Temperature-programmed Oxidation Analysis Research Articles

Nickel nanocatalyst on lanthanum aluminate: Optimizing preparation and evaluating performance in glycerol dry reforming for syngas production

In this study, mesoporous nanocrystalline Ni/La-Al catalysts with varying nickel (Ni) loadings (5, 10, 15, and 20 wt.%) were synthesized using a solid-state method for the glycerol dry reforming (GDR) reaction. The effects of different Ni loadings and the addition of steam on the structural and catalytic performance of the catalysts were investigated. Characterization techniques, including Brunauer-Emmett-Teller (BET) surface area analysis, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), and X-ray diffraction (XRD) were employed to analyze the catalysts' properties. Results showed that increasing Ni loading to 10 wt.% improves the catalytic properties. However, by increasing the Ni loading, a decrease in catalytic properties due to increasing particle size, creating NiO bulk phase and surface pore blockage is obvious. A series of experiments were performed to investigate the effect of steam usage on catalytic properties. TPO analysis revealed that steam addition reduces the carbon deposition and shifts oxidation peaks to lower temperatures; consequently, the activity and stability of the catalyst will be enhanced. Although the 5 - 7.5 vol.% of steam in the feed composition significantly stabilizes the catalyst, it is possible to produce H2-rich synthesis gas, and conversely, increasing the temperature reduces the H2/CO ratio. Various examinations were conducted under different conditions, including varying gas hourly space velocity (GHSV), carbon-to-glycerol ratio (CGR), and temperature, to obtain more comprehensive data on the catalysts.

Promotional effects of Nb2O5 on ceria doped Ni catalysts for selective hydrogenation of 1,3-butadiene to butenes: Combined experimental and DFT approach

Developing low cost, active and selective catalysts that would replace the more deployed noble metals is desirable for hydrogenation of 1,3-butadiene. Herein, we prepared Ni catalysts supported on niobium-cerium oxides and characterization was carried out with TGA, XRD, H2-TPR, H2-TPD, HR-TEM, XPS, FTIR, N2 adsorption–desorption, and EDS mapping. Density functional theory (DFT) computes the reaction energies controlling the 1,3-butadiene hydrogenation. H2-TPR revealed that the inclusion of niobium oxide in the catalysts confer stronger metal support interaction that promotes the surface and bulk reduction of cerium oxide and leads to the improvement in the formation of surface Ce3+ as confirmed from the XPS analysis. 1,3-butadiene conversion was tested between 100 °C-350 °C and the catalysts exhibit high conversion at lower Ni loading. We found that the niobium inclusion directed the selectivity towards near complete butene formation even at higher temperature. The onset of decline in activity was observed at temperatures above 250 °C with the simultaneous formation of propene and propane and the disappearance of butane. Guided by the reaction results and the temperature programmed oxidation analysis (TPO), we proposed the reaction mechanism leading to the deactivation, and this entails butane decomposition to propene and surface carbene, while propane is formed from propene, the surface carbene occasioned in the formation of harmful carbon as evident from TPO results. Carbonaceous species formed on the catalysts were minimized on the niobium containing catalysts.

Dysprosium promotion on Co/Al2O3 catalysts towards enhanced hydrogen generation from methane dry reforming

Dysprosium (Dy) promoted Co/Al2O3 catalysts with different Dy loadings (0-3 wt%) were synthesized via an impregnation approach for methane dry reforming. Promoter addition enhanced the basicity of catalysts owing to the basic attribute of Dy2O3. Co3O4 crystallite sizes were reduced from 8.15 to 6.68 nm with 0.1–0.3 wt%Dy promotion due to the diluting effect, resulting in higher metal dispersion. Particularly, at 973 K, 0.3 wt%Dy appeared as the best promoter loading and achieved the highest CH4 conversion, as well as H2 and CO yields of the corresponding 79.4%, 65.8% and 89.2% because of growing basic site density and the enhancing number of Co active sites. The temperature-programmed oxidation analyses also revealed that 0.3%Dy-10%Co/Al2O3 suppressed carbonaceous deposition from 12.84% to 7.76% since the extra oxygen mobility and redox cycling of Dy2O3 could effectively oxidize surface carbonaceous species to CO and H2.

