Ni Crystallite Size Research Articles

Insight and comprehensive study of Ni-based catalysts supported on various metal oxides for CO2 methanation

In this study, nickel supported on various metal oxides were prepared by simple impregnation and the performance for CO2 methanation was tested. The oxide supports were all prepared by thermal decomposition of metal salts to provide comparable oxide properties such as surface area. Among the investigated oxides, nickel supported on CeO2 and Y2O3 showed the highest CO2 conversion of 90% at 320 °C with highest CH4 selectivity of 99%. The order of catalyst activity (XCO2@320°C) was reported: Ni/CeO2 ~ Ni/Y2O3 > > Ni/La2O3 > Ni/ZrO2 > Ni/Al2O3 > Ni/MgO > Ni/CaO > > Ni/MnO. The physicochemical properties of the catalysts were analyzed by TEM, BET, XRD, ICP, H2-TPR, CO2-TPD, H2 chemisorption, TGA, Raman, and XPS. From the characterization results, the catalyst activity was independent to specific surface area of catalyst and crystallite size of Ni. The amount of oxygen vacancies and weak-to-medium basic sites exhibited major roles for enhancing catalyst activity. The CeO2 and Y2O3 as reducible oxide supports not only provided abundant oxygen vacancies / basic sites, but also promoted Ni dispersion with appropriate interaction between metal and support, resulting in higher reducibility at low temperature. The reduction of catalyst at high temperature can significantly improve the performance of Ni supported on non-reducible MgO. However, the Ni/CeO2 and Ni/Y2O3 reduced at high temperature suffered from coalescence of CeO2 and Y2O3, though Ni crystallite sizes are well preserved from sintering.

Impact of nickel and alkaline earth metals interaction on sustainable carbon nanotubes generation from plastic face masks via catalytic pyrolysis

The one-pot synthesis of carbon nanotubes (CNTs) emerges as a promising approach for plastic valorization, owing to its simplicity and scalability. However, limited attention has been given to catalyst design for this method, particularly regarding the influence of Group 2 alkaline earth metal elements (X) on the Ni-based catalyst activity. This study investigates the impact of X on the catalytic activity of Ni towards sustainable CNTs synthesis using plastic face masks. The findings revealed that X influenced the carbon yield of NiMo-X catalysts and the morphology of the resultant carbon nanomaterials. Notably, NiMo-Ca demonstrated the highest carbon yield, whereas NiMo-Mg and NiMo-Ba exhibited the lowest. Furthermore, NiMo-Mg tends to produce clean and thin CNTs, while NiMo-Ba tends to yield carbon flakes with numerous irregular cokes. In addition to the effect of Ni crystallite size, which influences the transition from tubular to flake-like carbon structures, environmental factors are also considered. Specifically, NiMo-Mg generated a high CO2/CH4 environment, while NiMo-Ba exhibited slower catalytic cracking of polymeric chains from face masks, both of which were unfavorable for CNTs growth. Conversely, NiMo-Ca facilitated higher carbon recovery, likely due to its creation of a low CO2/CH4 environment via CO2 methanation. Optimization studies indicated that increasing pyrolysis temperatures and durations lead to reduced carbon yield, while cyclic pyrolysis of face masks up to five iterations enhances the reusability of NiMo-X catalysts with improved carbon recovery. Overall, this study provides valuable insights into the early pyrolytic gas formation and carbon nucleation phase, which are influenced by the surface Ni fraction and Ni polarization, as well as the later CNTs growth phase, which is related to the Ni crystallite size.

