Active Metal Surface Area Research Articles

Unveiling the potential of desert sand-derived mesoporous silica supported nickel-based catalysts for co-production of H2 and carbon nanomaterials via methane cracking

This study investigates the replacement of a costly commercial silicate source with locally abundant desert sand in the United Arab Emirates (UAE), for synthesizing mesoporous silica. Hydrothermal synthesis methods were employed to develop various mesoporous materials having different pore geometries, namely MCM41-S, SBA15-S and MCF-S, using desert sand as a silica source. These materials were then impregnated with 15 wt% NiO (∼13 wt% Ni) by sono-wet impregnation technique. All Ni-based silica supported catalyst demonstrated enhanced stability at 550 °C during the reaction. It was observed that the synthesized MCF-S proves to be a highly efficient catalyst support, as Ni/MCF-S, for the catalytic decomposition of methane (CDM), exhibiting the highest methane conversion (60 %), which is 1.4–2.1 times higher than the Ni-based classic-structured mesoporous siliceous supported catalysts, such as SBA15-S and MCM41-S. In particular, the H2 yield (62 %) of the Ni/MCF-S catalyst was 1.40 and 2.38 times higher than that of the Ni/SBA15-S and Ni/MCM41-S catalysts, respectively. To understand the observed differences, a detailed characterization of the physicochemical properties of these materials was conducted. The results revealed that the macro/mesopores size (4–60 nm) and bimodal sinusoidal pore geometry of MCF-S, played a critical role in enhancing Ni particle dispersion, resulting in the highest active Ni metal surface area (7.66 m2/gcat) and contributing to the improved catalytic activity of Ni catalysts in methane cracking.

Size-dependent selectivity and activity of highly dispersed sub-nanometer Pt clusters integrated with P25 for CO2 photoreduction into methane fuel

Integration of sub-nanometer–sized Pt cocatalysts on semiconductor materials is a promising approach to improve the activity and selectivity of CO2 photoreduction. However, the practical realization of such an integrated catalyst is a challenging task. We rationally integrated sub-nanometer Pt nanoclusters (Pt NCs) on the surface of commercial P25 catalyst by adjusting the amount of Pt loading. The lateral reduction in the size of Pt NCs resulted in high metal dispersion, increased active metal surface area, better CO2 adsorption, and hindered photoexcited charge-carrier recombination. The sub-nanometer Pt NCs integrated with P25 with a weight percentage of 0.5% (Pt-NC/P25-0.5) exhibited exceptional CO2 photoreduction activity for CH4 production and excellent stability during successive test runs. This catalyst outperformed its counterparts with larger Pt NCs and several previously reported state-of-the-art photocatalysts in terms of CH4 generation. Importantly, compared to its counterparts, Pt-NC/P25-0.5 had a higher proportion of edge and corner sites, which have a strong affinity for CO molecules, resulting in a high CH4 selectivity of 95% against H2. The size-dependent selectivity and activity of Pt NCs for CO2 reduction demonstrated in this study offer insights into the development of sub-nanometer metal-based catalysts for photocatalytic energy applications.

An Active K‐OMS‐2 Supported Catalyst for Hydrogenolysis of Glycerol

AbstractPropanediols are very important chemical intermediates, which need to be prepared through commercially viable routes. Cryptomelane type octahedral molecular sieve‐2 (K‐OMS‐2), a cheap and environmentally benign microporous oxide was employed to support Ru and used as a catalyst to get 1,2‐propanediol (1,2‐PDO) selectively through hydrogenolysis of glycerol. Three catalysts with different Ru content were prepared and evaluated for glycerol hydrogenolysis. Among these, 1 wt.% Ru‐K‐OMS‐2 showed reasonably good activity towards 1,2‐PDO formation under moderate reaction conditions even at lower Ru loading (0.9 wt.%). When other metals such as Cu and Ni were supported on K‐OMS‐2, their performance was inferior compared to Ru‐supported catalysts. All the catalysts were characterized using various physicochemical techniques like XRD, N2‐sorption, TPD, H2‐TPR, TGA, ICP‐OES, FE‐SEM and TEM. The enhanced catalytic activity with the 1 wt.%Ru‐K‐OMS‐2 catalyst was attributed to the better Ru metal dispersion, higher active metal surface area, basic strength, and porosity of the support. The catalyst was found to be recyclable. Analysis of spent catalyst by TEM showed disintegration of Ru nanoparticles to smaller ones, under high H2 pressure at the reaction temperature. Smaller Ru particles are expected to promote C−C bond cleavage thus suppressing 1,2‐PDO formation. Furthermore, a relationship between the TOF value, Ru nanoparticles size, and the basic strength of the catalysts was established, which provides dipper insight into the different catalytic behavior of the catalysts.

