Catalyst Characterization Studies Research Articles

Dual Atom Catalysts for Energy and Environmental Applications.

The pursuit of high metal utilization in heterogeneous catalysis has triggered the burgeoning interest of various atomically dispersed catalysts. Our aim in this review is to assess key recent findings in the synthesis, characterization, structure-property relationship and computational studies of dual-atom catalysts (DACs), which cover the full spectrum of applications in thermocatalysis, electrocatalysis and photocatalysis. In particular, combination of qualitative and quantitative characterization with cooperation with DFT insights, synergies and superiorities of DACs compare to counterparts, high-throughput catalyst exploration and screening with machine-learning algorithms are highlighted. Undoubtably, it would be wise to expect more fascinating developments in the field of DACs as tunable catalysts.

Photo-degradation of sugar processing wastewater by copper doped bismuth oxyiodide: Assessment of treatment performance and kinetic studies.

In this study, photo-Fenton-like oxidation method was evaluated for synthetic sugar industry wastewater using visible-light driven Cu-BiOI photocatalyst. Reaction conditions including initial pH, catalyst loading, initial hydrogen peroxide (H2O2) concentration, and temperature, were optimized. At these optimized conditions, the total saccharide concentration (TSC) and total organic carbon (TOC) removals were 56.20% and 30.67%, respectively whereas the maximum TSC and TOC removal reached up to 93.35% and 74.72% respectively by decreasing initial sucrose concentration. The kinetic study showed that the reaction order for sucrose and TOC oxidation was determined as 2 for pseudo-homogeneous power law models with respect to sucrose concentration and TOC, respectively.For heterogeneous models, Langmuir-Hinshelwood model based on the mechanism of adsorbed pollutant and oxidant on different catalytic sites was the best fit for oxidation of sucrose and other organic intermediates. According to the catalyst characterization studies, incorporation of copper was successful and Cu-BiOI possesses high photocatalytic activity accomplished by acid-assisted synthesis method.

Sustainability in Biofuel Production Technology

It is highly desirable but quite challenging to replace precious metals with cheaper elements in the catalytic selective hydrogenation of unsaturated aldehydes. Herein, we report the preparation of a series of CuxNi3−xAlOy mixed-metal oxides (x = 0.5, 1, 2) derived from CuxNi3−xAl hydrotalcite to be used as catalysts for the promotion of the selective hydrogenation of furfural (FAL) to furfuryl alcohol (FOL). It was found that the catalyst with the Cu2Ni1AlOy stoichiometry exhibited the best performance, with 98% FAL conversion and 99% selectivity toward FOL after 1.5 h at 120 °C and under a H2 pressure of 1.6 MPa, and also good reusability. On the basis of the combined results from catalyst characterization studies using XRD, H2-TPR, TEM, XPS, and in-situ FT-IR, it was concluded that the CuOx species on the surface of the CuxNi3−xAlOy catalysts can be reduced in situ to metallic copper during reaction, and that this Cu0 species is likely the responsible for the adsorption and conversion of FAL. The addition of Ni to these mixed-metal oxides helps disperse the Cu phase and hence make it easier to reduce and activate. It may also be that NiO can promote H2 dissociation to aid with the hydrogenation catalysis. Our work advances a new strategy for the design of simple, cheap, and efficient catalysts for the hydrogenation of FAL to FOL.

Kinetic, Stability and Characterization Studies of Ce, Mn and Mn-doped Ceria Paper Catalysts Towards Soot Combustion Under Different Reaction Conditions

Kinetic, Stability and Characterization Studies of Ce, Mn and Mn-doped Ceria Paper Catalysts Towards Soot Combustion Under Different Reaction Conditions

Parametric optimization of calcined and Zn-doped waste egg-shell catalyzed biodiesel synthesis from Hevea brasiliensis oil