Biogas dry reforming over Li–Ni–Al LDH-derived catalysts

Biogas dry reforming or dry reforming of methane (DRM) is an alternative to produce hydrogen, in the context of development of sustainable routes for energy production, since this route uses CH4 and CO2, two greenhouse gases as reactants. However, the deactivation of catalysts due to carbon deposition and sintering is the main drawback of this reaction. In this work, with the aim of minimizing carbon formation and sintering during DRM, the effect of lithium as a promoter in catalysts Ni–Al derived from layered double hydroxides was investigated. The catalysts were prepared by co-precipitation and characterized by different techniques: BET surface area (SBET), X-ray diffraction (XRD), temperature-programmed reduction (TPR), CO2 and H2 temperature-programmed desorption (CO2-TPD and H2-TPD), Scanning Electron Microscopy (SEM-EDS), temperature-programmed oxidation (TPO). The catalytic tests were carried out in a fixed bed reactor using a synthetic biogas (60% CH4 and 40% CO2) in the temperature range of 500–750 °C. The incorporation of Li into the Ni–Al-LDH changed the reducibility and basicity of the catalysts. The Li2 sample containing an intermediary amount of Li (5 wt%) showed the highest reduction temperature and highest density of basic sites, which resulted in the smallest Ni crystallite size before and after the reactions. As a result, this catalyst presented the greater resistance to sintering and a lower rate of carbon produced. For the reaction carried out at 700 °C, only the Li2 catalyst remaining active during the test and reaching a maximum of 80% and a final CH4 conversion of 54% after 480 min of reaction, whereas CO2 conversion was higher than 90%. All other samples deactivated at different rates due to carbon deposition and sintering.

Nickel catalyst supported on SiC incorporated SiO2 for CO2 methanation: Positive effects of dysprosium promoter and microwaves heating method

In this work, Dy-promoted Ni/SiC-SiO2 catalysts with varied Dy loadings (0–1 %) were developed using the wet impregnation method and evaluated for their effectiveness in CO2 methanation. The characterization results reveal that Dy addition can reduce the Ni crystallite size, enhance the dispersion of active phase and increase the catalyst’s reducibility. Among the prepared catalysts, the 0.5 %Dy-10 %Ni/SiC-SiO2 demonstrated the highest CH4 selectivity (100 %) and CO2 conversion (73.9 %) at 350 °C owing to its highest basic sites and H2 chemisorption capacity. The performance of this Dy-promoted catalyst diluted with different amounts of SiC, which was employed as a microwave susceptor and high thermal conductive dilution material, was also investigated in both microwave and electric reactor. Microwave heating leads to higher CO2 conversion compared to electric heating, regardless of reaction temperature and dilution factor due to selective heating and the random occurrence of hot spots, which are usually considered as micro-plasmas in the catalyst bed. However, further increase quantity of SiC decreased both CO2 conversion and CH4 selectivity regardless of heating method. This may be attributed to the appearance of extreme overheating and the absence of gentle overheating with increased amount of SiC in the microwave and electric reactors, respectively. The temperature-programmed oxidation results demonstrated that carbon deposition on the 0.5 %Dy-10 %Ni/SiC-SiO2 catalyst during 30 h of reaction can be significantly suppressed by microwave.

An Evaluation of the Wear Resistance of Electroplated Nickel Coatings Composited with 2,2,6,6-Tetramethylpiperidine 1-oxyl-Oxidized Cellulose Nanofibers.

In this study, the wear resistance of nickel (Ni)-cellulose nanofiber (CNF) composite electroplated films on steel plates (JIS SPCC, cold-rolled steel) was evaluated, including their surface and microstructural properties. In the CNF sample, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-oxidized CNF was used. As a result of the ball-on-disk abrasion test, in which steel (SUJ2) balls were used as the counterpart material, the plated film obtained with the addition of 1 g/L of CNF to the plating solution showed the highest wear resistance in this study. Compared to the conventional Ni-plated film without CNF, the abrasion loss volume on the plated side was reduced by approximately 79%, and that on the ball side was reduced remarkably by 94%. A microstructural analysis of the abrasion scars showed areas where co-deposited CNFs were stretched in the direction of abrasion, suggesting that the wear reduction effect was caused by sliding between the individual CNFs within the aggregates. Moreover, the hardness of the plated film increased when the Ni crystallite size became finer. It was confirmed that the co-deposition of fine CNFs is effective in improving hardness, whereas the co-deposition of a certain degree of aggregated CNFs is effective in exhibiting the wear reduction effect.

