Chaohe Yang

Dual-sized NiFe layered double hydroxides in situ grown on oxygen-decorated self-dispersal nanocarbon as enhanced water oxidation catalysts

The oxygen evolution reaction (OER) is extensively involved in various sustainable energy processes and systems, such as water splitting, fuel cells, and metal–air batteries. Towards superior OER performance, the wise integration of transition metal compounds with nanocarbon materials is a promising strategy. Herein, a mildly oxidized graphene/single-walled carbon nanotube hybrid was introduced to regulate and control the hybridization of nickel–iron layered double hydroxides into a nanocarbon scaffold. The oxygen functionalities and defects anchored the nucleation and in situ growth of dual-sized layered double hydroxides, leading to a hierarchical porous structure for smooth mass diffusion, intimate interfaces for rapid charge transfer, and efficiently utilized active sites. Attributed to the synergy of individual components and the unique structural features, the as-fabricated composites exhibited superior OER performance with a small onset overpotential (ca. 240 mV), a low overpotential required for 10 mA cm−2 (ca. 350 mV), and a decreased Tafel slope (ca. 54 mV dec−1) in 0.10 M KOH. This work provides a brilliant catalyst for water oxidation and more importantly, opens up new avenues for preparing nanocarbon-based multi-functional composites applicable in heterogeneous catalysis, energy conversion and storage, and so on.

Monolithic-structured ternary hydroxides as freestanding bifunctional electrocatalysts for overall water splitting

Efficient oxygen and hydrogen evolution electrocatalysts, based on low-cost and earth-abundant elements, are strongly required for sustainable hydrogen production through water splitting. Herein, we fabricated a monolithic-structured electrode by facilely electrodepositing NiCoFe ternary layered double hydroxides (LDHs) onto 3D conductive scaffolds, providing abundant fully exposed active sites for electrochemical reactions. The moderate Co dopant effectively improved the electrical conductivity of the LDH phase and substantially increased its intrinsic activity. When used for oxygen evolution, the as-obtained monolith LDH electrode exhibited superior kinetics with 275 mV overpotential required to achieve 10 mA cm−2 in 0.10 M KOH, as well as a very low activation energy of 21.0 kJ mol−1. Such a freestanding electrode was also able to catalyze hydrogen evolution efficiently in alkaline media, which further enabled a high-efficiency water electrolyzer delivering 10 mA cm−2 at a very low cell voltage of 1.62 V in 1.0 M KOH. This sheds fresh insight into the principle and process of practical water electrolysis through the rational design of precious-metal-free bifunctional electrodes with a monolithic configuration.

Effects of ammonium exchange and Si/Al ratio on the conversion of methanol to propylene over a novel and large partical size ZSM-5

Abstract One type of ZSM-5 zeolite with large partical size was prepared and characterized by XRD, SEM, N2 adsorption-desorption, XRF, Py-IR and NH3-TPD techniques. Effects of ammonium exchange and SiO2/Al2O3 molar ratios on the reaction of methanol to propylene (MTP) over Na-ZSM-5 and H-ZSM-5 zeolites have been studied in a fixed-bed flow reactor under the operating conditions of T = 500 °C, P = 1 atm, and WHSV = 6 h−1. Ammonium exchange led to a rapid decrease in Na content for Na-ZSM-5 zeolite. The reaction results indicated that Na-ZSM-5 and H-ZSM-5 with different SiO2/Al2O3 molar ratios all exhibited high activity for methanol conversion. Ammonium exchange and the decreased SiO2/Al2O3 molar ratio of ZSM-5 zeolite led to an increase both in strong acid sites and weak acid sites. Na-ZSM-5 with high SiO2/Al2O3 molar ratio was favorable for the formation of propylene. The highest propylene selectivity (45.9%) was obtained over Na-ZSM-5 zeolite catalyst with SiO2/Al2O3 molar ratio of 220.