Gas phase transfer hydrogenation of α, β- unsaturated carbonyl compounds into saturated carbonyl compounds over supported Cu catalysts

This work aims to produce hydrocinnamaldehyde via selective CC bond hydrogenation of cinnamaldehyde via transfer hydrogenation catalyzed by supported Cu catalysts. The catalytic activity and characterization results demonstrated that conversion of cinnamaldehyde and selectivity to hydrocinnamaldehyde is an integrated result of active Cu metal surface area and nature of support material. In the case of Cu/SiO2 catalysts, the rate of formation of hydrocinnamaldehyde was linearly dependent on the active Cu metal surface area. A maximum rate of formation of hydrocinnamaldehyde 167.82 μmol.g−1.s-1 was obtained at an active Cu metal surface area of 6.1 m2.gcat-1 over 20 wt. % Cu/SiO2 catalyst. While in the case of other supported Cu catalysts (Cu/MgO, Cu/ZrO2 and Cu/γ-Al2O3) along with the active Cu metal surface area, the surface acidity and basicity governed the selectivity of hydrocinnamaldehyde. The rate of formation of hydrocinnamaldehyde followed the trend Cu/SiO2 >Cu/Al2O3 >Cu/MgO > Cu/ZrO2. Unlike Cu/SiO2 catalyst, the competitive adsorption of CC and CO bonds over these (Al2O3, MgO and ZrO2) supported Cu catalysts altered the selectivity of hydrocinnamaldehyde. Cu/SiO2 catalyst was superior in selective CC hydrogenation of α, β-unsaturated carbonyl compounds via transfer hydrogenation. Cyclohexenone, isophorone and crotonaldehyde were selectively converted into their saturated carbonyl compounds.

Pd-based Catalysts by Colloid Synthesis Using Different Reducing Reagents for Complete Oxidation of Methane

Here, without using any organic stabilizer, via two-steps process, Pd-based catalysts supported on La-modified Al2O3 by a new colloid synthesis method using different reducing reagents were prepared. It was found that the reducibility and structure of reducer controlled the rate of nucleation and growth of Pd in its precursor solution supported on the modified Al2O3. The surface OH groups of alumina can stabilize the formed Pd nanoparticles and enhance Pd dispersion. The catalyst obtained by using the mild reducing reagent, ethylene glycol, had the highest dispersion (32.6%) and largest active metal surface area. This catalyst showed the best catalytic performance among the five as-synthesized catalysts for removing pollutants in a simulated natural gas vehicles (NGVs) exhaust. Compare to its counterpart by common impregnation method, the light-off temperature over the catalyst by colloid synthesis method can be significantly decreased by 39 °C for CH4 and 27 °C for NO, respectively. The study may provide a general method to control the formation of metal (oxide) nanoparticles for heterogeneous catalysis, especially for emission abatement of NGVs.