Partial hydrogenation of 1,3-butadiene over nickel with alumina and niobium supported catalysts

The hydrogenation of 1,3 butadiene (BD) is an important industrial process that is generally used to generate butenes and aromatics, which are important petrochemicals and constituents of transportation fuels. Ni-based catalysts have gained increasing interest in the academic community and industry because of their superior hydrogenation activity, ability to exist in multiple oxidation states and most importantly, affordability compared to the less-abundant precious metal catalysts. In this work, we explore the ability of alumina (Al2O3) and niobia (Nb2O5) as catalytic supports for Ni as the active metal since they have shown excellent potential for hydrogenation of alkenes. Specifically, we compare the metal-support interactions, which disperse Ni effectively throughout the catalyst surface, textural and pore parameters, Ni crystallite size, surface morphology, elemental composition, coke formation and tendencies of both catalysts through extensive characterization techniques such as H2-temperature programmed reduction (H2-TPR), N2-adsorption–desorption, X-ray diffraction (XRD), scanning electron microscopy combined with electron-dispersive spectra (SEM-EDS), and thermal analysis of the spent catalysts. Limited reports on the use of niobium oxides and alumina as supports for Ni in the partial hydrogenation of BD prompted us to explore this literature gap. The catalytic reactions were conducted using a quartz tube reactor between a temperature range of 50 and 400 °C at regular intervals of 50 °C under operating pressures of 1 atm. A comprehensive analysis of the products from the reaction was carried out using gas-chromatography with mass spectrometry (GC–MS) detector and corroborated these results with those from infrared spectroscopy (FTIR). Reaction mechanisms of aliphatic and aromatic product formation were proposed and verified with literature and our own characterization results. The tests on the spent catalysts also helped to reveal the extent of deactivation of the catalysts due to carbon deposition. Mechanisms of catalyst deactivation and nature of carbonaceous deposits were explored and elaborate scientific reasoning was provided as to why Ni/alumina showed better performance in terms of product yields and BD conversion. Ways to mitigate the harmful effects of coke formation and its deposition are also discussed. The novelty of our work is that a comprehensive comparison of the performance of Ni/alumina and Ni/niobia for hydrogenation of BD along with extensive discussions on coke formation, its chemical nature and proposed reaction chemistry based on obtained characterization results of the catalysts and the products of BD hydrogenation has not been done before for this system. In this way, we show the low-temperature conversion of BD represents an economically efficient and relatively simple method to convert toxic, carcinogenic and environmentally hazardous BD into high-value products using low-cost and chemically efficient catalysts.

Oxidative steam reforming of acetic acid on Ni catalysts: Influence of the La promotion on mesostructured supports

In this work, the support effect and the La2O3 promotion of Ni-based catalysts on the oxidative steam reforming of acetic acid as bio-oil model compound has been studied. Ni/SBA-15 showed the worst catalytic performance with an acetic acid conversion dropping below 30% at 500 °C ascribed to active phase oxidation. In contrast, Ni supported over mesoporous CeO2 (CeO2-m) reached better catalytic performance and lower coke formation due to the higher Ni dispersion and oxygen mobility of the support. On the other hand, La2O3 promotion to SBA-15 and CeO2-m led to even higher Ni dispersion and prevented sintering during the reforming reaction. This effect resulted in an improvement in the catalytic performance for both promoted samples. As a consequence of low Ni crystallite size and high oxygen mobility, Ni/La2O3–CeO2-m reached almost complete conversion (∼96%), the highest hydrogen yield (∼53%) maintained for 5 h with the lowest coke formation (62.3 mgcoke·gcat−1·h−1).