Boosting Thermal Stability of Volatile Os Catalysts by Downsizing to Atomically Dispersed Species.

Os-based catalysts present remarkable catalytic activity; however, their use has been limited by the undesirable side reactions that generate highly toxic and volatile OsO4 even at room temperature. Herein, we demonstrate that the thermal stability of Os-based catalysts can be dramatically improved by downsizing Os nanoparticles (NPs) into atomically dispersed species. We observed that Os NPs were converted into OsO4 after calcination at 250 °C followed by sublimation, whereas single Os sites retained their structure after calcination. Temperature-programmed oxidation analysis confirmed that Os NPs started to undergo oxidation at 130 °C, whereas atomically dispersed Os preserved its state up to 300 °C. The CO oxidation activity of the atomically dispersed Os catalyst at 400 °C (100% conversion) was stably preserved over 30 h. By contrast, the activity of Os NP catalyst declined drastically. This study highlights the unique catalytic behavior of atomically dispersed catalysts, which is distinct from that of NP-based catalysts.

Influence of Global Operating Parameters on the Reactivity of Soot Particles from Direct Injection Gasoline Engines

The aim of this study is to investigate the impact of global operating parameters, e.g., engine speed, brake mean effective pressure, and air–fuel ratio, of a turbocharged 4-cylinder GDI engine on the reactivity of soot particles against oxidation. The knowledge of soot reactivity is crucial for optimizing gasoline particulate filter regeneration strategies and is, consequently, a key parameter for reducing fuel consumption and CO2 emissions. In this work, time-resolved in-cylinder soot concentrations and exhaust particle size distributions are measured by using two-color pyrometry, engine exhaust particle sizer and smoke meter, respectively. Reactivity against oxidation by molecular oxygen is determined by temperature programmed oxidation analysis. To derive a physicochemical explanation for varying soot reactivity, the morphological and nanostructural primary particle structure of collected samples is analyzed using high-resolution electron microscopy and image analysis algorithms. The results reveal that engine operating parameters affect soot reactivity differently. While engine speed has only a slight effect, a reduction of air/fuel ratio (λ < 1.0) or an increase of BMEP > 10 bar significantly reduces the soot oxidation reactivity. These findings give evidence, that the quality of the fuel/air mixture is a significant parameter influencing soot reactivity. Measured soot concentrations substantiate the hypothesis that low-sooty homogeneous premixed combustion of a homogeneous fuel/air mixture favors formation of high-reactive soot particle fractions. Reactive soot particle aggregates are composed of multiple soot fractions of different reactivity. Reactive primary particles are composed of short graphene-like layers and vice versa, providing a physicochemical explanation for varying soot reactivity depending on engine operating conditions.

A key role of soft and refractory coke in the deactivation of γ–Al2O3 catalysts during low-temperature methyl oleate epoxidation: An experiment and DFT study

This work studies the deactivation of the γ-Al2O3 catalyst in a low-temperature methyl oleate epoxidation reaction. The performance at each cycle of spent catalyst correlated to the formation of soft and refractory coke on the catalyst was probed by the temperature-programmed oxidation analysis and FT-IR. As a result, soft coke contributed as the major coke species, including an ester functional group. Furthermore, the coke adsorption on the surface and the electron transfer was analyzed by density functional theory-based calculation. It was found that the strongly adsorbed refractory coke on the catalyst is prone to adsorb on the main Al active site blocking the formation of the Al–OOH site. This phenomenon is responsible for the main reaction in contrast to the soft coke that prefers the other Al sites. Thus, controlling the refractory coke formation is crucial to control the overall catalyst performance, although present in a small amount.