Hydrogen generation by steam reforming of tar model compounds using lanthanum modified Ni/sepiolite catalysts

The paper describes the preparation of Ni/xLa-SEP catalysts selected low-cost clay minerals as support that possess high catalytic performance for steam reforming of phenol-ethanol (SRPE) to sustainably produce hydrogen. The catalysts were characterized using inductively coupled plasma optical emission spectrometry (ICP-OES), N2 adsorption-desorption, X-ray diffraction (XRD), H2 pulse chemisorption, high-resolution transmission electron microscopy (HRTEM), hydrogen temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the addition of La reduced the active metal size and increased the active metal surface of the Ni/SEP catalyst. The Ni/10La-SEP catalyst exhibited the smallest active metal size (5 ± 0.5 nm) and highest active metal surface area (12.7 m2/gcat.). As expected, Ni/10La-SEP presented the highest carbon conversion and H2 yield (92.1 and 87.6%, respectively) during SRPE reactions. Moreover, the La addition enhanced the steam reforming (SR) of CH4 and water-gas shift (WGS) reactions and successfully suppressed the sintering and coking of the Ni/SEP catalyst.

Preparation of carbon supported Pt-Ni alloy nanoparticle catalyst with high metal loading using cation exchange resin and its application for hydrogen production

Formic acid has been attracting interest as a promising hydrogen carrier because hydrogen can be produced over the catalysts under mild condition with low energy input. Though the catalytic activity for hydrogen production from formic acid is enhanced by increasing the metal loading, the trade-off between high metal loading and small metal particle size practically occurred with carbon catalyst prepared by impregnation method. To overcome this challenge, we herein utilized a noble catalyst preparation method which uses an ion-exchange resin as an initial carbon material. Five compositions of carbon supported Pt-Ni alloy catalysts were successfully prepared at high metal loading (25–50 wt%) with small metal particle sizes (2.3–3.8 nm observed by TEM). The metal particles were embedded in the carbon, which was contributed to small particle size of the loaded metal. The hydrogen production from formic acid was investigated over the prepared catalysts at 100–200 °C. It was elucidated that the turnover frequencies of Pt50Ni50/C and Pt75Ni25/C were higher than that of Pt/C at above 175 °C, suggesting that the decrease of Pt content without losing their catalytic activity could be achieved by Pt50Ni50/C and Pt75Ni25/C due to alloy formation. To further enhance the catalytic activity by increasing the active metal surface area, supercritical water treatment at 400 °C for 1 h was utilized. The metal surface area of catalysts was noticeably increased due to the gasification of the carbon support nearby metal particles. Formic acid conversion, likewise, drastically increased after the treatment.

Intensification of a hydrogenation catalyst activity by nanosecond pulsed discharge treatment

In this work, we report on a Johnson Matthey‐developed palladium (Pd)‐based catalyst activity enhancement using nanosecond pulsed discharge treatment. The impact of treatment energy via pulse voltage, pulse frequency, and treatment time individual variation on acetylene‐to‐ethylene hydrogenation reaction performance is investigated. Up to 11.2% increase in C2H2 conversion is attained after plasma treatment at specific treatment energy of 5340 J gcat−1, while C2H4 selectivity remains constant. To elucidate the effect of plasma on catalyst activity, characterization with SEM, BET, CO chemisorption, ICP‐MS, and XRD is carried out. C2H2 conversion increase is due to the higher active metal surface area attained after the plasma treatment. Other than the improved Pd surface area, not significant increase in specific surface area is observed, while even at high energy inputs no catalyst destruction occurs, as neither metal losses, nor phase changes are induced during plasma treatment.

Effect of Mg-modified mesoporous Ni/Attapulgite catalysts on catalytic performance and resistance to carbon deposition for ethanol steam reforming