Sustainable syngas production by oxy-steam reforming of simulated biogas over NiCe/MgAl hydrotalcite-derived catalysts: Role of support preparation methods on activity

Herein, a series of hydrotalcite-derived MgAl supports were prepared by co-precipitation and hydrothermal methods. NiCe/MgAl catalysts were prepared by loading Ni (10 wt%) and Ce (2.5 wt%) on supports using sequential incipient wetness impregnation and tested in oxy-steam reforming of simulated biogas to produce syngas. N2-physisorption, XRD, XPS, SEM, TEM, ICP-OES, TGA, and Raman were used for catalyst characterization. Reactivity was evaluated at 600 °C, 700 °C, and 800 °C with a constant GHSV (45,000 ml gcat−1 h−1) and feed ratio (CH4/CO2/O2/H2O = 1/0.67/0.1/0.3). The results demonstrate that increasing the co-precipitation aging temperature and the hydrothermal reaction temperature affected the surface area, pore volume, and Ni crystallite size. However, no significant change in reactivity was observed. The NiCe/MgAl catalyst with co-precipitation aging temperature of 140 °C (NCMA140-Co) exhibited lower carbon deposition probably due to higher Ce4+ concentration. Therefore, NCMA140-Co provided high stability and conversions of CH4 (94%) and CO2 (82%) with H2/CO ratio (1.6) at 800 °C without carbon deposition.

Inclusion of W in electroless Ni–B coating developed from a stabilizer free bath and investigation of its tribological behaviour

In the present study, tribological and corrosion behaviour of electroless Ni–B–W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 °C, 90 °C, and 95 °C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 °C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV100 at bath temperatures of 85 °C, 90 °C, and 95 °C respectively. The inclusion of W to Ni–B coating enhanced the hardness by ∼150 HV100. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 °C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 °C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.

Influence of silica promotion on NiCe/MgAlSi catalysts for the oxy-steam reforming of biogas to syngas

This work has exploited the effects of silica on magnesium aluminum silicate supported NiCe based catalysts (NiCe/MgAlSi) prepared using sol-gel method followed by incipient wetness impregnation for syngas production through oxy-steam reforming (OSR) of biogas. Measurements investigating the effects of increasing Si/Al molar ratio (0–5) on activity and carbon deposition were performed in a once-through flow reactor at atmospheric pressure and temperatures of 600, 700, and 800 °C with a fixed GHSV of 45,000 ml gcat−1 h−1 and molar feed ratio of CH4/CO2/O2/H2O = 1/0.67/0.1/0.3. The catalysts were characterized by N2-physisorption, XRD, SEM, HRTEM, TGA, Raman, and ICP-OES. In the results, the addition of silica has been found to increase Ni crystallite sizes and decrease carbon deposition. Thus, NiCe/MgAlSi with Si/Al = 5 is promising, exhibiting high conversions of CH4 (91.7%), CO2 (80.4%), and H2/CO ratio of 1.6 without carbon deposition and good stability for 120 h at 800 °C.

Investigating the Effect of Ni Loading on the Performance of Yttria-Stabilised Zirconia Supported Ni Catalyst during CO2 Methanation

CO2 methanation was studied on Ni-based yttria-stabilised zirconia (Ni/YSZ) catalysts. The catalysts were prepared by the wet impregnation method, where the amount of Ni content was varied from 5% to 75%. Thereafter, the prepared catalysts were analysed by BET, XRD, SEM and H2-TPR. BET results showed an initial increase in the surface area with an increase in Ni loading, then a decrease after 30% Ni loading. The XRD results revealed that the Ni crystallite size increased as the Ni loading increased, while the H2-TPR showed a shift in reduction peak temperature to a higher temperature, indicating that the reducibility of the catalysts decreased as the Ni loading increased. The activity of the synthesised catalysts for CO2 methanation was studied by passing a mixture of H2, CO2 and N2 with a total flow of 135 mL min−1 and GHSV of 40,500 mL h−1 g−1 through a continuous flow quartz tube fixed-bed reactor (I.D. = 5.5 mm, wall thickness = 2 mm) containing 200 mg of the catalyst at a temperature range of 473 to 703 K under atmospheric pressure and a H2:CO2 ratio of 4. The tested Ni/YSZ catalysts showed an improvement in activity as the reaction temperature increased from 473 K to around 613 to 653 K, depending on the Ni loading. Beyond the optimum temperature, the catalyst’s activity started to decline, irrespective of the Ni loading. In particular, the 40% Ni/YSZ catalyst displayed the best performance, followed by the 30% Ni/YSZ catalyst. The improved activity at high Ni loading (40% Ni) was attributed to the increase in hydrogen coverage and improved site for both H2 and CO2 adsorption and activation.