The utilization of waste sources for energy development is increasingly gaining popularity because of its two-fold benefit to the environment. The present study discusses the synthesis of biodiesel from commercially available rubber seed oil using two catalysts: CaO derived from calcined waste egg-shells and Zn-CaO prepared by doping ZnSO4 onto the calcined egg-shells through wet impregnation. An L9 Taguchi matrix was used to optimize the process, and can accomodate 4 parameters at 3 levels each. Data obtaind was used for a comparative evaluation of their catalytic performance. During catalyst characterization studies, morphological analyses showed the effectiveness of calcination in development of a porous structure that was capable of adsorbing Zn in high quantities, which was further verified through spectral analyses. Using CaO the optimal biodiesel yield noted was 80.2%, while Zn-CaO enabled a biodiesel yield of 94.12%. The optimal conditions were a reaction temperature of 55°C, methanol to oil molar ratio of 12:1, catalyst concentration of 5% w/w for both catalysts within a reaction duration of 1.5 h (for CaO) and 2 h (for Zn-CaO). Fuel characterization tests through ASTM prescribed procedures showed that the obtained product has acceptable physico-chemical properties and is thus suitable for use as biodiesel. Reusability studies (tested up to 4th reuse) indicated that CaO loses its catalytic efficiency much faster compared to Zn-CaO, primarily due to the vacant active sites in CaO being blocked by increased adsorption of organic molecules during the transesterification phase compared to Zn-CaO.

Investigation of isobutane dehydrogenation on CrOx/Al2O3 catalyst in a membrane reactor

Isobutene is an important raw material for the production of additives that increase the octane number of gasoline and reduce emissions, some polymeric materials and pharmaceuticals. Isobutane dehydrogenation, which is widely used in the production of isobutene, is an equilibrium-limited endothermic reaction. In this study, it was aimed to overcome the equilibrium conversions by using membrane reactor. First, Al2O3 supported chromium-based catalysts were prepared by the impregnation technique. Characterization studies of catalysts were carried out by DR..........-UV–vis, N2 adsorption/desorption, XRD and SEM/EDS analyses. Catalysts (6% Cr by mass) were prepared at three different values of the contact time - 24, 48, 72 h mixing times. The highest amount of monochromate was observed in the catalyst prepared during the mixing time of 48 h. Catalysts containing 6%, 8%, and 10% Cr by mass (mixing time: 48 h) were also synthesized. When the chromium concentration increased above 8%, a decrease in the amount of monochromate was observed. Then, reactions were performed with a catalyst containing 8% by mass of Cr, which was prepared in a mixing time of 48 h with the highest amount of monochromate. The reactions were carried out in a Pd based membrane reactor system with pure isobutane feed. The effect of reactor temperature was investigated at 550 °C and 600 °C (WHSV:0.3h−1). While no significant difference was observed between the conversion values at both reactor temperatures (⁓90%), isobutene selectivity values were higher (⁓85%) at 600 °C. It was observed that the high isobutene selectivity values determined at 600 °C were due to the high endothermic nature of the reaction. The reaction was also carried out by changing the weight hourly space velocity at 600 °C (WHSV:0.5h−1). Although the isobutane conversion values were close to each other (⁓90%), higher isobutene selectivity values (⁓90%) were determined at 0.3h−1. The presence of less hydrogen in the environment decreased the formation of the hydrogenation reaction of isobutane. This situation enhanced an increase in isobutene selectivity values. The shift of the reaction towards the products also increased the selectivity of isobutene. It was observed that although the amount of carbon (3 times more) formed at high retention times caused negative effects such as a decrease in the surface area and closure of the pores, the active monochromate species preserved in the catalyst structure. It was determined that the formed amorphous carbon did not cause the rapid decreases in activity and selectivity. The results of the study showed that the equilibrium limitation could be overcome by removing hydrogen from the reactor medium (equilibrium conversions:73% at 600 °C, 53% at 550 °C). The results of the modeling studies carried out in the membrane reactor were found to be compatible with the experimental results.