A series of Mg-modified mesostructured Ni/Attapulgite (Ni/xMg-ATP, x = 0, 5, 10, and 20 wt%) have been produced by a co-precipitation method. The textural and physicochemical properties of as-prepared precursors and derived catalysts were characterized by N2 physical adsorption analysis, low- and wide- angle XRD, ICP-OES, H2 pulse chemisorption, SEM/EDX-mapping, TEM, FT-IR, H2-TPR and NH3-TPD. From N2 physical adsorption analysis, all synthesized catalysts possessed unique mesostructure, resulting in the high metal dispersion and interaction between active metal and support as proven by XRD, FT-IR, SEM/EDX-mapping, TEM, and H2-TPR. These properties became more distinct for Ni/10Mg-ATP sample, which had highest active metal surface area (0.69 m2/gcat) related to the smallest Ni crystal size (9.5 ± 0.1 nm), the most uniform nickel particle size and the highly dispersed Ni metal (20.2%), accompanying with highest nickel-ATP interaction. These excellent properties made it show the highest ethanol conversion (100%) and H2 yield (96.7%) and the longest stability (50 h), during ethanol steam reforming (ESR) under the T = 973 K, S/C = 1.5, and GHSV = 19,200–19,400 h−1. Meanwhile increasing temperature was positive effect for ethanol conversion and inhibiting the selectivity to hydrocarbon (such as CH4 and C2H4). In addition, the product selectivity was also considered to investigate the influence of Mg on catalytic performance. Obviously, the C2H4 selectivity (<1%), which was generally accepted as the precursor of coke deposition, was significantly decreased with the addition of Mg. It was related to the decrease of acidic strength on the catalyst surface, which resulted from the Mg introduction and was detected by NH3-TPD analysis. The spent catalysts after 50 h of ESR reaction were also investigated by XRD, SEM-EDX, TEM, and TG-DTG, the results suggested that the addition of Mg significantly suppressed the formation of filamentous carbon and the sintering of nickel particles, and further reduced the carbon deposition rate reduced to 6.1 mg·(gcat h)−1 over Ni/10Mg-ATP.

A sinter resistant Co Fischer-Tropsch catalyst promoted with Ru and supported on titania encapsulated by mesoporous silica

One of the pathways responsible for the deactivation of Fischer-Tropsch catalysts is the loss of active metal surface area due to nanoparticle agglomeration. To combat this effect efforts have been made to increase the interaction between the metal nanoparticles and the support using materials like silica. In this study, the supported metal particles were covered with a highly porous layer of silica to stabilize the Co nanoparticles on a titania support both during reduction and under reaction conditions. Co3O4 nanoparticles (size range: 8–12 nm) supported on titania were stabilized by coating them with a thin layer of mesoporous silica (∼4 nm) to make Fischer-Tropsch catalysts that are less prone to sintering (Co/TiO2@mSiO2). To mitigate the strong metal support interactions brought about by the titania and silica a Ru promoter was loaded together with the cobalt nanoparticles onto the titania (CoRu/TiO2@mSiO2). Temperature programmed XRD studies on the evolution of the Co metal nanoparticles showed that there was no significant particle size growth under reduction conditions in the temperature range from 30 to 600 °C. Chemisorption studies following reduction under hydrogen at 350 °C and 450 °C gave results consistent with the in situ XRD data when compared to the Co/TiO2. Fischer-Tropsch synthesis on the Co/TiO2@mSiO2 and CoRu/TiO2@mSiO2 catalysts encapsulated inside the mesoporous silica shell exhibited good catalytic performance without any display of significant mass transport limitations that might arise due to a silica shell coating of the active sites. For these two catalysts the Fischer-Tropsch activity increased with reduction temperature without any significant negative changes in their selectivity due to sintering, while the activity on Co/TiO2 decreased due to Co nanoparticle sintering.

Selective hydrogenation of biomass-derived ethyl levulinate to γ-valerolactone over supported Co catalysts in continuous process at atmospheric pressure

The present work is aimed to produce γ-valerolactone (GVL) from ethyl levulinate hydrogenation over non-noble metal cobalt catalysts at atmospheric pressure in continuous process. Various supported (SBA-15, SiO2, Al2O3, ZrO2, and TiO2) cobalt catalysts were prepared by wet impregnation method and characterized by XRD, N2 physisorption, SEM, TEM, NH3-TPD, H2-TPR and H2-pulse chemisorption techniques. The yield of GVL follows the trend Co/SBA-15>Co/SiO2>Co/Al2O3>Co/ZrO2>Co/TiO2 similar to trend in active Co metal surface area. The catalytic activity of the supported Co catalyst is strongly influenced by the dispersion and particle size of the Co.