Evaluating the drop of electrochemical performance of Ni/YSZ and Ni/ScSZ solid oxide fuel cells operated with dry biogas

SummaryThis work is aimed at evaluating the influence of carbon deposition on the power density drop of in‐house fabricated Ni/YSZ and Ni/ScSZ solid oxide fuel cells (SOFCs) operating in dry internal reforming of simulated biogas (CH4/CO2 = 2). An immediate drop of open‐circuit voltage (OCV) and maximum power densities is observed when the fuel changes from hydrogen to biogas, 86.5% and 33.3% for the Ni/YSZ and Ni/ScSZ cells, respectively with mass transfer polarisation dominates Ni/YSZ polarisation. Carbon deposition is investigated as the cause of the reduction in performance by quantification of deposited carbon by temperature programmed oxidation (TPO) and catalytic activity test. Results from TPO analysis show unexpectedly higher amount of carbon on the Ni/ScSZ cells (2.35 × 10−3 mgC/mgcat) as compared to Ni/YSZ (5.68 × 10−4 mgC/mgcat) despite higher performance of the former. Catalytic activity tests reveal a low carbon oxidation rate compared to an initially higher methane decomposition reaction, leading to carbon deposition in both cells, in which the methane decomposition reaction of Ni/ScSZ is higher. Different effects are observed on the pellets, where the carbon deposited on Ni/YSZ deactivates the reforming reaction sites as quick as 20 minutes into the operation, whereas carbon deposited on the Ni/ScSZ pellet did not show the same blocking effect on the catalyst due to the different carbon morphology formed. A graphitic whisker‐like rod structure is observed on Ni/ScSZ while amorphous non‐crystalline carbon covers the Ni/YSZ pellets with 3 hours exposure to high methane content dry biogas (CH4/CO2 = 2). The difference of carbon structure affects the amount of carbon quantified in the TPO analysis where most of the amorphous carbon oxidises while some of the graphitic carbon deposits remain.

Optimization of Nickel-Based Catalyst Composition and Reaction Conditions for the Prevention of Carbon Deposition in Toluene Reforming

In this study, nickel-based reforming catalysts were synthesized for the reforming of toluene, a major component of thinners and widely used as an organic solvent. The reaction characteristics of these catalysts were investigated by both steam reforming and auto-thermal reforming. Reforming aromatic hydrocarbons like toluene to produce synthesis gas is difficult because carbon deposition also occurs, and the deposition of carbon lowers the activity of the catalyst and causes a pressure drop during the reaction process. In order to maintain a stable reforming process, a catalytic reaction technique capable of suppressing carbon deposition is required. Steam reforming and auto-thermal reforming of toluene were used in this study, and the temperature of the catalyst bed was remarkably reduced, due to a strong endothermic reaction during the reforming process. By using scanning electric microscopy (SEM), X-ray diffraction (XRD), and temperature-programmed oxidation analysis, it is shown that carbon deposition was markedly generated due to a catalyst bed temperature decrease. In this study, optimum conditions for catalyst composition and the reforming reaction are proposed to suppress the formation of carbon on the catalyst surface, and to remove the generated carbon from the process. In addition, ceria and zirconia were added as catalytic promoters to inhibit carbon deposition on the catalyst surface, and the carbon deposition phenomena according to the catalyst’s promoter content were investigated. The results showed that the carbon deposition inhibition function of CeO2, via its redox properties, is insignificant in steam reforming, but is notably effective in the auto-thermal reforming of toluene.

Graphene and carbon nanotubes by CH4 decomposition over Co Al catalysts

Abstract Catalysts containing Co and Al were prepared to obtain graphene and carbon nanotubes (CNTs) via the catalytic decomposition of CH4. The catalysts were prepared by co-precipitation with molar percentages of Co between 50 and 100%. The effects on the formed carbon of the catalyst composition, reaction temperatures of 500–900 °C, and activation with hydrogen were evaluated. The carbon that formed during the reactions was analyzed using Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and temperature-programmed oxidation (TPO). The Raman spectra of the samples containing Al were characteristic of CNTs, with the IG/ID ratio increasing as the Co/Al ratio and reaction temperature increased. The Co100 sample presented a Raman spectrum indicative of few-layer graphene. The TPO analysis revealed cobalt carbide oxidation for the Co100 sample, and this phase was related to the formation of graphene. CNTs were favored by Co Al mixed oxides and reaction temperatures of 500–700 °C. Graphene was favored by the Co3O4 phase and higher reaction temperatures.

