Ni Loading Research Articles

Tuning CO2 to CO Conversion on Metal-Doped Carbon Catalysts

One of the significant challenges faced during electrochemical CO2 reduction (ECO2RR) is the low selectivity of the products obtained. The best example is polycrystalline Cu, which can electrochemically produce hydrocarbons and alcohols but with poor selectivity.1, 2 To date, high selectivity has been achieved only towards CO and formate on Au and Sn surface, respectively but scalability and commercialization are limited owing to their cost and stability. Metal-nitrogen-carbon (MNC) materials are comparable to Au or Ag catalysts, albeit with their lower overpotentials, higher mass activity and high selectivity toward CO.3 , 4 During the pyrolysis of N-containing carbon molecules, different chemical functionalities such as pyridinic, pyrrolic and graphitic N atoms can be formed, each behaving as a product-specific active site. 5 It is still debatable whether pyrdinic or pyrrolic N is responsible for CO2RR activity; thus, it remains unclear how to favor CO2 reduction over hydrogen evolution.In this work, we aimed to synthesize C2N-like covalent organic frameworks, with 8-10 Å pore size, tailored to host dual atoms coordinated to nitrogen. Such sites are expected to favor C-C coupling and produce multi-carbon products during ECO2RR. A step-by-step synthetic approach was employed to optimize the CO2RR:HER ratio through: Tuning carbon:nitrogen ratio using two different synthetic approaches.Reducing nitrogen in the carbon matrix through pyrolyzing at different temperatures (700, 800 and 900 oC),Doping phosphorus and nitrogen into the carbon matrixTuning CO2RR product distribution through different metals (Fe and Ni) doping. EXAFS and STEM studies revealed the presence of a mixture of single and dual atomic sites. XPS and ICP results showed that Fe and Ni loadings <2 wt% could be obtained in the C2N materials. Higher hydrogen evolution, owing to the higher N-content, was observed at a lower pyrolysis temperature which decreased at a pyrolysis temperature of 900 oC. Both Fe-NC and Ni-NC selectively produced CO, thus suppressing FE H2 to <5%. Fe-NC also exhibited lower overpotential for CO production compared to its Ni-NC counterpart. A small percentage of ethanol and 2-propanol (FE<5%) was observed indicating the favoured C-C coupling on the dual-atomic sites. Further optimization of the metal-N coordination environment may allow for an improved selectivity for >C2 products. References K. P. Kuhl, E. R. Cave, D. N. Abram and T. F. Jaramillo, Energy Environ. Sci., 5, 7050 (2012). S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramillo and I. Chorkendorff, Chem. Rev., 119, 7610 (2019). A. S. Varela, N. Ranjbar Sahraie, J. Steinberg, W. Ju, H.-S. Oh and P. Strasser, Angew. Chem. Int. Edit., 54, 10758 (2015). A. S. Varela, W. Ju, A. Bagger, P. Franco, J. Rossmeisl and P. Strasser, ACS Catal., 9, 7270 (2019). Y. Lum and J. W. Ager, Nat. Catal., 2, 86 (2019).

Carbon Dioxide Reforming of Methane over Nickel-Supported Zeolites: A Screening Study

As the utilization of zeolites has become more frequent in the dry reforming of methane (DRM) reaction, more systematic studies are required to evaluate properly the influence of zeolites’ composition and framework type on the performance. Therefore, in this work, a step-by-step study was performed with the aim of analyzing the effects of Ni loading (5, 10 or 15 wt.% over USY(3) zeolite), Si/Al ratio (3, 15 or 38 on USY zeolites with 15 wt.% Ni) and framework type (USY, BEA, ZSM-5 or MOR for 15 wt.% Ni and Si/Al ratios of ≈40) on catalysts’ properties and performances. Increasing Ni loadings enhanced CH4 and CO2 conversions even though the catalysts’ stability was decreasing over the time. The variation of the Si/Al ratio on USY and the use of different zeolites had also a remarkable impact on the catalytic performance. For instance, at 500–600 °C reaction temperatures, the catalysts with higher basicity and reducibility exhibited the best results. However, when the temperature was further increased, catalysts presenting stronger metal–support interactions (nickel nanoparticles located in mesoporous cavities) displayed the highest conversions and stability over time. In brief, the use of 15 wt.% Ni and a USY zeolite, with both micro- and mesopores and high surface area, led to the best performances, mainly attributed to a favorable number of Ni0 active sites and the establishment of stronger metal–support interactions (due to nanoparticles confinement inside the mesopores).