Easy Preparation of Tannin‐Based Ag Catalysts for Ethylene Epoxidation

AbstractUltramicroporous carbons loaded with silver (Ag) nanoparticles were synthesised by submitting tannins to hydrothermal treatment in aqueous solutions of silver nitrate at different concentrations, followed by a pyrolysis step. The resultant materials were oxidised with dioxygen diluted in argon for removing the carbon partly coating the Ag nanoparticles and thus increasing the active metal surface area. Morphological, chemical, structural and textural characterisations were carried out in order to establish relationships between the physicochemical properties of the materials and their performances as catalysts for ethylene epoxidation. The latter reaction was increasingly promoted at higher silver content, and the efficiency of the oxidative post‐treatment was evidenced. The relation between selectivity and Ag content was nonlinear, in favour of the improved availability of silver nanoparticles after the removal of the carbon coating, at constant surface area and micropore size distribution of the carbon support. A favourable effect of Ag nanoparticles agglomeration on the selectivity was suggested.

The Effect of Temperature and Initial Methane Concentration on Carbon Dioxide Methanation on Ni Based Catalysts

Abstract A series of Ni based catalysts prepared by incipient wetness method were characterized by chemisorption and studied for CO 2 methanation. Ru had apparently a positive effect on the active metal surface area, and thus the catalytic activity. The CO 2 conversion was greatly affected by temperature where the conversion ranged from 12%-85% at temperatures of 300 to 400 o C on the 12% Ni/Al 2 O 3 catalyst. At 350 o C, higher Ni loading resulted in increased activity. The incorporation of 0.5% Ru lead to a drastic increase in catalytic activity, which can be explained by increased reducibility and a synergetic effect between Ni and Ru, and was further enhanced by increased Ni loading. Addition of CH 4 at twice the initial concentration of CO 2 to the feed gas mixture was found to decrease the conversion from 52% to 48% at 350 o C on the 20% Ni/Al 2 O 3 catalyst, whereas only a slight reduction in selectivity was observed. The results preliminary demonstrate that high methane purity can be achieved from a biogas feed stream over Ni based catalysts.

Effect of the support on physicochemical properties and catalytic performance of cobalt based nano-catalysts in Fischer-Tropsch reaction

In this paper, comparative investigations of the effects of CNTs and γ-Al2O3 on the physicochemical properties and catalytic performances of Co based nano-catalyst during FTS have been presented. Catalysts were prepared via a wet impregnation method and characterized by various analytical techniques such as transmission electron microscopy (TEM), temperature programmed reduction (H2-TPR), carbon dioxide temperature programmed desorption (CO2-TPD) and X-ray photoelectron spectroscopy (XPS). Fischer-Tropsch reaction (FTS) was carried out in a fixed-bed microreactor (220°C and 1atm and with H2/CO=2v/v, SV of 12L/gh). Various characterization techniques revealed that Co nanocatalysts supported on CNTs and Al2O3 were different in physicochemical properties. There was a stronger interaction between Co and Al2O3 support compared to that of CNTs support. CNTs support increased the reducibility, dispersion, active metal surface area and decreased Co particle size. A significant increase in% CO conversion and FTS reaction rate was also observed over CNTs support compared to that of Co/Al2O3. Co/CNTs resulted in higher C5+ hydrocarbons selectivity compared to that of Co/Al2O3 catalyst.