Catalytic co-conversion of glycerol and oleic acid to bio-aromatics: Catalyst deactivation studies for a technical H-ZSM-5/Al2O3 catalyst

The catalytic co-conversion of glycerol and oleic acid (45/55 wt%) to bio-based aromatics (benzene, toluene, and xylenes, bio-BTX) over a technical H-ZSM-5/Al2O3 catalyst in a fixed-bed reactor was investigated with special attention to catalyst deactivation phenomena. The spent catalysts after a time on stream (TOS) of 12 h were regenerated by an ex-situ oxidative treatment to remove coke and reused for another run. In total, 5 reaction-regeneration cycles were performed. The performance and characteristics of the fresh and regenerated catalysts were determined to identify and quantify the effects of co-feeding on catalyst stability and regenerability. The performance of the catalyst changes upon the number of reaction-regeneration cycles. Despite a negative effect on the peak BTX yield, a remarkable improvement in catalyst stability was found, leading to higher BTX productivity (1260–1505 gBTX gcat-1 for the regenerated catalysts during a TOS of 12 h vs. 834 gBTX gcat-1 for the fresh one during a life-time of 11 h). Detailed catalyst characterization studies show irreversible changes in the catalyst structure after reaction-regeneration cycle(s), such as textural property, crystal structure, framework, and acidity, which impact catalyst performance.

Catalytic hydrogenation of furfural to furfuryl alcohol on hydrotalcite-derived CuxNi3−xAlOy mixed-metal oxides

It is highly desirable but quite challenging to replace precious metals with cheaper elements in the catalytic selective hydrogenation of unsaturated aldehydes. Herein, we report the preparation of a series of CuxNi3−xAlOy mixed-metal oxides (x = 0.5, 1, 2) derived from CuxNi3−xAl hydrotalcite to be used as catalysts for the promotion of the selective hydrogenation of furfural (FAL) to furfuryl alcohol (FOL). It was found that the catalyst with the Cu2Ni1AlOy stoichiometry exhibited the best performance, with 98% FAL conversion and 99% selectivity toward FOL after 1.5 h at 120 °C and under a H2 pressure of 1.6 MPa, and also good reusability. On the basis of the combined results from catalyst characterization studies using XRD, H2-TPR, TEM, XPS, and in-situ FT-IR, it was concluded that the CuOx species on the surface of the CuxNi3−xAlOy catalysts can be reduced in situ to metallic copper during reaction, and that this Cu0 species is likely the responsible for the adsorption and conversion of FAL. The addition of Ni to these mixed-metal oxides helps disperse the Cu phase and hence make it easier to reduce and activate. It may also be that NiO can promote H2 dissociation to aid with the hydrogenation catalysis. Our work advances a new strategy for the design of simple, cheap, and efficient catalysts for the hydrogenation of FAL to FOL.

Improved catalyst formulations for the conversion of glycerol to bio-based aromatics

The catalytic conversion of glycerol to aromatics (GTA, e.g., benzene, toluene, and xylenes, BTX) over a shaped H-ZSM-5/Al2O3 (60/40 wt%) catalyst was investigated in a continuous fixed-bed reactor to study the addition of the Al2O3 binder in the catalyst formulation on catalyst performance. The experiments were performed under N2 at 550 °C, a WHSV of glycerol (pure) of 1 h−1, and atmospheric pressure. The spent H-ZSM-5/Al2O3 catalysts were reused after an oxidative regeneration at 680 °C and in total 5 reaction-regeneration cycles were performed. Catalyst characterization studies show that the addition of the Al2O3 binder does not affect the surface area and crystallinity of the formulation, but increases the total pore volume (mesopores in particular) and total acidity (Lewis acidity in particular). The H-ZSM-5/Al2O3 (60/40 wt%) catalyst shows a considerably prolonged catalyst life-time (8.5 vs. 6.5 h for H-ZSM-5), resulting in a significant increase in the total BTX productivity (710 vs. 556 mg g−1 H-ZSM-5). Besides, the addition of the Al2O3 binder retards irreversible deactivation. For instance, after 3 regenerations, catalyst performance is comparable to the fresh one. However, after 4 regenerations, some irreversible catalyst deactivation occurs, associated with a reduction in total pore volume, crystallinity, and acidity (Brønsted acidity in particular), and meso-porosity of the Al2O3 binder. This study shows that both the stability and reusability of H-ZSM-5-based catalysts for GTA are remarkably enhanced when using a suitable binder.