Biocrude production by catalytic hydrothermal liquefaction of wood chips using NiMo series catalysts

In this work, hydrothermal liquefaction of wood chips was studied for biocrude production using a mix of Ni–Mo nitrides and carbides. The catalytic materials were synthesized by a temperature-programmed reaction method at 800 °C under a hydrogen atmosphere with nickel loads from 0 to 20 wt%. Lignin contained in the lignocellulosic biomass was successfully release via Kraft process. Hydrothermal liquefaction was carried out in a batch reactor at 320 °C with an initial pressure of 1000 psi of H2. According to characterization results, nanostructured catalysts with a mix of Ni2Mo3N/Mo2C compo4unds were obtained. NiMo series catalysts composition varies with nickel loads. The catalytic activity shows a reduction in the amount of solid products and an increase in the production of gaseous products as a function of the increase Ni loadings on the catalyst. The most optimal production of biocrude was obtained with the NiMo-10 catalyst, since 81.43% of the total product corresponded to water soluble products (WPS) fraction and the oil fraction, while the solids fraction represented the 6.43% of the total product. Hydrothermal liquefaction catalytic processes were selective towards WSP fraction, improving biocrude quality and favoring biocrude conversion into advanced biofuels.

Synergistic effect of Zn with Ni on ZSM-5 as propane aromatization catalyst: effect of temperature and feed flowrate

This work shows how propane was catalytically converted to aromatic compounds over Zn-Ni/HZSM-5 to investigate the synergistic role of nickel as a zinc stabilizer and promoter in propane aromatization. Co-impregnation method was employed for Zn-Ni/ZSM-5 synthesis fixed 2 wt% of zinc and 1, 2 and 3 wt% of nickel. Modified catalysts’ were fully characterized. Catalysts crystallinity, structure and microporosity were retained from the analysis results. The propane aromatization process was conducted at 540 °C, 1200 ml/g-h gas hourly space velocity and atmospheric pressure. The presence of Ni with Zn improved catalytic performance for all Ni loading. Aromatic selectivity and propane conversion were improved, with the best performance to be Zn-Ni/ZSM-5 with 2 wt% Zn, 2 wt% Ni on ZSM-5 averaging 88 and 60% for twelve hours’ time on stream. Aromatic selectivity on Zn-Ni/ZSM-5 is eight times better than the parent HZSM-5 and one and half times better than the Zn/ZSM-5 catalyst. The electronic interaction of zinc and nickel resulting from equality of oxidation state of +1 and +2 and metal-binding energy change synergistically improved the catalytic performance of the bimetallic Zn-Ni/ZSM-5 over the HZSM-5 and Zn/ZSM-5. Flowrate increase from 6 to 35 ml min−1 decreased propane conversion from 80–40% with increased aromatic selectivity from 55–80%. Temperature increase from 500–580 °C favours both propane conversion and aromatic selectivity increase from 50–68 and 55–92% respectively. The metallic interactions from H2-TPR and XPS analysis revealed a big improvement in propane conversion, aromatic selectivity and product distribution.

Dry Reforming of Methane on Ni/Nanorod-CeO2 Catalysts Prepared by One-Pot Hydrothermal Synthesis: The Effect of Ni Content on Structure, Activity, and Stability