Ag supported on meso-structured SiO2 with different morphologies for CO oxidation: On the inherent factors influencing the activity of Ag catalysts

With the objective to prepare better CO oxidation catalysts and explore the inherent factors to determine the activity of supported Ag catalysts, KCC-1, SBA-15 and MCM-41, a series of mesoporous SiO2 with different morphologies, have been synthesized and used as supports for Ag to prepare catalysts (7% Ag/KCC-1, 7% Ag/SBA-15 and 7% Ag/MCM-41) for CO oxidation. It is found that the morphologies of the SiO2 supports influence the dispersion of the supported Ag species, thus resulting in catalysts with different Ag grain sizes and active metallic surface areas, as proved by XRD and H2 adsorption-desorption results. With fibrous KCC-1 silica spheres as the support, the mobilization and aggregation of the Ag particles can be effectively hindered by the open access surface mesopores. Therefore, compared with SBA-15 and MCM-41, Ag nanoparticles with much smaller grain sizes have been achieved, thus resulting in a catalyst with significantly improved activity. Furthermore, a linear relationship has been found between the differential CO oxidation rates and the Ag grain size. Therefore, it is concluded that the active Ag metal surface area is the determining factor for the activity of the silica supported Ag catalysts.

Nature of Active Sites and Their Quantitative Measurement in Two-Dimensional Pt Metal Catalysts

Quantitative measurement of the number of active surface sites on two-dimensional (2D) catalysts is one of the most crucial points in heterogeneous catalysis because it is used to determine the turnover frequency (TOF), which refers to the catalytic activity of model catalysts. However, because of the difficulty in identifying the effective active surface area on 2D heterogeneous catalysts, there is still the assumption that each metal atom is an active site. To shed light on these issues and to bridge the activity gaps between 2D and three-dimensional (3D) heterogeneous catalysts, we present an experimental approach that uses Pt nanoparticle (NP) arrays on a thin silicon wafer probed with CO pulse chemisorption, a widely used surface-sensitive technique, to determine the number of active sites and the area of the effective active surface. A Pt thin film and Pt NP arrays with two different NP sizes (i.e., 2.1 and 4.5 nm) were prepared as model systems for 2D catalysts. The effective active metal surface area determined using CO pulse chemisorption for these 2D catalysts is 53–79% of the apparent metal surface area that was obtained by measuring the surface area based on scanning electron microscopy images. This discrepancy between the active and apparent surface area is attributed to the presence of hydrocarbon contamination and organic capping layers on the catalysts. The results indicate that estimating the active sites of 2D catalysts by apparent surface area is reasonably in agreement with the number measured by chemisorption that is used to characterize 3D nanocatalysts. This experimental technique on 2D catalysts can be expected to provide information for extracting the true TOF of product molecules on 2D catalysts in gas-phase catalytic reactions.

Fischer-Trospch Synthesis on Ordered Mesoporous Cobalt-Based Catalysts with Compact Multichannel Fixed-Bed Reactor Application: A Review

CO hydrogenation to hydrocarbons through Fischer–Tropsch synthesis (FTS) reaction is one of the promising chemical processes, which can convert alternative feedstocks such as natural gas or biomass into synthetic fuels. The FTS reaction has received many attentions due to a limited petroleum resource with an increased demand for using alternative carbon sources such as stranded gas or shale gas. Some proper synthetic methods of an effective FTS catalyst having a larger active metal surface area and a lower deactivation rate are the most important issues for a long-term operation. Therefore, some ordered mesoporous materials (OMM) have been widely investigated in the field of CO hydrogenation using some heterogeneous catalysts. The present brief review paper summarized the various preparation methods of the ordered mesoporous materials for the possible applications of FTS reaction with a lower deactivation rate and a higher catalytic performance. The applications of the ordered mesoporous cobalt oxides for FTS reaction are briefly introduced and the ways to improve a structural stability even under reductive CO hydrogenation conditions by using efficient pillaring materials as well as by preparing mixed metal oxides. A higher catalytic activity of the ordered mesoporous cobalt oxide was also verified in a multi-channel fixed-bed compact reactor having the intersected interlayers of micro-channel heat exchanger. The thermal stability of ordered mesoporous cobalt-based catalysts was mainly affected by a structural stability which can easily remove the heavy hydrocarbons from the inner surfaces.