Effects of oxidation degree of support and phosphorus modification on the catalytic cracking of coal pyrolysis tar by char-supported nickel catalysts

The low rank coal can be converted efficiently when it undergoes the pyrolysis process. The utilization of tar is modified and the problems such as pipeline blockage are solved by cracking and lightning heavy components in tar. In this study, the char-supported nickel (Ni) catalysts were prepared by different Ni loading methods, and the cracking of coal pyrolysis tar was improved by the coal char support with different oxidation degrees. The catalysts prepared by ion exchange method showed better performance for the tar cracking than other methods, which is related to their smaller Ni crystallite size (NCS). The oxidation of H2O2 and HNO3 significantly increased the number of oxygen-containing groups. The intrinsic correlation between oxidation degree of support and catalytic property indicated that the XH2O2-Ni/C (ZD coal pretreated by H2O2) series catalysts had better tar cracking activity than XHNO3-Ni/C (ZD coal pretreated by HNO3) series catalysts, which did not only depend on the increase of Ni loading amounts but also related to the smaller NCS and higher dispersion. Moreover, the non-metallic additive phosphorus (P) was added to modify the catalysts. It was found that the addition of P significantly improved the tar cracking performance of the 30%H2O2 P-Ni/C catalyst. The amounts of active components loaded and NCS contributed to the production of light tar.

Effect of Metal Dopant on the Performance of Ni@CeMeO2 Embedded Catalysts (Me = Gd, Sm and Zr) for Dry Reforming of Methane

Biogas upgrading by a catalytic process has been studied in order to obtain syngas using renewable source of methane. This work evaluates the influence of metal dopant (Gd, Sm, and Zr) on the CeO2 structure for the dry reforming of methane over Ni nanoparticle embedded catalysts. The doping with Zr improved the thermal stability of the catalyst, leading to the formation of small Ni nanoparticles, while Ni metal sintering was observed for Ni@CeO2, Ni@CeGdO2, and Ni@SmO2, according to in situ XRD under reduction conditions. The ceria reducibility was affected by the dopant nature, for which the addition of Zr caused distortions in the ceria lattice, promoting the diffusion of oxygen bulk to surface. The doping with Gd and Sm created oxygen vacancies by charge compensation, and the saturation of oxygen vacancies in the fresh samples decreased the degree of Ce reduction, according to TPR results. The larger Ni particles and poor redox behavior for Ni@CeGdO2 and Ni@CeSmO2 were responsible for the high carbon formation on these catalysts during the DRM reaction. The Ni@CeZrO2 catalyst did not present coke formation because of smaller Ni crystallite size and higher ceria reducibility. Therefore, the control of Ni particle size and the high oxygen mobility in the Ni@CeZrO2 catalyst inhibits carbon deposition and enhances the mechanism of carbon removal, promoting the catalyst stability.

Effect of surface properties of Ni-MgO-Al2O3 catalyst for simultaneous H2 production and CO2 utilization using dry reforming of coke oven gas

We designed the customized Ni-MgO-Al2O3 catalyst for the dry reforming of methane (DRM) using coke oven gas (COG). The calcination conditions of the catalysts were systematically controlled to investigate the effect of the surface properties of the catalysts on catalytic performance. The characterization results showed that the physicochemical properties of the catalyst, such as basicity, BET surface area, Ni dispersion, Ni crystallite size, and reducibility varied with the calcination temperature. Considering the gas composition of the COG, the operating conditions were also optimized by calculating thermodynamic equilibrium to maximize the CO yield and minimize carbon deposition. As a result of catalytic evaluations conducted at selected operation conditions, we found that the catalytic activity is strongly affected by the number of Ni active sites correlated with the Ni dispersion and reduction degree. In addition, the basicity of the catalyst played an important role in CO2 adsorption and activation, which is related to coke resistance. Among the prepared catalysts, the Ni-MgO-Al2O3 (calcination temperature = 800 °C) catalyst exhibiting best catalytic performance due to a large number of Ni active sites and relatively good basicity, was selected as the optimal catalyst, and the possibility of commercialization was confirmed through the long-term stability test and start-up/shut-down test.