The nanorod morphology of the CeO2 support has been recognized as more beneficial than other morphologies for catalytic activity in the dry reforming of methane. Ni/nanorod-CeO2 catalysts with different Ni contents were prepared by one-pot hydrothermal synthesis. Samples were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), H2-temperature-programmed desorption (H2-TPD), field emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS), Brunauer–Emmet–Teller (BET) and Barrett–Joyner–Halenda (BHJ) analysis. The effect of Ni content on the size and the intrinsic strain of ceria was analyzed by the Size–Strain plot and Williamson–Hall plot of XRD data. The average Ni particle size and Ni dispersion were determined by H2-TPD. XRD and H2-TPR analysis revealed a strong Ni–support interaction that limited nickel sintering. The activity for the dry reforming of methane was tested with the stoichiometric mixture CO2:CH4:N2:He = 20:20:20:140, gas hourly space velocity (GHSV) = 300 L g−1 h−1, and temperatures in the range of 545–800 °C. The turnover frequency (TOF) value increased linearly with the average Ni particle size in the range of 5.5–33 nm, suggesting the structure sensitivity of the reaction. Samples with Ni loading of 4–12 wt.% showed high H2/CO selectivity and stability over time on stream, whereas the sample with a Ni loading of 2 wt.% was less selective and underwent rapid deactivation. Only a small amount of nanotubular carbon was observed by FE-SEM after the time-on-stream experiment. Deactivation of the low-Ni-content sample is ascribed to the easier oxidation of the small Ni particles.

One-step synthesis of highly active and stable Ni-ZrO2 catalysts for the conversion of methyl laurate to alkanes

A series of Ni-ZrO2 catalysts with different Ni loading were prepared and evaluated for methyl laurate conversion. Characterizations show that the 10Ni-ZrO2 bears the smallest Ni crystal size; the highest atomic content of surface Ni0, surface oxygen vacancy and Ni-O-Zr interfaces; then exhibits the highest activity and stability towards methyl laurate conversion with nearly 100% yield of alkanes and 87.6% selectivity to undecane at 280 °C, 2 MPa H2. The t-ZrO2(112) lattice plane can motivate the deoxygenation while the t-ZrO2(002) promotes cracking reactions, resulting in low selectivity to undecane. Moreover, 10Ni-ZrO2 performs wide applicability for transforming crude oils into alkanes.

Enhancing oxidative hydration of ethylene towards ethylene glycol over metal-modified titanosilicate catalysts

Metal-dopant modification is a promising approach to enhance the catalytic performance of titanium silicate molecular sieve. Herein, titanium silicalite-1 (TS-1) with different titanium contents and a series of metal-doping modified TS-1 are prepared, to enhance the synthesis of ethylene glycol (EG) through oxidative hydration of ethylene. The EG selectivity show a volcano relationship along with the increase of Ni addition, and reach maximum in 80.63 % at 0.13 wt % Ni loading. The Ni promoter mechanism is revealed that NiO species enhances the electropositivity of skeleton Ti and neutralizes the surface acidity of TS-1, which improves the efficient utilization of H2O2 and selectivity of EG. Furthermore, Ni-modified TS-1 shows superior stability to TS-1, as well as satisfactory reusability since the deactivation of catalyst is reversible through high-temperature calcination. This work demonstrates the feasibility and mechanism of Ni promoter and provides a promising strategy for the development of TS-1 catalysts.

Tuning Particle Sizes and Active Sites of Ni/CeO2 Catalysts and Their Influence on Maleic Anhydride Hydrogenation.

Supported metal catalysts are widely used in industrial processes, and the particle size of the active metal plays a key role in determining the catalytic activity. Herein, CeO2-supported Ni catalysts with different Ni loading and particle size were prepared by the impregnation method, and the hydrogenation performance of maleic anhydride (MA) over the Ni/CeO2 catalysts was investigated deeply. It was found that changes in Ni loading causes changes in metal particle size and active sites, which significantly affected the conversion and selectivity of MAH reaction. The conversion of MA reached the maximum at about 17.5 Ni loading compared with other contents of Ni loading because of its proper particle size and active sites. In addition, the effects of Ni grain size, surface oxygen vacancy, and Ni–CeO2 interaction on MAH were investigated in detail, and the possible mechanism for MAH over Ni/CeO2 catalysts was deduced. This work greatly deepens the fundamental understanding of Ni loading and size regimes over Ni/CeO2 catalysts for the hydrogenation of MA and provides a theoretical and experimental basis for the preparation of high-activity catalysts for MAH.