Bioethanol Upgrading to Renewable Monomers Using Hierarchical Zeolites: Catalyst Preparation, Characterization, and Catalytic Studies

Bioethanol is one of the most promising renewable resources for the production of important monomers. To date, there have been various processes proposed for bioethanol conversion to renewable monomers. In this review, the catalytic bioethanol upgrading to various types of monomers using hierarchical zeolites as catalysts is illustrated, including the recent design and preparation of hierarchical zeolites for these catalytic processes. The characterizations of catalysts including textural properties, pore architectures, acidic properties, and active species are also exemplified. Moreover, the catalytic studies with various processes of monomer production from bioethanol including bioethanol dehydration, bioethanol to hydrocarbons, and bioethanol to butadiene are revealed in terms of catalytic activities and mechanistic studies. In addition, the future perspectives of these catalytic circumstances are proposed in both economic and sustainable development contexts.

Catalytic conversion of glycerol to bio-based aromatics using H-ZSM-5 in combination with various binders

The use of H-ZSM-5 with various binders (Al2O3, SiO2, and kaolinite, 10 wt% on catalyst formulation) for the catalytic conversion of glycerol to bio-based aromatics (GTA) was investigated in a continuous bench-scale unit at a pyrolysis temperature of 450 °C, catalytic upgrading temperature of 500 °C, WHSV of pure glycerol of 1 h−1, and atmospheric pressure, and their performance was compared to H-ZSM-5 (SiO2/Al2O3 molar ratio of 28). The latter gave a peak BTX carbon yield of ca. 31.1C.%, a life-time of ca. 220 min, and a total BTX productivity of ca. 312 mg BTX g−1H-ZSM-5. The introduction of binders affects catalyst performance, which is the most profound and promising for the H-ZSM-5/Al2O3 catalyst. It shows a prolonged catalyst life-time of ca. 320 min and a higher total BTX productivity of ca. 518 mg BTX g−1H-ZSM-5, compared to the H-ZSM-5 without a binder. Catalyst characterization studies show that the addition of the binder does not have a major effect on the specific surface area, total pore volume, and total acidity. Other relevant properties were affected, though, such as micropore volume (SiO2), a reduced Brønsted acidity (Al2O3, and SiO2), and reduced crystallinity (SiO2). Coke formation causes severe catalyst deactivation, ultimately leading to an inactive catalyst for BTX formation. Catalyst characterization studies after an oxidative regeneration showed that the textural properties of the regenerated catalysts were close to those of the original catalysts. However, some dealumination of H-ZSM-5 occurs, resulting in decreased crystallinity and acidity, causing irreversible deactivation, which needs attention in future catalyst development studies.

Effective Heterogeneous MoOx‐Modified CeO2 Catalyst for Michael Addition of Dimethyl Malonate to 2‐Cyclohexen‐1‐one

AbstractMolybdenum oxide‐modified cerium oxide (MoOx−CeO2) with 1 wt % Mo acted as an effective and reusable heterogeneous catalyst for Michael addition of dimethyl malonate to 2‐cyclohexen‐1‐one, providing high yield of the target product (99 %). The catalyst showed higher activity with high selectivity (>99 %) than simple metal oxides and the other combination of metal oxides and CeO2. Based on the catalyst characterization and experimental studies, MoOx species in the MoOx−CeO2 catalyst are isolated Mo6+, and the interface between the isolated MoOx and CeO2 is the active site. The activity based on the active site was about 74‐fold and 1800‐fold higher than that of CeO2 surface and the typical strong organic base of DBU (1,8‐diazabicyclo[5.4.0]undec‐7‐ene), respectively.