Ni-Al mixed metal oxide with rich oxygen vacancies: CO methanation performance and density functional theory study

Ni-Al mixed metal oxides have been successfully prepared by high shear mixer (HSM) and coprecipitation (CP) methods for low temperature CO methanation. In this work, Ni-Al (HSM-CP) catalyst presented small Ni crystallite size and high surface area, which all contribute to the methanation reaction at low temperature conditions. The obtained Ni-Al (HSM-CP) sample exhibited a mass of defective oxygen, thereby accelerating the dissociation of CO and ultimately increasing the activity of the catalyst. Ni-Al (HSM-CP) catalyst offered the best activity with CO conversion = 100% and CH 4 selectivity = 93% at 300 °C, and the CH 4 selectivity can reach 81.8% at 200 °C. In situ Fourier transform infrared spectroscopy and density functional theory show that CHO and COH intermediates with lower activation energy barriers are produced during the reaction, and hydrogen-assisted carbon–oxygen bond scission is more favorable.

Hydrogen production from ammonia decomposition over Ni/CeO2 catalyst: Effect of CeO2 morphology

Ammonia (NH3) decomposition to release COx-free hydrogen (H2) over non-noble catalysts has gained increasing attention. In this study, three nanostructured CeO2 with different morphologies, viz. rod (R), sphere (Sph), and spindle (Spi), were fabricated and served as supports for Ni/CeO2 catalyst. The CeO2 supports are different in particle sizes, specific surface area and porosity, resulting in the formation of Ni nanoparticles with distinguished sizes and dispersions. The surface properties of the Ni/CeO2 catalysts are not only distinct but also influential, affecting the adsorption and desorption of NH3, N2, and/or H2 molecules. The Ni/CeO2-R catalyst shows superior catalytic activity compared to the other two, owing to its smaller Ni crystallite size and larger BET surface area. The most abundant strong basic sites are observed for Ni/CeO2-Spi catalyst based on its exposed CeO2(110) planes, which facilitates the donation of electrons to the Ni particles, benefiting the associative desorption of N atoms. Thus, Ni/CeO2-Spi shows higher catalytic activity than Ni/CeO2-Sph, despite their almost identical Ni crystallite sizes.

Self-combustion Ni and Co-based perovskites as catalyst precursors for ammonia decomposition. Effect of Ce and Mg doping

LaCo1-xNixO3 perovskites have been synthesized by self-combustion, characterized, and examined as catalyst precursors for the COx-free hydrogen production from catalytic ammonia decomposition at low temperatures. The influence of the cobalt content as well as the addition of two dopant in different amount was studied and optimized. Small Ni crystallite size and high total basic sites were found to remarkably enhance the catalytic activity. Moreover, bimetallic perovskites generated cobalt/nickel in higher size, higher impurities and lower active sites than pure nickel perovskite, which decreased the ammonia conversion. On the other hand, the addition of dopant in adequate amount over pure Ni perovskite (La0.1A0.9NiO3; A = Ce or Mg) generated catalyst with low nickel crystallite size and high basicity delivering superior catalytic performance. Catalysts were demonstrated to be stable for at least 40 h. In fact, 96 % and 98 % ammonia conversion were achieved at low temperature (400 °C), when La0.1Ce0.9NiO3 and La0.1Mg0.9NiO3 were employed, resulting from the synergic effect between La-Ce and Ni-Mg-La. Presenting the Mg-doped perovskite the highest catalytic activity at the mild temperature of 350 °C.This study provides new insight in designing diverse catalyst precursors to develop economic and efficient catalysts to achieve high ammonia conversion (high hydrogen production) at low temperature and enhance the ammonia perspective as hydrogen carrier toward the ‘hydrogen economy’.