Dry reforming of methane for syngas production over Ni\u2013Co-supported Al2O3\u2013MgO catalysts

This research project focuses on the development of catalysts for syngas production by synthesizing Ni–Co bimetallic catalyst using aluminum oxide (Al2O3) and magnesium oxide (MgO) as the catalyst support. Ni/Al2O3 (CAT-1), Ni–Co/Al2O3 (CAT-2) and Ni–Co/Al2O3–MgO (CAT-3) nanocatalysts were synthesized by sol–gel method with citric acid as the gelling agent, and used in the dry reforming of methane (DRM). The objective of this study is to investigate the effects of Al2O3 and MgO addition on the catalytic properties and the reaction performance of synthesized catalysts in the DRM reactions. The characteristics of the catalyst are studied using field emission scanning electron microscope (FESEM), Brunauer–Emmett–Teller (BET), X-ray powder diffraction (XRD), transmission electron microscopy, H2-temperature programmed reduction, CO2-temperature programmed desorption and temperature programmed oxidation analysis. The characteristics of the catalyst are dependent on the type of support, which influences the catalytic performances. FESEM analysis showed that CAT-3 has irregular shape morphology, and is well dispersed onto the catalyst support. BET results demonstrate high surface area of the synthesized catalyst due to high calcination temperature during catalysts preparation. Moreover, the formation of MgAl2O4 spinel-type solution in CAT-3 is proved by XRD analysis due to the interaction between alumina lattice and magnesium metal which has high resistance to coke formation, leading to stronger metal surface interaction within the catalyst. The CO2 methane dry reforming is executed in the tubular furnace reactor at 1073.15 K, 1 atm and CH4/CO2 ratio of unity to investigate the effect of the mentioned catalysts. Ni–Co/Al2O3–MgO gave the highest catalyst performance compared to the other synthesized catalysts owning to the strong metal–support interaction, high stability and significant resistance to carbon deposition during the DRM reaction.

Electrochemical promotion for hydrogen production via ethanol steam reforming reaction

In this work we have investigated for the first time the electrochemical activation of a catalyst for the ethanol reforming reaction. For that purpose, a Pt-KβAl2O3 electrochemical catalyst has been prepared, characterized and tested under ethanol reforming reaction conditions. The electrochemically supply of potassium ions under negative polarization step, strongly increased the hydrogen production rates leading to a reversible and controllable promotional effect. It has been attributed to the enhancement of the kinetic of ethanol dehydrogenation reaction, due to the strengthening of the chemisorptive bond of intermediate ethoxy molecules. It will increase the stability of this intermediate, thus favoring its formation, which initiates the ethanol reforming process. However, a large amount of carbonaceous species were formed on the catalyst surface during the negative polarization step that causes a continuous decrease in the catalytic activity under long polarization times. Under these conditions, the application of a catalyst potential of 2 V leads to a complete removal of the previous deposited carbonaceous molecules which allows further electrochemical activation steps. The obtained catalytic results have been supported by in-situ temperature programmed oxidation analysis and ex-situ Raman spectroscopy and Scanning Electron Microscopy. These techniques, in conjunction with the obtained catalytic results, have demonstrated the interest of the EPOC phenomenon for in-situ tuning the adsorption of reactants molecules on catalyst surface and its application in the hydrogen production technology, improving catalyst conversion and selectivity.