CeO2@N/C@TiO2 Core‐shell Nanosphere Catalyst for the Aerobic Oxidation of 5‐Hydroxymethylfurfural to 5‐Hydroxymethyl‐2‐Furancarboxylic Acid

AbstractDefective D‐CeO2@N/C@TiO2 nanospheres, each comprising a spherical CeO2 core coated with shells of N‐doped carbon and TiO2, were successfully synthesized then evaluated for the aerobic oxidation of 5‐hydroxymethylfurfural (HMF) to 5‐hydroxymethyl‐2‐furancarboxylic acid (HMFCA). Detailed catalyst characterization studies using XRD, SEM, TEM, TG‐DTA, XPS, N2 physisorption confirmed the hierarchical core‐shell structure of the D‐CeO2@N/C@TiO2 nanospheres, with the defective surface structures created through a thermal hydrogenation process using NaBH4 promoting HMF conversion. The effect of various reaction parameters, including the reaction time, temperature, oxygen pressure, type of alkali co‐reactant and the amount of catalyst, on HMF oxidation to HMFCA over the D‐CeO2@N/C@TiO2 nanospheres were studied. Under the optimized reaction conditions (temperature 80 °C, reaction time 30 min, O2 pressure 1 MPa), a high HMF conversion of 87.8 % and a remarkable HMFCA selectivity of 100 % were obtained. In addition, the D‐CeO2@N/C@TiO2 nanosphere catalyst showed great stability over four consecutive HMF oxidation tests, implying good catalyst stability. Experimental findings were used to develop a plausible reaction mechanism for the selective oxidation of HMF on the D‐CeO2@N/C@TiO2 nanospheres.

Catalyst Performance Studies on the Guerbet Reaction in a Continuous Flow Reactor Using Mono- and Bi-Metallic Cu-Ni Porous Metal Oxides

Higher alcohols like 1-butanol are considered important biofuels with superior properties compared to the more readily available bio-ethanol. An attractive route to prepare 1-butanol from ethanol is the Guerbet reaction. We here report the use of hydrotalcite-derived mono- (Cu-PMO or Ni-PMO) and bi-metallic (CuNi-PMO) porous metal oxide catalysts for the Guerbet coupling of ethanol to 1-butanol in a continuous flow reactor (320 °C, 0.1 MPa, LHSV = 15 mL g−1 h−1) at extended times on stream (~160 h). Two distinct regimes with different product distributions were observed for the Cu-PMO and CuNi-PMO catalyst with time on stream. At the start of the run, the initial conversion of ethanol dropped from about 85% to less than 20% after 60 h and acetaldehyde was the main product (regime 1). At prolonged times on stream (60–160 h), fairly constant low conversions of ethanol (14%) were observed and 1-butanol was the main product (regime 2). Performance of the monometallic Cu-PMO catalyst in terms of 1-butanol yield and stability was lower compared to the bi-metallic CuNi-PMO. Detailed catalyst characterization studies (XRD, H2-TPR, sorption of acrylic acid, TGA, TEM, HAADF-STEM, and EDS mapping) on both fresh and spent CuNi-PMO taken at various times on stream was performed to determine the changes in catalyst morphology and composition during a run, and particularly to obtain information on changes in catalyst structure operating in regime 1 or 2. The change in chemoselectivity is in line with an increase in basicity of the catalyst at extended runtimes.

TiO2/anthill clay as a heterogeneous catalyst for solar photocatalytic degradation of textile wastewater: Catalyst characterization and optimization studies

This present study aims at revealing the activity of TiO2–anthill clay in photocatalytic degradation of textile effluent. It also aims to investigate the effects of parameters affecting the photocatalytic degradation process such as catalyst dose (0.5–25 wt.%), reaction time (1–3 h) and solution pH (2–10) through central composite design. The synthesized photocatalyst was characterized using BET, SEM, EDX, FTIR, and XRF techniques. The results obtained from the optimization studies revealed that there were good agreements between the predicted and observed values of photocatalytic degradation efficiency. The maximum decolorization efficiency of 70.92% was obtained under the optimum experimental conditions of 2.50 wt.% catalyst dose, 1.07 h reaction time, and dye solution pH of 2.0. The TiO2-anthill photocatalyst was found to be efficient for complete decolorization of dye solution as it was able to be reused for up to four cycles.