Mechanical and Tribology Properties of Electrodeposited Ni-TiN/Si<sub>3</sub>N<sub>4</sub> Composite Coatings

Ni-TiN/Si3N4 composite coatings on tungsten carbide were prepared by electrodeposition. The influences of electrodeposition temperature at 35 – 45 °C on coating microstructure and its impact to the mechanical and tribology properties were investigated to optimize the process parameter. A compact morphology of coatings gradually increased with increasing electrodeposition temperature that was addressed to the finer Ni crystallite size which resulted from co-deposition of TiN and Si3N4 particles. The finer crystallite size caused the increase of coating hardness with the highest (8.86 GPa) was achieved for the sample deposited at 45 °C. However, from the result of wear rate test, it was shown that the lowest wear rate (28.5 μm) was observed on the sample deposited at 40 °C.

Enhanced syngas production from glycerol dry reforming over Ru promoted -Ni catalyst supported on extracted Al2O3

Crude glycerol, a by-product of biodiesel production, has drawn considerable attention to the importance of glycerol valorization through dry reforming reaction to obtain syngas. The selection of suitable catalysts is significantly important to enhance the catalytic activity in glycerol dry reforming (GDR) reactions. Hence, Ru with different loadings (i.e. 1%, 2%, 3%, 4%, 5%) doped in 15% Ni-extracted Al2O3(EA) was evaluated as catalyst via GDR process in this study. The catalyst prepared by ultrasonic-impregnation assisted technique was subjected to 8 h of CO2 reforming of glycerol. The reactant conversions and products yield was in the order of 3%Ru-15%Ni/EA > 5%Ru-15%Ni/EA > 4%Ru-15%Ni/EA > 2%Ru-15%Ni/EA > 1%Ru-15%Ni/EA > 15%Ni/EA, while the quantity of carbon deposited was in the order 15%Ni/EA > 1%Ru-15%Ni/EA > 2%Ru-15%Ni/EA > 4%Ru-15%Ni/EA > 5%Ru-15%Ni/EA > 3%Ru-15%Ni/EA. 3%Ru-15%Ni/EA attained the greatest glycerol conversions of 90%, H2 yield of 80% and CO yield of 72% with the lowest carbon deposition of 7.38%. The dispersion of Ni particles on EA support evidently improved after the promotion step with Ru, which minimized the agglomeration of Ni and smaller crystallite size. In addition, the introduction of Ru increased the oxygen storage capacity which significantly reduced the formation of carbon during the reaction. GDR's optimal reaction temperature obtained over 3%Ru-15%Ni/EA catalysts was at 1073 K (i.e. 93% glycerol conversion; 87% H2 yield; 79% CO yield). Over a 72 h time on stream at 1073 K, 3%Ru-15%Ni/EA catalyst had superior catalytic activity and stability. Overall, 3%Ru-15%Ni/EA catalyst was more coke-resistant than other promoted catalysts due to its accessible structure, higher oxygen storage capacity, moderate basicity, uniformly dispersed Ni phase and stronger Ru/Ni-EA interaction.

Controlling carbon formation over Ni/CeO2 catalyst for dry reforming of CH4 by tuning Ni crystallite size and oxygen vacancies of the support

This work investigates the effect of Ni crystallite size and oxygen vacancies of the support on the formation of carbon over Ni/CeO2 catalysts for dry reforming of methane at 1073 K. A large crystallite size variation is achieved by using different Ni loading (5 and 10 wt%) and calcination temperatures (673, 873, 1073 and 1473 K). In situ XRD and XANES experiments reveal that the increase in calcination temperature increases the Ni crystallite size, whereas the amount of oxygen vacancies decreases. The amount of carbon formed during DRM increases as Ni crystallite size increases, achieving a maximum at around 20−30 nm and then, it continuously decreases. However, carbon deposition is negligeable below 10 nm and above 100 nm. For the catalysts with very large Ni crystallite sizes, the CH4 dissociation rate is likely so low that carbon species formed reacts and carbon accumulation does not take place. However, the oxygen vacancies of ceria do not contribute to the carbon removal from the Ni surface due to the low metal-support interface on these large Ni particles.