Effect of Fe and La on the Performance of NiMgAl HT-Derived Catalysts in the Methanation of CO2 and Biogas

Bulk Ni-based catalysts derived from hydrotalcite-type (HT) compounds show enhanced stability in the hydrogenation of CO2 into CH4, in comparison to their supported counterparts. The composition of the parent hydrotalcite determines the Ni loading and particle size, as well as the basicity of the catalysts. In this work, a comparison between the effect of Fe and La on the performance of NiMgAl HT compounds (Ni/Mg/Al = 25/50/25 atomic ratio) calcined at 600 °C is investigated. After a reduction pretreatment at 750 °C, both promoters enhance the activity in the low-temperature range; however, the La-containing catalyst reaches a better CH4 productivity rate at high oven temperature (i.e., 200 L gNi–1 h–1 at 325 °C). Although the formation of the NiFe alloy improves the activity, lanthanum keeps smaller Ni0 particles and provides a higher basicity to the mixed oxide than Fe. The activity of the NiMgLaAl catalyst can be further tailored by increasing the Ni loading from 25.6 wt % (Ni25Mg50La5Al20) to 44.6 wt % (Ni50Mg25La5Al20). Lastly, the feasibility of HT-derived catalysts in the direct methanation of clean biogas is proved.

Connecting cation site location to alkane dehydrogenation activity in Ni/BEA catalysts

Ni-modified beta zeolite (Ni/BEA) catalysts activate carbon-hydrogen bonds in light alkanes, as demonstrated through isobutane reaction testing. Controlled synthesis of Ni/BEA allows for efficient introduction of ion-exchanged Ni sites at varying Ni loadings (0.43% − 1.8%). These catalysts exhibit site time yields (STY) for H2 production that increase with increasing Ni loading. A detailed analysis of secondary reactions and carbon deposition based on the relative molar flowrates of product C and H indicates that the observed increase in H2 STY with increasing Ni loading is likely attributed to both increasing alkane activation activity and increasing formation of hydrogen-deficient aromatic products retained within the catalyst pores. In situ diffuse-reflectance UV–visible-NIR absorbance and X-ray absorption spectroscopies indicate isolated, 4-coordinate Ni(2+) species for all loadings. Quantum mechanics/molecular mechanics modeling identifies two distinct Ni(2+) sites consistent with the structural characterization, but with differing relative stabilities due to their coordination environment. Computed reaction energetics for isobutane dehydrogenation demonstrate that the more stable Ni(2+) species at a six-membered 4Si-2Al ring, Ni-6MR, is less active for isobutane dehydrogenation than the less stable Ni(2+) at the five-membered 3Si-2Al ring, Ni-5MR. The differing local structure of the isolated cationic Ni sites in Ni/BEA offers a possible rationalization for the increased H2 STY observed at greater Ni loadings.

Magnetically recoverable Nd0.7Ca0.3Mn1-xNixO3 polygonal-shaped perovskite nanophotocatalysts for efficient visible-light degradation of methylene blue and tetracycline

A crucial requirement for environmental protection is the removal of carcinogenic organic pollutants from industrial effluents that are discharged into water bodies and jeopardize human health. In this study, newly designed Nd0.7Ca0.3Mn1-xNixO3 (x = 0.01–0.03) perovskite nanocomposites are proposed for the efficient photocatalytic degradation of methylene blue (MB) and tetracycline (TC) organic pollutants. Structural characterization by X-ray diffraction analysis has confirmed formation of a perovskite orthorhombic phase (Pnma) in equilibrium with an Nd2O3 secondary phase, the amount of which reduces significantly from 28 wt% for NdMnO3 to 5 wt% for the highly doped Nd0.7Ca0.3Mn0.97Ni0.03O3. Transmission electron microscopy observation has revealed polygon-shaped particles in the size range 32–56 nm. The band-gap energy was found to gradually decrease from 3.00 to 2.30 eV with increasing Ni loading. The as-prepared composites exhibit paramagnetic behavior, irrespective of the chemical composition, which facilitates simple magnetic recovery. Among the studied nanocomposites, Nd0.7Ca0.3Mn0.97Ni0.03O3 displayed the optimum photocatalytic activities for the degradation of MB (96.0%) and TC (96.6%). Its significantly enhanced photocatalytic activity can be attributed to a combination of several intrinsic characteristics, including high lattice distortion, narrow band-gap energy, a reduced electron–hole recombination rate, increased surface oxygen adsorption, and the presence of spin-polarized bands, as well as synergistic effects due to Ca/Nd substitution and Ni/Mn doping. The degradation reaction follows pseudo-first-order kinetics. Furthermore, the catalyst degrades the studied organic pollutants by at least 95%, with good stability over five consecutive reaction cycles and facile recovery without tedious purification or work-up processes. The present study demonstrates that the as-fabricated perovskite nanocomposite possesses the requisite properties for use as an efficient photocatalyst for the degradation of organic pollutants.