Deactivation mechanism of activated carbon supported copper oxide SCR catalysts in C2H4 reductant

Current state‐of‐the‐art NH3‐SCR technology based on vanadium catalysts suffers problems associated with NH3 slip and poisoning of the catalyst and blockage of heat recovery steam generators (HRSG). If environmentally‐friendly catalysts capable of efficient operation at lower temperatures could be developed that used a reductant other than NH3, the issues with current state‐of‐the‐art SCR could be significantly lessened. Hence, in this study, activated carbon (AC) supported copper oxide‐based catalysts for SCR while using C2H4 as a reductant was discussed. Reaction testing of catalysts demonstrated high initial NO conversion with steeply declining activity over 2 h of testing when C2H4 was used as the reductant; in comparison, with the same catalyst and NH3 as the reductant, stable, long‐term NO conversion was achieved, but at a lower rate than the initial reactivity with C2H4. As a consequence, catalyst characterization studies were performed to assess deactivation mechanisms when C2H4 was the reductant. These studies included x‐ray diffraction, BET surface area and porosity, temperature programmed reduction, scanning electron microscopy, Raman spectroscopy and x‐ray photoelectron spectroscopy of both fresh and deactivated catalysts. The analytical results showed the surface area and porosity of the catalyst remained unchanged and the initially highly‐dispersed Cu species became agglomerated and more crystalline during reaction testing. Furthermore, carbon black was also detected on the catalyst surface after testing, presumably formed during the decomposition of C2H4. Both agglomeration of the active Cu species and blockage by carbon deposits would decrease the availability of active sites and lead to decreased catalytic activity.

Effect of Co incorporation and support selection on deoxygenation selectivity and stability of (Co)Mo catalysts in anisole HDO

A series of supported Co modified Mo catalysts was prepared by varying the Co/Mo ratio in the range from 0 to 1 while maintaining the Mo loading at ca. 10 wt%. A sequential incipient wetness impregnation method, with Mo being introduced first, using aqueous solutions of the corresponding precursor salts was employed during the synthesis procedure. Three supports, i.e., Al2O3, ZrO2, and TiO2 differing in textural and acidic properties were investigated. Material physicochemical characteristics were evaluated through ICP-OES, N2-sorption, XRD, H2-TPR, NH3-TPD, O2-TPO, STEM-EDX and XPS techniques. The anisole HDO performance of these CoMo catalysts was evaluated at gas phase conditions in a fixed bed tubular reactor in plug flow regime. The catalysts performance is correlated with properties such as reducibility, acidity, and metal-support interactions. Cobalt addition enhanced the total HDO selectivity by 45% as compared to Mo catalysts. Alumina catalysts displayed higher initial activity (Xanisole≈97%) relative to titania and zirconia supported variants (Xanisole <40%) at identical operating conditions. Titania supported catalysts exhibited rather higher stability compared to zirconia and alumina catalysts over 50 h time on stream (TOS), while zirconia catalysts displayed the highest HDO selectivity (up to 86%). Characterization studies of pre and post-reaction catalysts indicate Mo5+ to be the main active phase while over-reduction to lower Mo states (Mo4+ and Mo3+) as well as carbon deposition are identified as the cause for catalyst activity decrease with TOS.

