Mesoporous carbon-supported cobalt catalyst for selective oxidation of toluene and degradation of water contaminants

Mesoporous carbon-supported cobalt (Co-MC) catalysts are widely applied as electrode materials for batteries. Conversely, the development of Co-MC as bifunctional catalysts for application in organic catalytic reactions and degradation of water contaminants is slower. Herein, the catalyst displayed high activity in the selective oxidation of toluene to benzaldehyde under mild conditions, attaining a high selectivity of 92.3%. Factors influencing the catalytic reaction performance were also investigated. Additionally, Co-MC displayed remarkable catalytic activity in degrading dyes relative to the pure metal counterpart. Moreover, the catalyst exhibited excellent reusability, as determined by the cyclic catalytic experiments. The paper demonstrates the potential of Co-MC as a bifunctional catalyst for both toluene selective oxidation and water contaminant degradation.     

CATALYTIC PROPERTIES OF NANOFIBROUS CARBON IN SELECTIVE OXIDATION OF HYDROGEN SULPHIDE

Nanofibrous carbonaceous materials （NFC） as a new class of materials having many applications, can catalyze the selective oxidation of H2S to sulfur. The correlation between NFC structure and its activity and selectivity in H2S oxidation was determined. It is demonstrated that selectivity can be improved if NFC with more ordered structure be synthesized and the portion of the original catalyst in carbon be reduced by increasing the carbon accumulated in the catalyst.     

CARBON NANOTUBES VIA METHANE DECOMPOSITION ON AN ALUMINA SUPPORTED COBALT AEROGEL CATALYST

An alumina-supported cobalt aerogel catalyst prepared from a sol-gel and a supercritical drying method was used in the catalytic decomposition of methane.The physical-chemical properties of the catalyst were characterized and its activity for methane decomposition was investigated.The effects of calcination and reaction temperatures on the activity of the catalyst and the morphology of the carbon nanotubes produced were discussed.A COAl2O4 spinel structure formed in the calcined catalyst.The quantity of the nanotubes produced in the reaction increases with the amount of cobalt in the reduced catalyst.A higher reaction temperature leads to a higher reaction rate,though faster deactivation of the catalyst occurs with the change.The carbon nanotubes grown on the catalyst have smooth walls and uniform diameter distribution.     

Converting industrial waste contact masses into effective multicomponent copper-based catalysts for the Rochow process

In this work, we report a simple and inexpensive approach to synthesize effective multicomponent Cu–Cu₂O–CuO catalysts for the Rochow process from industrial waste contact masses (WCMs). WCMs from the organosilane industry were treated with acid followed by reduction with metallic iron powder. The obtained copper powder was then subjected to controlled oxidation in air at different temperatures, followed by ball milling. The orthogonal array approach was applied to optimize this process, and the stirring speed and pH were found to significantly affect the leaching ratio and copper yield, respectively. When used for the Rochow process, the optimized ternary Cu–Cu₂O–CuO catalyst greatly enhanced the dimethyldichlorosilane selectivity and Si conversion compared with Cu–Cu₂O–CuO catalysts prepared without ball milling, bare Cu catalysts, and Cu–Cu₂O–CuO catalysts with different compositions. This could be attributed to their small particle size and the strong synergistic effect among the multiple components in the catalyst with the optimized composition.     

Inverted-design for highly-active hydrogen evolution electrocatalyst of MoS2@Ni3S2 core-shell via unlocking the potential of Mo

Through inverted-design rather than modifying the generally-assumed S active sites in popular MoS₂, we unlock the potential of Mo sites and successfully prepared novel MoS₂@Ni₃S₂/NF core-shell nanospheres as a catalyst for the high-performance hydrogen evolution reaction (HER). The ΔG_H at the Mo site is optimized via Ni₃S₂ to achieve excellent HER activity. At low current densities, it has similar activity to the Pt/C. However, its performance is better than Pt/C at high density. Moreover, our catalyst shows a considerable stability at a variety of current densities for 50 h, promising to substitute noble metal catalysts in application of commercial alkaline electrocatalysts.     

High-throughput synthesis of size-controlled Pt-based catalysts

Pt catalysts are commonly used for chemical reaction processes due to its high catalytic activity and selectivity. Notably, the size of metal particles often has a significant impact on the performance of the metal-loaded catalysts. Therefore, developing highly efficiently synthesis method for the size control of Pt catalysts has great development prospects and research value. In this study, high-throughput size tuning of Pt-based catalysts was achieved by carbonizing the carriers. The experimental and characterization results showed that the size of the loaded Pt nanoparticles varied with different concentrations of glucose solution during carriers carbonization process. The reduction of 4-nitrophenol as a template reaction indicated that the reaction rate constant of the catalyst is approximately linear with the size of Pt particles. Importantly, a laboratory-built high-throughput synthesis system was applied for the catalyst synthesis, which enhances the automation of the laboratory exploratory experiments and makes it possible to synthesize catalysts with controllable size in batches.     

Secondary reduction strategy synthesis of Pt–Co nanoparticle catalysts towards boosting the activity of proton exchange membrane fuel cells

Based on the volcanic relationship between catalytic activity and key adsorption energies, Pt–Co alloy materials have been widely studied as cathode oxygen reduction reaction (ORR) catalysts in proton exchange membrane fuel cells (PEMFCs) due to their higher active surface area and adjustable D-band energy levels compared to Pt/C. However, how to balance the alloying degree and ORR performance of Pt–Co catalyst remains a great challenge. Herein, we first synthesized a well-dispersed Pt/Co/C precursor by using a mild dimethylamine borane (DMAB) as the reducing agent. The precursor was calcined at high temperature under H₂/Ar mixed gas by a secondary reduction strategy to obtain an ordered Pt₃Co intermetallic compound nanoparticle catalyst with a high degree of alloying. The optimization of electronic structure due to Pt–Co alloying and the strong metal-carrier interaction ensure the high kinetic activity of the cell membrane electrode. Additionally, the high degree of graphitization increases the electrical conductivity during the reaction. As a result, the activity and stability of the catalyst were significantly improved, with a half-wave potential as high as 0.87 V, which decreased by only 20 mV after 10000 potential cycles. Single-cell tests further validate the high intrinsic activity of the ordered Pt₃Co catalyst with mass activity up to 0.67 A mg_pt⁻¹, exceeding the United States Department of Energy (US DOE) standard (0.44 A mg_pt⁻¹), and a rated power of 5.93 W mg_pt⁻¹.     

Lithium-storage properties of SiO2 nanotubes@C using carbon nanotubes as templates

Silica-based anode material is the most concerned material at present, which has the advantages of good cycle stability, high theoretical specific capacity and abundant reserves. However, silica suffers from inherent low conductivity, severe volume expansion effect and low initial coulombic efficiency, which limits its application in lithium-ion batteries. Nanotubes structure can mitigate the volume expansion during lithiation/delithiation. In this article, silica nanotubes (SNTs) were prepared using carbon nanotubes (CNTs) as a template, and then the uniform carbon layer was coated on their surface by carbonization of citric acid. The hollow structure of nanotubes provides more sites for the insertion of Li⁺ during lithiation and additional channels for Li⁺ migration in the cycles, which improves the electrochemical performance. Conductivity can be enhanced by coating carbon layer. The specific capacity of the composite material is about 650 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles. With a specific capacity of 400 mAh g⁻¹ even at 1 A g⁻¹ after 100 cycles. The silica-based material is a competitive anode material for lithium-ion batteries.     

Preparation of bunched CeO2 and study on microwave absorbing properties with MWCNTs binary composite

A novel bunched cerium oxide (CeO₂) was prepared and its binary composite material with multi-walled carbon nanotubes presented an excellent microwave absorbing properties. The morphology, structure, and absorbing properties of the composite material were investigated. It was found that the minimum reflection loss (RL) of the composite material at 15.79 GHz was −45.7 dB when the thickness was 5.5 mm. It was worth noting that when the composite material was in the thickness range of 5.0–7.5 mm and the frequency was 11.36–17.77 GHz, the electromagnetic wave RL was < −30 dB, which illustrated that the composite material had a good absorbing effect over a wide thickness range. The results of the study contributed to the design and preparation of efficient microwave absorbing materials (MAM) with rare earth oxide composites and their applications, which demonstrated the importance of new composites with special structures in the field of MAM.     

CATALYST TECHNOLOGY DEVELOPMENT FROM MACRO-, MICRO- DOWN TO NANO-SCALE

Catalyst and catalytic process technology has been an ever-growing field that involves chemical engineering, chemistry, and material science. A number of excellent review articles and books have been published on the subject. In this work, the author reviews the evolution and development of catalyst products with multi-scale methodology. The catalyst technologies are classified into three levels, macro-scale （reactor size）, mini-and micro-scale （catalyst unit）, and nano-scale （catalyst intrinsic structures）. Innovation at different scales requires different sets of expertise, method, and knowledge. Specific examples of significant impact to practical application are used to illustrate technology development at each scale. The multi-scale analysis enables clear delineation of technology components and their relationship for a catalyst product and catalytic process. Manipulation of catalyst structures at nano-scale to increase intrinsic activity and/or selectivity is considered of large potential for future catalyst product development. Recent research results on Cu-CeO2 and Au-CeO2 composite catalysts for air pollution control and hydrogen production are used to show how novel catalytic properties can be discovered by unique combination of different but common materials at the nano-scale.     

INTERACTION-MEDIATED GROWTH OF CARBON NANOTUBES ON ACICULAR SILICA-COATED a-Fe CATALYST BY CHEMICAL VAPOR DEPOSITION BY CHEMICAL VAPOR DEPOSITION

1. Introduction Carbon nanotubes (CNTs), a kind of the most advanced nanomaterials with novel properties and promising for many applications, have aroused great interest of the world in a number of research fields (Iijima, 1991; Baughman et al., 2002; Iijima & Ichihashi, 1993; Rao & Govindaraj, 2002; Rueckes et al., 2000; Adrian et al., 2001; Javey et al., 2003). Catalytic chemical vapor deposition (CCVD) is re-garded as the most suitable method for the preparation of microstructured CN…     

Control of iron nanoparticle size by manipulating PEG–ethanol colloidal solutions and spin-coating parameters for the growth of single-walled carbon nanotubes

Iron catalyst nanoparticles were prepared on silicon wafers by spin-coating colloidal solutions containing iron nitrate, polyethylene glycol (PEG) and absolute ethanol. The effects of various spin-coating conditions were investigated. The findings showed that the size of the iron particles was governed by the composition of the colloidal solution used and that a high angular speed was responsible for the formation of a thin colloidal film. The effect of angular acceleration on the size and distribution of the iron particles were found to be insignificant. It was observed that a longer spin-coating duration provoked the agglomeration of iron particles, leading to the formation of large particles. We also showed that single-walled carbon nanotubes could be grown from the smallest iron catalyst nanoparticles after the chemical vapor deposition of methane.     

INTERACTION-MEDIATED GROWTH OF CARBON NANOTUBES ON ACICULAR SILICA-COATED α-Fe CATALYST BY CHEMICAL VAPOR DEPOSITION

Multi-walled carbon nanotubes (MWNTs) with 20 nm outer diameter were prepared by chemical vapor deposition of ethylene using ultrafine surface-modified acicular α-Fe catalyst particles.The growth mechanism of MWNTs on the larger catalyst particles are attributed to the interaction between the Fe nanoparticles with the surface-modified silica layer.This interaction-mediated growth mechanism is illustrated by studying the electronic,atomic and crystal properties of surface-modified catalysts and MWNTs products by characterization with X-ray diffraction (XRD),transmission electron microscopy (TEM),high resolution transmission electron microscopy (HRTEM),thermal gravimetric analysis (TGA) and Raman spectra.     

Catalytic oxidation of benzene over Ce–Mn oxides synthesized by flame spray pyrolysis

Flame spray pyrolysis (FSP) was utilized to synthesize Ce–Mn oxides in one step for catalytic oxidation of benzene. Cerium acetate and manganese acetate were used as precursors. The materials synthesized were characterized using X-ray diffraction (XRD), N₂ adsorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and H₂-temperature programmed reduction (H₂-TPR) and their benzene catalytic oxidation behavior was evaluated. Mn ions were evidenced in multiple chemical states. Crystalline Ce–Mn oxides consist of particles with size <40 nm and specific surface areas (SSA) of 20–50 m²/g. Raman spectrums and H₂-TPR results indicated the interaction between cerium and manganese oxides. Flame-made 12.5%-Ce–Mn oxide exhibited excellent catalytic activity at relatively low temperatures (T₉₅ about 260 °C) compared to other Ce–Mn oxides with different cerium-to-manganese ratios. Redox mechanism and strong interaction conform to structure analysis that Ce–Mn strong interaction formed during the high temperature flame process and the results were used to explain catalytic oxidation of benzene.     

Regeneration of spent catalysts in oxy-combustion atmosphere

The feasibility of adopting an oxy-combustion stage to regenerate a spent catalyst proposed for methane thermo-catalytic decomposition has been investigated in a laboratory scale bubbling fluidized bed reactor operated at 800 °C and different inlet oxygen concentrations. The efficiency of carbon oxy-combustion regeneration strategy has been evaluated on the basis of the efficiency of carbon removed from the catalyst and the performance of regenerated catalyst. The effect of multiple cycles of decomposition and regeneration steps has been also quantified. Experimental activity confirmed the possibility of producing a CO₂ stream that can be finalized to a sequestration unit but also indicated the requirement of a good temperature control of catalytic particles.     

TiO2-modified nano-egg-shell Pd catalyst for selective hydrogenation of acetylene

Pd-based egg-shell nano-catalysts were prepared using porous hollow silica nanoparticles(PHSNs)as support,and the as-prepared catalysts were modified with TiO2 to promote their selectivity for hydrogenation of acetylene.Pd nanoparticles were loaded evenly on PHSNs and TiO2 was loaded on the active Pd particles.The effects of reduction time and temperature and the amount of TiO2 added on catalytic performances were investigated by using a fixed-bed micro-reactor.It was found that the catalysts showed better performance when reduced at 300 C than at 500 C,and if reduced for 1h than 3h.When the amount of Ti added was 6 times that of Pd,the catalyst showed the highest ethylene selectivity.     

Temperature evolution on Rh/Al2O3 catalyst during partial oxidation of methane in a reverse flow reactor

Catalytic partial oxidation of methane was investigated in a reverse flow reactor with commercial Rh/Al₂O₃ catalyst in pellets. The process is carried out in a catalytic fixed bed reactor and switching of feed flow direction is obtained through four electrovalves synchronized in pairs. Temperature profile along the catalyst bed was measured by fast IR thermography and product composition was measured with a continuous gas analyzer.Feed direction switching time, water to methane ratio and inert section length were investigated as process parameters.Data of catalyst bed temperature evolution during the flow cycle are presented, discussed and related to reactor performance as a function of reverse flow switching period.The effect of water addition to the reacting mixture on the dynamics of catalyst bed temperature evolution is also presented.     

Investigation of stress-strain behavior of single walled carbon nanotube/rubber composites by a multi-scale finite element method

The excellent properties of carbon nanotubes have generated technological interests in the development of nanotube/rubber composites. This paper describes a finite element formulation that is appropriate for the numerical prediction of the mechanical behavior of rubber-like materials which are reinforced with single walled carbon nanotubes. The considered composite material consists of continuous aligned single walled carbon nanotubes which are uniformly distributed within the rubber material. It is assumed that the carbon nanotubes are imperfectly bonded with the matrix. Based on the micromechanical theory, the mechanical behavior of the composite may be predicted by utilizing a representative volume element. Within the representative volume element, the reinforcement is modeled according to its atomistic microstructure. Therefore, non-linear spring-based line elements are employed to simulate the discrete geometrical structure and behavior of the single-walled carbon nanotube. On the other hand, the matrix is modeled as a continuum medium by utilizing solid elements. In order to describe its behavior an appropriate constitutive material model is adopted. Finally, the interfacial region is simulated via the use of special joint elements of variable stiffness which interconnect the two materials in a discrete manner. Using the proposed multi-scale model, the stress-strain behavior for various values of reinforcement volume fraction and interfacial stiffness is extracted. The influence of the single walled carbon nanotube addition within the rubber is clearly illustrated and discussed.     

Using waste to treat waste: Red mud induced hierarchical porous γ-AlOOH and γ-Al2O3 microspheres as superior Pd support for catalytic reduction of 4-nitrophenol

Toward the imperative treatment of the industrial wastewater containing 4-nitrophenol (4-NP) and industrial solid waste red mud (RM), an innovative approach of “Using waste to treat waste” is developed. Valuable element Al is leached from the RM first, the resultant NaAlO₂ solution is hydrothermally converted to γ-AlOOH hierarchical porous microspheres (RM γ-AlOOH HPMSs, average diameter: 2.0 μm, S_BET: 77.81 m² g⁻¹, pore volume: 0.38 cm³ g⁻¹) in the presence of urea. The subsequent mild thermal conversion results in γ-Al₂O₃ hierarchical porous microspheres (RM γ-Al₂O₃ HPMSs). Both of the RM γ-AlOOH and RM γ-Al₂O₃ HPMSs are employed as the Pd catalyst support for the catalytic reduction of 4-NP. Particularly, the as-obtained composite Pd/RM γ-AlOOH and Pd/RM γ-Al₂O₃ exhibit excellent catalytic activities with superior k_nor as 8204.5 and 4831.4 s⁻¹ g⁻¹, respectively, significantly higher than that of most Pd based catalysts. Moreover, the excellent catalytic stability and durability of the Pd/RM γ-AlOOH and Pd/RM γ-Al₂O₃ within 10 successive cycles of reduction enable the present industrial solid waste RM induced γ-AlOOH and γ-Al₂O₃ HPMSs as great promising Pd catalyst support for the reduction of the industrial wastewater containing 4-NP.     

Interaction between Weibull parameters and mechanical strength reliability of industrial-scale water gas shift catalysts

A fundamental step in the production of an industrial catalyst is its crushing strength assessment. Limited literature exists in which the strength reliability of supported catalysts is investigated from production to their application in a reactor. In this work, cylindrical supports were prepared by pelletizing high porosity γ-alumina powder, and Cu–Zn/γ-Al₂O₃ catalysts were prepared by impregnation of the pelletized γ-alumina supports with an aqueous solution of copper and zinc nitrates. The support-forming variables, such as binder concentration, compaction pressure, calcination temperature, and drying procedure were investigated. The Weibull method was used to analyze the crushing strength data of the supports, and the fresh and used catalysts before and after the low-temperature water gas shift reaction. Support formation at a 50 wt% binder concentration, 1148 MPa compaction pressure, 500 °C calcination temperature, and rapid drying (100 °C, 8 h) led to the maximum support mechanical reliability. The most reliable catalyst with respect to simultaneous appropriate catalytic performance and mechanical strength was prepared from a support with the lowest mean crushing strength (26.25 MPa). This work illustrates the importance of the Weibull modulus as a useful mechanical reliability index in manufacturing a supported solid catalyst.