 and Al-MCM-41 are studied for the selective catalytic reduction of NO by hydrogen in excess oxygen. The introduction of Al species to MCM-41 at suitable Si/Al ratio shows great promotion effect on H 2-SCR over Pt/MCM-41. Pt catalyst supported on Al-MCM-41 prepared by isomorphous substitution with the Si/Al ratio of 10 exhibits the best catalytic performance and ca. 80% NO x conversion as well as ca. 85% N 2 selectivity can be achieved at 140 °C at high GHSV of 80,000 h −1. The H 2-SCR reaction over Pt/Al-MCM-41, together with Pt/Si-MCM-41, are investigated by means of in situ DRIFT spectra and the existence of Brønsted acid sites in Al-MCM-41 is found to play a decisive role on the H 2-SCR reaction pathway.

Low temperature H2-SCR over platinum catalysts supported on Ti-containing MCM-41

A series of Ti-containing MCM-41 were prepared by isomorphously substitution, wet impregnation and mechanical mixing. Ti-containing MCM-41 materials, together with reference Si–MCM-41, were characterized by means of XRD, TEM and low temperature N2 adsorption/desorption. The nature of Ti species on Ti-containing MCM-41 was analyzed by means of UV–vis and Raman spectroscopy. Pt catalysts supported on Si–MCM-41 and Ti-containing MCM-41 were studied for the selective catalytic reduction of NO by hydrogen in excess oxygen. Particular attention was paid to the promotion effect of different Ti species on the catalytic activity for H2-SCR and the origin thereof. Pt/Ti–MCM-41 prepared by wet impregnation with the Ti/Si ratio of 0.6 exhibited the best activity and ca. 89% NOx conversion as well as ca. 79% N2 selectivity, could be achieved at 140°C with a feed stream containing 1000ppm NO, 5000ppm H2, 6.7% O2 at a high GHSV of 80,000h−1. Moreover, Pt–Ti–MCM-41 exhibited good duration and good tolerance to co-existing 20ppm SO2 or 50ppm CO, which demonstrated its potential for future applications.

Combined XRD and XANES studies of a Re-promoted Co/γ-Al 2O 3 catalyst at Fischer–Tropsch synthesis conditions

A cobalt based Fischer–Tropsch catalyst was studied during the initial stages of the reaction at industrially relevant conditions. The catalyst consists of 20 wt% cobalt supported on γ-Al 2O 3 and promoted by 1 wt% of rhenium. X-ray diffraction (XRD) in combination with X-ray absorption near edge structure (XANES) were used to reveal information on the particle and crystallite size and the oxidation states of the active component. Conditions giving high selectivity towards light hydrocarbons (methanation, 673 K, 10 bar and high GHSV) were compared to conditions were higher hydrocarbons are the main products (FT synthesis at 483 K, 18 bar and low GHSV). The data analysis shows no significant changes in the cobalt crystallites during the first hours of Fischer–Tropsch synthesis. Running the reaction at higher temperatures and predominantly methanation conditions led to significant sintering of the cobalt particles and a further reduction of a partially reduced catalyst could be observed.

Small-sized HZSM-5 zeolite as highly active catalyst for gas phase dehydration of glycerol to acrolein

The catalytic properties of nanocrystalline HZSM-5 catalysts with high Si/Al molar ratio (ca. 65) were investigated in the gas phase dehydration of aqueous glycerol. Compared with bulk HZSM-5, the small-sized catalyst exhibits greatly enhanced catalytic performance in glycerol dehydration even with very high GHSV (=1438 h −1). Catalysts with different Si/Al ratios were studied, but it is difficult to separate the influence of Si/Al ratio from that of particle size. However, by varying the proton exchange degree for one mother batch of zeolite, a series of H x Na 1 –x ZSM-5 catalysts with same particle size and different Brønsted acid site densities was prepared. The catalytic results for this series of samples show that high density of Brønsted acid sites favors the production of acrolein. Based on these results, small-sized HZSM-5 with high aluminum content appears to be most promising for gas phase dehydration of glycerol.