Aqueous phase reforming of glycerol using highly active and stable Pt0.05CexZr0.95-xO2 ternary solid solution catalysts

The aqueous phase reforming (APR) of glycerol is an attractive yet challenging pathway to convert abundant biomass into value added hydrogen. Pt catalysts have received attention due to their ability to produce hydrogen-rich gas under APR conditions. In this work, the conversion of glycerol into hydrogen is demonstrated using Pt0.05CexZr0.95-xO2 (x=0, 0.29, 0.475, 0.66 and 0.95) solid solution catalysts. Both characteristic (XRD, BET, H2-TPR, CO-chemisorption, TEM and XPS) and reactivity measurements were used to investigate the activity of the catalysts. Results indicated that reactivity depended on the Ce/Zr ratio, which in turn affected the Pt oxidation state, active metal dispersion and surface area, and particle size. Among these catalysts Pt0.05Ce0.475Zr0.475O2 showed the highest carbon to gas conversion (95%), highest H2 yield (93%), highest H2 selectivity (98%) and at least 50h of stability. The overall catalytic performance decreased in the order Pt0.05Ce0.475Zr0.475O2>Pt0.05Ce0.29Zr0.66O2>Pt0.05Zr0.95O2>Pt0.05Ce0.66Zr0.29O2>Pt0.05Ce0.95O2.

Enhancing Ni-SiO2 catalysts for the carbon dioxide reforming of methane: Reduction-oxidation-reduction pre-treatment

The work presented here evaluated the impact of reduction-oxidation-reduction (ROR) pre-treatment on 5 and 10% Ni-SiO2 as an efficient and inexpensive manner of enhancing catalysts for the carbon dioxide reforming of methane. Samples were reduced, oxidised and subsequently re-reduced, with the Ni deposit characteristics being analysed at each step. It was demonstrated that ROR treatment decreased the average Ni deposit size and altered the interaction between the Ni and SiO2, which significantly enhanced catalytic performance. ROR pre-treatment resulted in an increase in CH4 conversion, most significantly for the 10% Ni-SiO2 samples (from 57% to 69% at 800°C) with comparable carbon formation between the reduced and ROR pre-treated samples. During 600°C stability tests the 10% reduced samples deactivated, due to carbon build-up, after 3–4h reaction time. In contrast, at 600°C the ROR sample maintained stable conversion after 6h over a 12h time frame. Additionally, for all samples ROR pre-treatment resulted in a more stoichiometric H2/CO ratio. The reduction in both Ni deposit size and crystallinity increased conversion and selectivity. This derived from a greater active metal surface area for conversion as well as a decrease in the prevalence of methane decomposition and the reverse water gas shift reaction by influencing the desorption of CO and lowering the occurrence of bulk NiO. Ultimately, ROR pre-treatment provides a simple and inexpensive means of improving dry reforming catalysts.

Carbon covered Mg–Al hydrotalcite supported nanosized Ru catalysts for ammonia synthesis

Carbon covered hydrotalcite (CCHT) supported Ru catalysts with single (Cs or Ba) and double (Cs and Ba) promoters were prepared by two different methods viz., impregnation (IMP) and polyol reduction (PR) methods using ethylene glycol as solvent. The performance of the catalysts for ammonia synthesis was carried out in the temperature range of 523–698K at atmospheric pressure. The following sequence with respect to the % NH3 (volume/volume) formation was observed; BaRuCCHT-IMP<BaRuCCHT-PR<CsBaRuCCHT-IMP<CsRuCCHT-IMP<CsRuCCHT-PR<CsBaRuCCHT-PR. XRD, TEM, N2-adsorption, H2-TPR, CO chemisorption and TPD of H2 and CO2 techniques were used to investigate the physico-chemical properties of the catalysts and also to establish the reasons responsible for superior catalytic activity of CsBaRuCCHT-PR catalyst. The CO chemisorption and TEM studies revealed that CsBaRuCCHT-PR catalyst possessed the high active Ru metal surface area and small particle size. The highest activity of this catalyst could be attributed to high surface area, low particle size, high active surface metal (Ru) area, and strong Ru–CCHT interaction.