A proposed reaction mechanism for the selective oxidation of methane with nitrous oxide over Co-ZSM-5 catalyst forming synthesis gas (CO + H2)

Probable reaction intermediates and mechanistic steps involved for the selective oxidation of methane (CH4) with nitrous oxide (N2O) forming synthesis gas (CO + H2) over Co-ZSM-5 was examined. To assess the reaction kinetics reactions were conducted within a temperature range of 300 °C–550 °C and at atmospheric pressure, and the composition of reactant feed (N2O/CH4) was varied between three fixed ratios (5, 3, and 1). TPD, XRD, TEM and FT-IR techniques were used for catalyst characterization and mechanistic studies. It was found, that H2 selectivity is higher for feeds with lower N2O concentration. Furthermore, CO formation commences at lower temperatures in comparison to H2 gas which is a result of the formation of methanol (CH3OH) and carbon oxides (CO and CO2) at low CH4 conversions.Based on the reaction conditions, the literature proposes direct and an indirect mechanistic route for synthesis gas formation. Our catalytic study suggests a direct route for the synthesis gas formation; i.e. H2 gas is formed by the decomposition of intermediate species (methoxy and CH2O). This is supported by spectroscopic investigation. Under favourable reaction conditions and over the Co-ZSM-5 catalyst, N2O first oxidizes CH4 to CH3OH, an active reaction intermediate, which then subsequently is converted into (formaldehyde) CH2O and H2. CH2O is highly reactive and decomposes into CO and H2.

Surface characterization studies of walnut-shell biochar catalysts for simultaneously removing of organic sulfur from yellow phosphorus tail gas

The influences of different preparation conditions for surface characteristics on removing organic sulfur were studied. From BET, XRD, FTIR, DRIFTS, TG/DTA, CO2-TPD results, it can be seen that these preparation conditions had great influences on the pore structure, specific surface area, crystal structure and surface functional groups. The micropore volume, amorphous structure and alkalinity site strength played major roles in desulfurization process. H2S was oxidized by oxygen containing functional groups, such as COO, CO. H2O molecule could be converted into some groups, such as CH and COH groups, and promoted the hydrolysis reaction. The strong alkalinity site was the key factor for chemical adsorption and hydrolysis. H2O molecule, CH, COH groups promoted the hydrolysis reaction and COO, CO groups promoted the oxidation of H2S on the surface of WSB. Meanwhile, the main desulfurization process over WSB after carbonization was adsorption and it changed to hydrolysis reaction after activation on the surface of WSB. Furthermore, the reaction mechanism was investigated by DRIFTS measurement according to the change of surface functional groups.

Effect of Pt doping on activity and stability of Ni/MgAl2O4 catalyst for steam reforming of methane at ambient and high pressure condition

Effect of addition of Pt noble metal to Ni/MgAl2O4 catalyst for steam reforming of methane was studied at atmospheric pressure and at high pressure (10 bar). Pt loading of the catalyst was varied from 0.01 wt.% to 1.0 wt.%. Catalyst characterization studies showed that the degree of reduction of the catalyst increased from 44.9% for Ni/MgAl2O4 to 67.7% for the catalyst doped with 1.0 wt.% Pt, which was attributed to H2 spill over effect. With increasing Pt loading, the metal dispersion passed through a maxima and the highest dispersion of active metals was obtained with a Pt doping of 0.1 wt.%. Increase in Pt concentration had no effect on the concentration of NiAl2O4 that had already formed during calcination at 850 °C after nickel impregnation. Addition of Pt significantly increased the catalytic activity of Ni/MgAl2O4 for the steam reforming of methane at both reactor pressures. Comparison of Pt doped Ni/MgAl2O4 with Pt/MgAl2O4 showed that only lower loading of Pt produced a synergetic effect. The highest catalytic activity was obtained with 0.1 wt.% Pt doped Ni/MgAl2O4. Above this Pt loading the catalytic activity decreased. The highest activity of 0.1 wt.% Pt doped catalyst was credited to an increase in active metal dispersion, while the decrease in catalytic activity on further addition of Pt was attributed to agglomeration of active metals. High pressures decreased the conversion and stability of each Pt doped catalyst. However, at the same operating conditions there was a marginal increase in the catalyst stability due to Pt doping and the decline in catalyst activity with run time was lowest for 0.1 wt.% Pt doped Ni/MgAl2O4 catalyst.