Catalytic characteristics of pyrolysis volatile matter from biomass/biomass components on a novel Ni-based catalyst supported by iron slag

In this study, a novel Ni-based catalyst supported by iron slag (IS) was used to catalyze the pyrolysis volatile matter of pine sawdust, and the catalytic characters of the novel catalyst were compared with those of alumina Ni-based catalysts. In addition, the catalytic performances of the novel iron slag Ni-based catalyst on pyrolysis volatile matter of biomass components (lignin, cellulose, and hemicellulose) were experimentally investigated. Experimental results showed that the iron slag Ni-based catalyst could remove more than 90% of tar, which was close to the catalytic performance of common alumina nickel catalysts. The temperature-programmed oxidation analysis results showed that the coke amount was less than 0.6% of IS Ni-based catalyst, indicating the superior performance to alumina nickel catalyst. The analysis results of the catalytic effect on biomass components volatile matter showed that the IS Ni-based catalyst could significantly improve the tar conversion of lignin (92.71%). We compared the dew points of various biomass components and found that lignin was the main influencing factor of the dew point of pyrolysis tar. The catalytic performance of the IS Ni-based catalyst verified the economic value and environmental effect of IS for its reutilization. We analyzed the catalytic effect of pyrolysis volatile matter of biomass components on the novel catalyst for the purpose of selecting proper biomass materials.

Hydrogen production by steam reforming of ethanol over Ni/Al2O3-La2O3 xerogel catalysts

A series of nickel catalysts supported on binary Al2O3-La2O3 xerogel supports with different La/Al molar ratio were prepared via a sol-gel method and a subsequent wetness impregnation method for use in the ethanol steam reforming reaction. The effect of La/Al molar ratio on the characteristics and catalytic activities of Ni/Al2O3-La2O3 catalysts in the hydrogen production by steam reforming of ethanol was investigated. The prepared Ni/Al2O3-La2O3 catalysts were characterized by nitrogen adsorption-desorption, ICP-AES (inductively coupled plasma atomic emission spectroscopy), XRD (X-ray diffraction), 27Al MAS NMR (magicangle spinning nuclear magnetic resonance), TPR (temperature-programmed reduction), TPO (temperature-programmed oxidation), TEM (transmission electron microscopy), and TPD (temperature-programmed desorption) analyses. Physicochemical properties of the catalysts were suppressed with increasing La/Al molar ratio because of the formation of defective structure within the alumina lattice. Acidity of Ni/Al2O3-La2O3 catalysts was weakened with increasing La/Al molar ratio, while basicity of the catalysts was strengthened. Nickel dispersion and nickel surface area increased with increasing La/Al molar ratio. On the contrary, ethanol adsorption capacity of the catalysts decreased with increasing La/Al molar ratio due to their unfavorable physicochemical properties. Hydrogen yield showed a volcano-shaped curve with respect to La/Al molar ratio, where an optimal amount of La content was required to achieve the most promising catalytic performance. The enhanced catalytic activity at an intermediate La/Al molar ratio is believed to be due to the offset of two opposite trends between nickel surface area and ethanol adsorption capacity of Ni/Al2O3-La2O3 catalysts.

Regenerability of the CuO–ZnO–MnO/SAPO-18 catalyst used in the synthesis of dimethyl ether in a single step

The study has focused on the regenerability of the CuO–ZnO–MnO/SAPO-18 (CZMn/S) bifunctional catalyst used in the direct synthesis of dimethyl ether (STD process) from H2 + CO + CO2 feeds. The runs have been conducted in a fixed bed reactor under the following conditions: 250–300 °C; 10–40 bar; 1.25–10.18 gcat h molC−1; time on stream, 5–30 h; CO2/CO molar ratio, 0–1; feeding H2 + CO + CO2 with a H2/COx molar ratio of 3. Coke deposition has been determined as the main deactivation cause, and both the measurement of the coke content and the identification of three types of coke have been carried out by means of temperature programmed oxidation analyses. Reaction-regeneration cycle runs have been carried out in a fixed bed isothermal reactor, concluding that it is possible to regenerate the bifunctional catalyst by the combustion of coke with air, at 300 °C (48 h). Under these conditions, the catalyst undergoes a slight Cu sintering in the first reaction-regeneration cycle but recovers completely the remaining activity in the successive cycles.