Catalytic oxidation of NO over TiO2 supported platinum clusters I. Preparation, characterization and catalytic properties

The oxidation of NO to NO2 was studied on Pt/TiO2 catalysts prepared by wet impregnation and photo-deposition method. Pt/TiO2 prepared by photo-deposition exhibited quite higher activity for NO oxidation to NO2 than that prepared by wet impregnation and over 90% NO conversion could be achieved at below 250°C at a high GHSV of 180,000h−1. The effects of catalysts pretreatment conditions and feed gas composition, i.e. SO2 and H2O in the stream, on NO oxidation were investigated in details. The different Pt/TiO2 samples were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The Pt-TiO2 electron-interaction was studied based on the characterization results and the role of Pt-TiO2 electron-interaction on the catalytic performance of Pt/TiO2 was further discussed.

Structured catalytic substrates with radial configurations for the intensification of the WGS stage in H 2 production

Weight and size reduction of fuel processing reactors is one of the key issues in the development of catalytic H 2 production and purification systems for distributed power plants. The search for innovative solutions is focused on the development of both catalyst formulations and geometries which could help to achieve an effective process intensification. Precious metals based structured catalysts in form of monolith or foam prepared from ceramic or metallic substrates could be a viable option to overcome heat transfer limitations, which typically characterize these systems. They allow high efficiency of fuel conversion even at high GHSV, and better stability and durability, a critical issue for industrial WGS catalysts. In this work we report on the development of an integrated kW-scale system, CH 4 fuelled, for H 2 production arranged with an autothermal reforming (ATR) and a WGS stage. Both reactors operated with noble metals based structured catalysts. Since in an adiabatic WGS reactor the reaction rates are not optimized throughout the reactor we employ noble metals foam structured catalysts assembled in such a way to perform inside the reactor axial or radial gas flow geometry. The aim of the work is to verify the influence of flow geometry on the reformer performance.

Evaluation of reactor and catalyst performance in methane partial oxidation over modified nickel catalysts

The process of catalytic partial oxidation (CPO) of methane was investigated at moderate furnace temperatures (500–973 K) and 1 atm over a series of modified Ni catalysts. By exposing the catalysts to different GHSV (15–600 N l CH 4/g h), the conditions ranged from approaching equilibrium at bed exit gas temperatures to oxygen break-through with associated effects on methane conversion and product composition. By modifying Ni catalysts we illustrate that the expected availability of reducible oxygen species influence the combustion activity of the catalyst. This is reasoned from observations of stronger temperature gradients and a higher maximum gas temperature with modifiers such as Co, Mo, Pt, Pd, Rh and to some degree Cr, as compared to a pure Ni catalyst. Modifiers which are generally difficult to reduce, such as oxides of W, Fe and Mn did not increase combustion activity at the bed entrance. At conditions where oxygen break-through was observed, the formation of coupled products, in particular ethane was promoted. It is reasoned that hetero-homogeneous coupling may be involved. The pure Pt and Pt-modified Ni catalysts were found to promote ethane formation even at 100% oxygen conversion. Interestingly, we here report results suggesting a direct route to synthesis gas over Rh, most likely working in parallel to a combustion reforming mechanism at high GHSV. This is argued based on an evaluation of water-gas-shift and the H 2/CO ratio at low bed exit gas temperatures. The conclusion appears reasonable even when accounting for a potentially higher surface temperature than gas temperature.

Oxidation of nitric oxide to nitrogen dioxide over Ru catalysts

A series of TiO2 supported catalysts were prepared by impregnation method in a rotary evaporator and evaluated for the oxidation of NO to NO2. Among all catalysts studied, Ru/TiO2 catalyst exhibited the best activity and a maximal NO conversion of c.a. 94% could be achieved at c.a. 275°C at a high GHSV of 180,000h−1. For ruthenium catalysts, the effects of supports, ruthenium loadings, pretreatment conditions and experiment conditions (feed gas composition, GHSV) on NO oxidation to NO2 were investigated in detail. The ruthenium catalysts were characterized by means of X-ray diffraction (XRD), CO pulse chemisorption, transmission electron microscopy (TEM) and temperature-programmed reduction (TPR) techniques. The active ruthenium species for NO oxidation were discussed based on the catalytic and characterization results. Moreover, the reaction mechanism for NO oxidation over Ru/TiO2 catalyst was studied by means of in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS).