Preparation of mesoporous activated carbons from coal liquefaction residue for methane decomposition

Mesoporous activated carbons were prepared from direct coal liquefaction residue （CLR） by KOH activation method, and the experiments were carried out to investigate the effects of KOH/CLR ratio, solvent for mixing the CLR and KOH, and carbonization procedure on the resultant carbon texture and catalytic activity for catalytic methane decomposition （CMD）. The results showed that optimal KOH/CLR ratio of 2 ： 1; solvent with higher solubility to KOH or the CLR, and an appropriate carbonization procedure are conductive to improving the carbon pore structure and catalytic activity for CMD. The resultant mesoporous carbons show higher and more stable activity than microporous carbons. Additionally, the relationship between the carbon textural properties and the catalytic activity for CMD was also discussed.

Bi-metallic catalysts of mesoporous Al_2O_3 supported on Fe, Ni and Mn for methane decomposition: Effect of activation temperature

Methane decomposition reaction has been studied at three different activation temperatures（500℃,800℃ and950℃）over mesoporous alumina supported Ni–Fe and Mn–Fe based bimetallic catalysts.On co-impregnation of Ni on Fe/Al2O3the activity of the catalyst was retained even at the high activation temperature at 950℃ and up to180 min.The Ni promotion enhanced the reducibility of Fe/Al2O3oxides showing higher catalytic activity with a hydrogen yield of 69%.The reactivity of bimetallic Mn and Fe over Al2O3catalyst decreased at 800℃ and 950℃ activation temperatures.Regeneration studies revealed that the catalyst could be effectively recycled up to 9times.The addition of O2（1 ml,2 ml,4 ml）in the feed enhanced substantially CH4conversion,the yield of hydrogen and the stability of the catalyst.

Influences of reaction conditions on methane decomposition over non-supported Ni catalyst

Effects of reaction temperature and methane gas hourly space velocity （GHSV） on methane decomposition over non-supported Ni catalyst have been investigated in this work.Methane molecules activation,Ni particles growth and nano-carbon diffusion were the main factors influencing methane decomposition stability of non-supported Ni.The results of methane decomposition activity test on the non-supported Ni catalyst showed that the prepared non-supported Ni could exhibit a good methane decomposition performance with 273 gC/gNi and 2667 molH2/molNi at 500 -C and 45000 mL/（gcat h）.Scanning electron microscope （SEM）,X-ray powder diffraction （XRD） and temperature-programmed oxi- dation （TPO） have been carried out to characterize the used catalysts.The deposited carbon was carbon nanofibers,among which graphitic carbon formation increased with the reaction time of methane decomposition.Ni particle size was not the decisive factor during the carbon growing stage.

Effect of surface structure on the catalytic behavior of Ni:Cu/Al and Ni:Cu:K/Al catalysts for methane decomposition

Methane decomposition using nickel, copper, and aluminum （Ni：Cu/Al） and nickel, copper, potassium, and aluminum （Ni：Cu：K/Al） modified nano catalysts has been investigated for carbon fibers, hydrogen and hydrocarbon production. X-ray photoelectron spectroscopy （XPS）, static secondary ion mass spectrometry （SSIMS）, thermal gravimetric analysis （TGA）, Fourier transform infrared （FT-IR）, secondary electron microscopy/X-ray energy dispersive （SEM-EDX）, and temperature programmed desorption （TPD） were used to depict the chemistry of the catalytic results. These techniques revealed the changes in surface morphology and structure of Ni, Cu, Al, and K, and formation of bimetallic and trimetallic surface cationic sites with different cationic species, which resulted in the production of graphitic form of pure carbon on Ni：Cu/Al catalyst. The addition of K has a marked effect on the product selectivity and reactivity of the catalyst system. K addition restricts the formation of carbon on the surface and increases the production of hydrogen and C2, C3 hydrocarbons during the catalytic reaction whereas no hydrocarbons are produced on the sample without K. This study completely maps the modified surface structure and its relationship with the catalytic behavior of both systems. The process provides a flexible route for the production of carbon fibers and hydrogen on Ni：Cu/Al catalyst and hydrogen along with hydrocarbons on Ni：Cu：K/Al catalyst. The produced carbon fibers are imaged using a transmission electron microscope （TEM） for diameter size and wall structure determination. Hydrogen produced is COx free, which can be used directly in the fuel cell system. The effect of the addition of Cu and its transformation and interaction with Ni and K is responsible for the production of CO/CO2 free hydrogen, thus producing an environmental friendly clean energy.

Growth of Aligned Carbon Nanotubes on Large Scale by Methane Decomposition with Deactivation Inhibitor

The effects of additives containing iron or nickel during chemical vapor deposition （CVD） on the growth of carbon nanotubes （CNTs） by methane decomposition on Mo/MgO catalyst were investigated. Ferrocene and nickel nitrate were introduced as deactivation inhibitors by in-situ evaporation during CVD. The precisely controlled in-situ introduction of these inhibitors increased the surface renewal of catalyst, and therefore prevented the catalyst from deactivation. Using this method, aligned multi-walled CNTs with parallel mesopores can be produced on a large scale.

Methane Decomposition into Carbon Fibers over Coprecipitated Nickel-Based Catalysts

Decomposition of methane in the presence of coprecipitated nickel-basedcatalysts to produce carbon fibers was investigated. The reaction was studied in the temperaturerange of 773 K to 1073 K. At 1023 K, the catalytic activities of three catalysts kept high at theinitial period and then decreased with the reaction time. The lifetimes of Ni-Cu-Al and Ni-La-Alcatalysts are longer than that of Ni-Al catalyst. With three catalysts, the yield of carbon fiberswas very low at 773 K. The yield of carbon fibers for Ni-La-Al catalyst was more than those forNi-Al and Ni-Cu-Al catalysts. For Ni-La-Al catalyst, the elevation of temperature from 873 K up to1073 K led gradually to an increase in the yield of carbon fibers. XRD studies on the Ni-La-Alcatalyst indicate that La_2NiO_4 was formed. The formation of La_2NiO_4 is responsible for theincrease in the catalytic lifetime and the yield of carbon fibers synthesized on Ni-La-Al at773-1073 K. Carbon fibers synthesized on Ni-Al catalyst are thin, long carbon nanotubes. There arebamboo-shaped carbon fibers synthesized on Ni-Cu-Al catalyst. Carbon fibers synthesized on Ni-La-Alcatalyst have large hollow core, thin wall and good graphitization.

Catalytic decomposition of methane to produce hydrogen:A review

The increasing demands of hydrogen and the recent discovery of large reserves of methane have prompted the conversion of methane to hydrogen.The challenges raised by intensive CO_(2) emission from the traditional conversion of methane have provoked emission-free hydrogen production from methane.The catalytic decomposition of methane(CDM) to produce hydrogen and advanced carbon hence comes into consideration due to the short process and environmental benignity.Although many researchers have made considerable progress in CDM research on the laboratory scale,CDM is still in its infancy in industrialization.The history of its development,fundamental mechanisms,and recent research progress in catalysts and catalytic systems are herein highlighted.The problems of catalytic interface degradation are reviewed,focusing on deactivation from coke deposition in the CDM process.The introduction of a liquid phase interface which can in-situ remove carbon products provides a new strategy for this process.Furthermore,the challenges and prospects for future research into novel CDM catalysts or catalyst systems are included.

Rare earth modified Ni-Si catalysts for hydrogen production from methane decomposition

Different rare earth （RE=La, Ce, Pr, Nd, Sm, Y） and Cu modified nickel catalysts for hydrogen production from meth-ane decomposition were synthesized by a sol-gel process and method. The catalysts were characterized or analyzed through Brumauer-Emmett-Teller （BET）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） techniques. And the hydrogen production performance was also evaluated by a fixed-bed and micro-reaction technique with CH4→C＋H2 as a probe reaction. The results showed that rare earth modification had played a great role for nickel catalysts, for example, smaller nickel particles, good thermal stability, high activity, etc. La was the best additive among rare earth modification. The SEM of rare earth modified catalysts showed ordered flower-like structure and rare earth modification made the nickel particles move to the surface of catalysts. In addition, the SEM of nano-carbons was also changed by rare earth modification with long, narrow nano-carbon fibers or tubes obtained. Solid carbon formation was prevented by rare earth modification.

CO_x-Free Hydrogen and Carbon Nanofibers Produced from Direct Decomposition of Methane on Nickel-Based Catalysts

Direct decomposition of methane was carried out using a fixed-bed reactor at 700 ℃ for the production of COx-free hydrogen and carbon nanofibers. The catalytic performance of NiO-M/SiO2 catalysts （where M=AgO, CoO, CuO, FeO, MnOx and MoO） in methane decomposition was investigated. The experimental results indicate that among the tested catalysts, NiO/SiO2 promoted with CuO give the highest hydrogen yield. In addition, the examination of the most suitable catalyst support, including Al2O3, CeO2, La2O3, SiO2, and TiO2, shows that the decomposition of methane over NiO-CuO favors SiOx support. Furthermore, the optimum ratio of NiO to CuO on SiO2 support for methane decomposition was determined. The experimental results show that the optimum weight ratio of NiO to CuO fell at 8：2 （w/w） since the highest yield of hydrogen was obtained over this catalyst.

Preparation of bimetallic catalysts Ni-Co and Ni-Fe supported on activated carbon for methane decomposition

Bimetallic catalysts(Ni-Co/AC and Ni-Fe/AC)supported on activated carbon(AC)were prepared via one-step method from coal as AC precursor with the addition of metal salts by KOH activation.The effects of the introduction of second metal(Co or Fe)into Ni/AC on the textural structure of the resultant bimetallic catalysts and their catalytic performances for methane decomposition were investigated.The results showed that active metals can be directly supported on AC by the reaction of metal species with carbon during the activation.The addition of Co or Fe to Ni/AC resulted in the decrease of specific surface area and pore volume.With increasing the loading of Co or Fe,metal alloys were formed and total surface area and pore volume declined,but the mesoporosity was increased.Bimetallic Ni-Co/AC and Ni-Fe/AC catalysts exhibited better catalytic activity and stability for methane decomposition compared than Ni/AC.The introduction of Co mainly improved initial catalytic activity;however,Ni-Fe/AC catalyst showed better behaviors in terms of reducing the deactivation rate of Ni-based catalyst than Ni-Co/AC catalyst,which is relative with the formation of Ni-Fe alloy and carbon fibers over Ni-Fe/AC.This work provides a simple and efficient approach to improve catalytic performances of Ni-based catalyst for methane decomposition.

Catalytic decomposition of CH_4 over Ni-Al_2O_3-SiO_2 catalysts:Influence of pretreatment conditions for the production of H_2

This article reports the production of COx free hydrogen and carbon nanofibers by the catalytic decomposition of methane over Ni-Al2O3-SiO2 catalysts. The influence of reaction temperature, pretreatment temperature, and effect of reductive pretreatment on the decomposition of methane activity is investigated. The physico-chemical characteristics of fresh and deactivated samples were characterized using BET-SA, XRD, TPR, SEM/TEM, CHNS analyses and correlated with the methane decomposition results obtained. The Ni-Al-Si （4 ： 0.5 ： 1.5） catalyst reduced with hydrazine hydrate produced better H2 yields of ca. 1815 mol H2/mol Ni than the catalyst reduced with 5% H2/N2.

Dendritic nanoarchitecture imparts ZSM-5 zeolite with enhanced adsorption and catalytic performance in energy applications

The development of zeolites possessing dendritic features represents a great opportunity for the design of novel materials with applications in a large variety of fields and,in particular,in the energy sector to afford its transition towards a low carbon system.In the current work,ZSM-5 zeolite showing a dendritic3D nanoarchitecture has been synthesized by the functionalization of protozeolitic nanounits with an amphiphilic organosilane,which provokes the branched aggregative growth of zeolite embryos.Dendritic ZSM-5 exhibits outstanding accessibility arising from a highly interconnected network of radially-oriented mesopores(3-10 nm)and large cavities(20-80 nm),which add to the zeolitic micropores,thus showing a well-defined trimodal pore size distribution.These singular features provide dendritic ZSM-5 with sharply enhanced performance in comparison with nano-and hierarchical reference materials when tested in a number of energy related applications,such as VOCs(toluene)adsorption(improved capacity),plastics(low-density polyethylene)catalytic cracking(boosted activity)and hydrogen production by methane catalytic decomposition(higher activity and deactivation resistance).

Synthesis of multi-walled carbon nanotubes using CoMnMgO catalysts through catalytic chemical vapor deposition

The Co Mg O and Co Mn Mg O catalysts are prepared by a co-precipitation method and used as the catalysts for the synthesis of carbon nanotubes（CNTs） through the catalytic chemical vapor deposition（CCVD）. The effects of Mn addition on the carbon yield and structure are investigated. The catalysts are characterized by temperature programmed reduction（TPR） and X-ray diffraction（XRD） techniques, and the synthesized carbon materials are characterized by transmission electron microscopy（TEM） and thermo gravimetric analysis（TG）. TEM measurement indicates that the catalyst Co Mg O enclosed completely in the produced graphite layer results in the deactivation of the catalyst. TG results suggest that the Co Mn Mg O catalyst has a higher selectivity for CNTs than Co Mg O. Meanwhile, different diameters of CNTs are synthesized by Co Mn Mg O catalysts with various amounts of Co content, and the results show that the addition of Mn avoids forming the enclosed catalyst, prevents the formation of amorphous carbon, subsequently promotes the growth of CNTs, and the catalyst with decreased Co content is favorable for the synthesis of CNTs with a narrow diameter distribution.The Co Mn Mg O catalyst with 40% Co content has superior catalytic activity for the growth of carbon nanotubes.