Improving Plasma Regeneration Conditions of Pt–Sn/Al2O3 in Naphtha Catalytic Reforming Process Using Atmospheric DBD Plasma System

The catalytic naphtha reforming is one of the largest processes of petroleum industry that is used to rebuild the low-octane hydrocarbons in the naphtha to more valuable high-octane gasoline called reformate without changing the boiling point range. An atmospheric pressure pin to plate dielectric barrier discharge (DBD) plasma was used to remove carbonaceous contaminant from the coked Pt–Sn/Al2O3 catalysts during the naphtha reforming process. The effects of treatment time and flow ratios of O2/Ar and O2/He on the carbon content of the coked catalysts were investigated. The produced radicals and active species of the plasma process were identified by optical emission spectroscopy. To confirm removing the coke from the catalyst, thermal gravimetric/differential thermal analysis and temperature programmed oxidation analysis were done. Effects of treatment time and flow ratios of O2/Ar and O2/He on the carbon content of the coked catalysts were investigated by applying elemental analysis. The results of X-ray diffraction, X-ray fluorescence, Brunauer–Emmett–Teller, and CO adsorption showed that the structure and specifications of regenerated catalysts remained without significant changes during the plasma treating. The catalyst performance test revealed that DBD plasma regenerated catalysts increased the aromatic content of the feed as well as the fresh catalysts. The results showed that the plasma treatment method for regeneration of Pt–Sn/Al2O3 can be applied at lower temperature and pressure relative to the thermal regeneration method.

Syngas production from CO2 reforming of methane over ceria supported cobalt catalyst: Effects of reactants partial pressure

The production of syngas from CO2 (dry) reforming of methane is an environmental friendly process since it contributed to the mitigation of CH4 and CO2, the two principal components of greenhouse gases. In this study, ceria-supported cobalt catalyst was synthesized using wet-impregnation method and tested for the production of syngas from methane dry reforming. The main objective of this study is to investigate the effects of partial pressures of the reactants (CH4 and CO2) on the performance of the ceria-supported cobalt catalyst for syngas production via methane dry reforming. The CH4 and CO2 partial pressures were investigated within the range of 5–50 kPa at reaction temperatures of 923–1023 K in a fixed bed reactor at atmospheric pressure and gas hourly velocity of 30,000h−1. The highest conversion of CH4 and CO2 were obtained to be 78 and 80% at CH4 partial pressure of 45 and 25 kPa respectively. Syngas ratio of 1.0 was produced at CH4 partial pressure of 40 kPa (reaction temperature of 1023 K). The maximum yield of 40% and 38% were obtained for H2 and CO, respectively. The used catalyst was characterized by temperature programmed oxidation (TPO) for possible carbon deposition. The TPO analysis revealed the formation of graphitic carbon. The findings from this study show that syngas production from methane dry reforming over ceria-supported cobalt catalyst is significantly influenced by the variation in the partial pressure of the reactants.

Asphaltene Adsorption onto Acidic/Basic Metal Oxide Nanoparticles toward in Situ Upgrading of Reservoir Oils by Nanotechnology

The effects of surface acidity and basicity of metal oxide nanoparticles on the thermodynamics of asphaltene adsorption were studied. Three different categories of metal oxides/salts with acidic (WO3 and NiO), amphoteric (Fe2O3 and ZrO2), and basic (MgO and CaCO3) surfaces were synthesized, and their textural, structural, and acid-base properties were characterized. Asphaltenes were extracted from a dead oil sample and characterized by X-ray powder diffraction and Fourier transform infrared spectroscopy. The acid and base numbers of the asphaltenes were measured. The nanoparticles were added to the asphaltene-toluene solutions, and the amount of adsorbed asphaltene was obtained through centrifugation followed by UV-vis spectroscopy of the supernatant liquid and temperature-programmed oxidation analysis of the precipitated solid. The concentrations of organic acid and base groups in the asphaltenes are 2.75 and 12.34 mg of KOH/g, respectively, indicating that the asphaltenes are more basic in nature. Isotherms of the asphaltene adsorption onto the six metal oxides/salts fit the Langmuir model closely. The asphaltene adsorption capacity of the nanoparticles is 1.23-3.67 mg/m(2) and decreases in the order of NiO > Fe2O3 > WO3 > MgO > CaCO3 > ZrO2, concomitant with the synergetic effects of acidity and the net charge of the surfaces. High-resolution transmission electron microscopy illustrates that the asphaltenes are spread out over the surfaces with no short-range/long-range order. The adsorption of the asphaltenes onto the six samples is exothermic and spontaneous with the Gibbs energy change of -27.80 to -28.79 kJ/mol at 25 °C. The absolute value of the enthalpy change of the adsorption is calculated to be within the range of 5-20 kJ/mol. Acid-base interaction and electrostatic attraction seem to be the dominant forces contributing to the adsorption of the asphaltenes onto the metal oxide/salt surfaces.