In-situ catalytic upgrading of coal pyrolysis volatiles over red mud-supported nickel catalysts

Red mud (RM), as a solid waste from Bayer alumina production process, has been proved its effect on upgrading of coal tar and bio-oil. In this work, a series of red mud-supported nickel (Ni/RM) catalysts was prepared by impregnation method and used for the in-situ catalytic upgrading of coal pyrolysis volatiles. The study investigated the effect of Ni loading on the physical and chemical properties of RM, the products distribution of pyrolysis process, and the components of tar. The results showed that the Ni loaded on RM, which is mainly existed as the state of Ni0, promotes the reduction of iron oxides in RM. Besides, the loading of Ni on RM increases the BET specific surface area. The changes of RM in physical and chemical properties further improve the tar quality compared to RM, and the content of heavy components (boiling point above 360 °C) in tar decreases from 27.0 wt.% with RM to 9.5 wt.% with 20Ni/RM. The highest light tar yield was obtained over 15Ni/RM as 7.7 wt.%, daf. Moreover, the presence of Ni/RM mainly increased the contents of phenols and naphthalenes and decreased those of 3-4 rings aromatics and aliphatic hydrocarbons in coal pyrolysis tar. Besides, the 15Ni/RM catalyst demonstrated stable catalytic performance after three regeneration cycles.

H2 rich gas production from agricultural waste mixture over Ni/kaolin and Ni/bentonite catalyst by gasification

Biomass gasification is an attractive technology in order to utilize agricultural waste which is the mixture of oil extracted sunflower seeds (pulp), tea, and tobacco waste. In this study, natural clay-based catalysts were synthesized using the impregnation method with the different Ni loading amounts (10, 20, 30 wt%), different support materials (kaolin and bentonite). The catalysts were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), Scanning electron microscopy (SEM), and Brunauer–Emmett–Teller analysis (BET). Gasification of biomass mixture was performed using air as the gasification agent using an updraft tubular gasifier. Studies were carried out at 650–850 °C and the time range of 15–30 min without a catalyst, and the studies with catalyst were carried out at a constant temperature of 650 °C. The highest hydrogen yield was obtained as 6.86 mol/kg biomass at 650 °C, 15 min with 30% Ni/Calcined Kaolin.

Assessing the effects of nickel on, e.g., Medicago sativa L. nodules using multidisciplinary approach.

Industrial wastes and fertilizers can introduce excessive levels of nickel (Ni) into the environment, potentially causing threats to plants, animals, as well as human beings. However, the number of studies on the effects of Ni toxicity on nodules is fairly limited. To address this issue, the effects of increasing Ni concentration on alfalfa nodules were assessed at chemical, biochemical, and transcriptomic levels. For this purpose, plants were grown in soils supplied with Ni (control, 0 mg/kg; C1, 50 mg/kg; C2, 150 mg/kg; C3, 250 mg/kg; and C4, 500 mg/kg) for 90 days. Ni loads in leaves, roots, and nodules were monitored after the exposure period. A set of biochemical biomarkers of oxidative stress was determined in nodules including antioxidants and metal homeostasis as well as lipid peroxidation. Gene expression levels of the main targets involved in oxidative stress and metal homeostasis were assessed. Our data indicated a high concentration of Ni in leaves, roots, and nodules where values reached 25.64 ± 3.04 mg/kg, 83.23 ± 5.16 mg/kg, and 125.71 ± 4.53 mg/kg in dry weight, respectively. Moreover, a significant increase in nodule biomass was observed in plants exposed to C4 in comparison to control treatment and percentage increased by 63%. Then, lipid peroxidation increased with a rate of 95% in nodules exposed to C4. Enzymatic activities were enhanced remarkably, suggesting the occurrence of oxidative stress, with increased superoxide dismutase (SOD), glutathione reductase (GR), and ascorbate peroxidase (APX). Our results showed also a significant upregulation of SOD, GR and APX genes in nodules. Nodule homoglutathione (HGSH) levels increased with the different Ni concentrations, with a remarkable decrease of glutathione S-transferase (GST) activity and glutathione (GSH) content for the highest Ni concentration with 43% and 52% reduction, respectively. The phytochelatin (PC) and metallothionein (MT) concentrations increased in nodules, which implied the triggering of a cellular protection mechanism for coping with Ni toxicity. The results suggested that Ni promotes a drastic oxidative stress in alfalfa nodules, yet the expression of MT and PC to reduce Ni toxicity could be used as Ni stress bioindicators. Our findings provide new insights into the central role of alfalfa nodules in limiting the harmful effects of soil pollution. Therefore, nodules co-expressing antioxidant enzymes may have high phytoremediation potential.

A multi-pronged approach to source attribution and apportionment of heavy metals in urban rivers.

Heavy metal (HM) contamination of water bodies is caused by both first generation (industries) and second generation (distributed sources, domestic sewage, sediments) sources. We applied a multi-pronged approach to quantify the contribution of first and second generation sources to the HM load in a stream located in an industrialised catchment. We found that, despite strict regulation, first generation sources contributed significantly to the HM load (60%-80%), showing the ineffectiveness of current regulation. Domestic sewage contributed significantly to Cu, Ni, and Mn load (15%-20%). The contribution of distributed sources and sediments to HM load is insignificant. In a 24-hour cycle, HM concentrations frequently exceeded FAO's irrigation water quality standards, with the highest concentrations observed at night. Empirically, the study highlights the continued plight of urban streams in rapidly industrialising centers and the failure to regulate first-generation sources. Methodologically, it demonstrates the importance of temporally intensive measurement of contaminant concentration and load. Policy implications include the need for ambient water quality standards, inclusion of HMs in such standards, load-based regulation, and a problem-oriented monitoring and enforcement approach.

Ni-modified dolomite for the catalytic deoxygenation of pyrolyzed softwood and non-wood to produce bio-oil

This study investigated the effect of process conditions during the catalytic pyrolysis of softwood and non-wood on the pyrolysis product. Ni modified on calcined dolomite (Ni-DM) was used to determine the effectiveness of the catalytic activity and the effect of doping non-noble metals on the product distribution of both pyrolyzed biomasses. The lignocellulosic biomass components showed different effects on the decomposition characteristics of the pyrolysis vapor and its devolatilization, while Ni-DM showed a catalytic effect to enhance the decarbonylation, decarboxylation, and secondary reaction of tar cracking affecting CO2 and CO removal; additionally, the catalytic activity also promoted the formation of aliphatic and olefin hydrocarbon compounds and facilitated C–C cleavage and scission to smaller hydrocarbon compounds. With increased Ni loading, the yield of noncondensable gas increased. Furthermore, gas chromatography analysis indicated that the composition of gas mainly consisted of hydrogen gas, which increased significantly due to a water-gas shift during the catalytic pyrolysis of biomass at high temperature with 10% Ni-dispersed calcined dolomite acting as the catalyst. Meanwhile, the pore structure and the modified-Ni on calcined dolomite enhance decrease acids and sugars in bio-oil yield and favor the formation of alkane gases of liquid hydrocarbon fuels including the dramatically increased in alkane gases.

Developing Benign Ni/g-C3N4 Catalysts for CO2 Hydrogenation: Activity and Toxicity Study.

This research discusses the CO2 valorization via hydrogenation over the non-noble metal clusters of Ni and Cu supported on graphitic carbon nitride (g-C3N4). The Ni and Cu catalysts were characterized by conventional techniques including XRD, AFM, ATR, Raman imaging, and TPR and were tested via the hydrogenation of CO2 at 1 bar. The transition-metal-based catalyst designed with atom-economy principles presents stable activity and good conversions for the studied processes. At 1 bar, the rise in operating temperature during CO2 hydrogenation increases the CO2 conversion and the selectivity for CO and decreases the selectivity for methanol on Cu/CN catalysts. For the Ni/CN catalyst, the selectivity to light hydrocarbons, such as CH4, also increased with rising temperature. At 623 K, the conversion attained ca. 20%, with CH4 being the primary product of the reaction (CH4 yield >80%). Above 700 K, the Ni/CN activity increases, reaching almost equilibrium values, although the Ni loading in Ni/CN is lower by more than 90% compared to the reference NiREF catalyst. The presented data offer a better understanding of the effect of the transition metals’ small metal cluster and their coordination and stabilization within g-C3N4, contributing to the rational hybrid catalyst design with a less-toxic impact on the environment and health. Bare g-C3N4 is shown as a good support candidate for atom-economy-designed catalysts for hydrogenation application. In addition, cytotoxicity to the keratinocyte human HaCaT cell line revealed that low concentrations of catalysts particles (to 6.25 μg mL–1) did not cause degenerative changes.

Ni-CeO2 Catalyst with High Ni Loading Prepared by Salt-Assisted Solution Combustion for CO2 Methanation

An Ni-CeO2 catalyst with high Ni loading (50 wt.%) prepared by a salt-assisted solution combustion method was characterized by different methods and used for CO2 methanation. The specific surface area of the Ni-CeO2 catalyst prepared by salt-assisted solution combustion is 7 times that of the catalyst prepared by conventional solution combustion. The Ni-CeO2 catalyst prepared by salt-assisted solution combustion has smaller particle sizes of Ni and exhibits excellent activity at low temperatures. The high Ni loading and small Ni particle size can provide more metal Ni site and Ni-CeO2 interface, which help to improve the CO2 methanation performance.

Anchoring single Ni atoms on CeO2 nanospheres as an efficient catalyst for the hydrogenolysis of lignin to aromatic monomers

Lignin is the most abundant renewable aromatic resource in nature; thus, the development of an efficient and economical catalysts that can depolymerize lignin into value-added aromatic monomers is highly desirable. Here, we report a single-atom Ni catalyst (xNi/CeO2-S, where x represents the Ni loading), in which the single-atom Ni sites are anchored to the oxygen vacancies on CeO2 nanospheres, for the conversion of cellulolytic enzyme lignin (CEL) via depolymerization and hydrodeoxygenation. The 1.0Ni/CeO2-S catalyst performed the best, achieving a lignin oil (LO) and maximum monomer yield of 84.3 wt% and 32.6 wt%, respectively; a higher heat value of 31.64 MJ/Kg is achieved for LO compared to 23.03 MJ/Kg for CEL. Thus, single-atom nickel catalyst exhibited excellent activity and stability in promoting the depolymerization of lignin. These results validate the viability of single-atom metal catalysts for the conversion of lignin resources.

Interfacial interaction-dependent in situ restructure of NiO/TiO2 photocatalysts

Composite photocatalysts often undergo in situ restructure during photocatalytic reactions. Herein we report that the NiO-TiO2 interfacial interaction of NiO/TiO2 photocatalysts prepared via an ion exchange method strongly influences in situ restructure processes. With the Ni loading increasing, TiO2 supported NiO nanoparticles, TiO2 (core)-NiO (ultrathin shell) and TiO2 (core)-NiO (ultrathin shell) supported NiO nanoparticles are acquired sequentially. During photocatalytic water reduction reaction, TiO2 supported NiO nanoparticles and TiO2 (core)-NiO (ultrathin shell) are stable due to strong NiO-TiO2 interfacial interaction, whereas NiO nanoparticles supported on TiO2 (core)-NiO (ultrathin shell) are reduced to Ni nanoparticles, resulting enhanced photocatalytic activity. These findings bridge heterogeneous thermocatalysis and photocatalysis with the phenomenon of interfacial interaction-dependent in situ restructure.