Quantitative determination of carbon in titania photocatalysts by temperature programmed oxidation method

This study was directed to the optimization of a reliable and innovative approach, for the qualitative and quantitative analysis of carbon-doped titania photocatalysts. In particular, we report an easy procedure, based on the Temperature Programmed Oxidation (TPO) method for the determination and prediction of the carbon amount on the final catalysts. The synthesized Ti(OH)4 photocatalysts were doped with different amount of succinic acid and an in-depth characterization was carried out by X-ray diffraction (XRD), physisorption of gas, elemental analysis, and temperature programmed oxidation (TPO). The final amounts of C, after calcinations, were determinate by TPO analysis through the setting up of a calibration curve.

Evaluation of Biochars by Temperature Programmed Oxidation/Mass Spectrometry

Biochars produced from thermochemical conversions of biomass were evaluated by temperature programmed oxidation (TPO). This technique, used to characterize carbon deposits on petroleum cracking catalysts, provides information on the oxidative stability of carbonaceous solids, where higher temperature reactivity indicates greater structural order, an important property for biochar applications. Differences between TPO profiles of biochars generated by fast pyrolysis of soy straw, barley straw, switchgrass, bamboo, and various woods demonstrated that the oxidative stabilities of the biochars are dependent on the starting biomass. Biochars from softwood and hardwood feedstocks were also processed by torrefaction and gasification to assess the impact of the thermoprocessing method on the TPO data. Results from these TPO analyses showed that the biochars produced under higher temperature conditions afford biochars that are more oxidation resistant. Biochars produced from pine wood (softwood) were consistently more resistant to oxidation compared to their hardwood counterparts. This exploratory study represents the first application of TPO to biochars.

Catalytic Steam Gasification of Biomass for a Sustainable Hydrogen Future: Influence of Catalyst Composition

Hydrogen is regarded as a clean energy for fuelling the future. Hydrogen will be the energy carrier from other resources such as hydropower, wind, solar and biomass. Producing hydrogen from gasification of biomass wastes, particularly in the presence of steam, represents a promising route to produce this clean and CO2-neutral fuel. The steam pyrolysis–gasification of biomass (wood sawdust) was carried out with various nickel-based catalysts for hydrogen production in a two-stage fixed bed reaction system. The wood sawdust was pyrolysed in the first reactor and the derived products were gasified in the second reactor in the presence of the catalyst and steam. The synthesised Ni–Ca–Al and Ni–Zn–Al catalysts were prepared by co-precipitation method with different Ni loadings of 20 mol% and various Zn/Al or Ca/Al ratios, which were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). The results showed that the Ni/Zn–Al (1:9) catalyst resulted in higher hydrogen production (23.9 mmol H2 g−1 biomass) compared with the Ni/Ca–Al (1:9) catalyst (12.7 23.9 mmol H2 g−1 biomass) and in addition, the increase of Ca or Zn content in the catalyst slightly increased the hydrogen production. The TPO results showed that the catalyst suffered negligible coke deposition from the catalytic steam pyrolysis/gasification of wood sawdust. Additionally, Na2CO3 basic solution was also found to produce a catalyst with better performance and lower coke deposition, compared with NH4OH catalyst preparation agent, as observed by TPO, SEM and TEM analysis.