Hierarchical ZSM-11 with intergrowth structures: Synthesis, characterization and catalytic properties

Abstract Hierarchical ZSM-11 microspheres with intercrystalline mesoporous properties and rod-like crystals intergrowth morphology have been synthesized using a spot of tetrabutylammonium as a single template. XRD, FTIR, SEM, TEM and N2 adsorption analysis revealed that each individual particle was composed of nanosized rod crystals inserting each other and the intercrystalline voids existing among rods gave a significant mesopore size distribution. Steam treatment result demonstrated the excellent hydrothermal stability of samples. Various crystallization modes including constant temperature crystallization (one-stage crystallization) and two-stage temperature-varying crystallization with different 1st stage durations were investigated. The results suggested that the crystallization modes were mainly responsible for the adjustable particle size and textural properties of samples while the small amount of tetrabutylammonium bromide was mainly used to direct the formation of both ZSM-11 framework and its intergrowth morphology. Furthermore, the performance of optimal ZSM-11 as an active component for the catalytic pyrolysis of heavy oil was also investigated. Compared with the commercial pyrolysis catalyst, the hierarchical ZSM-11 catalyst exhibited a high selectivity to desired products (LPG + gasoline + diesel), as well as a much lower dry gas and coke yield, plus a high selectivity and yield of light olefins ( C 3 = - C 4 = ) and very poor selectivity to benzene. Therefore, fully open micropore-mesopore connectivity would make such hierarchically porous ZSM-11 zeolites very attractive for applications in clean petrochemical catalysis field.

Effects of temperature and catalyst to oil weight ratio on the catalytic conversion of heavy oil to propylene using ZSM-5 and USY catalysts

Abstract It is useful for practical operation to study the rules of production of propylene by the catalytic conversion of heavy oil in FCC (fluid catalytic cracking). The effects of temperature and C/O ratio (catalyst to oil weight ratio) on the distribution of the product and the yield of propylene were investigated on a micro reactor unit with two model catalysts, namely ZSM-5/Al2O3 and USY/Al2O3, and Fushun vacuum gas oil (VGO) was used as the feedstock. The conversion of heavy oil over ZSM-5 catalyst can be comparable to that of USY catalyst at high temperature and high C/O ratio. The rate of conversion of heavy oil using the ZSM-5 equilibrium catalyst is lower compared with the USY equilibrium catalyst under the general FCC conditions and this can be attributed to the poor steam ability of the ZSM-5 equilibrium catalyst. The difference in pore topologies of USY and ZSM-5 is the reason why the principal products for the above two catalysts is different, namely gasoline and liquid petroleum gas (LPG), repspectively. So the LPG selectivity, especially the propylene selectivity, may decline if USY is added into the FCC catalyst for maximizing the production of propylene. Increasing the C/O ratio is the most economical method for the increase of LPG yield than the increase of the temperature of the two model catalysts, because the loss of light oil is less in the former case. There is an inverse correlation between HTC (hydrogen transfer coefficient) and the yield of propylene, and restricting the hydrogen transfer reaction is the more important measure in increasing the yield of propylene of the ZSM-5 catalyst. The ethylene yield of ZSM-5/Al2O3 is higher, but the gaseous side products with low value are not enhanced when ZSM-5 catalyst is used. Moreover, for LPG and the end products, dry gas and coke, their ranges of reaction conditions to which their yields are dependent are different, and that of end products is more severe than that of LPG. So it is clear that maximizing LPG and propylene and restricting dry gas and coke can be both achieved via increasing the severity of reaction conditions among the range of reaction conditions which LPG yield is sensitive to.

Synthesis of a ZSM-5(core)/SAPO-5(shell) composite and its application in FCC

A core/shell structure composite was synthesized via a new method of pre-coating one raw material. The composite was characterized by X-ray diffraction, SEM, TEM and N2 isothermal adsorption–desorption and Py-FTIR. In addition, the catalytic performance of the composite in cracking of heavy oil for producing olefin was also investigated. The characterization results show that the composite with a core/shell structure had smaller particle size, uniform SAPO-5 shell, and fewer acid sites than ZSM-5, accelerating the transport of reactant and product molecules between different zeolites. Consequently, the light olefins on the composites had high specific selectivity.

Effect of acid density of HZSM-5 on the oligomerization of ethylene in FCC dry gas

Abstract The oligomerization of ethylene in FCC dry gas over HZSM-5 catalyst with different Si/Al 2 ratios was studied. The effect of acid density of catalyst on the oligomerization of ethylene was discussed. By increasing the acid density of catalyst, ethylene conversion showed a linear increase, while the yields of olefins decreased when the acid density of catalyst exceeded 0.14 mmol NH3 /g owing to a promotion of hydrogen transfer reaction. Through comparing the average distance between acid sites on catalyst with kinetic diameters of olefins, it was found that the dimerization of ethylene was not restrained by the sparse distribution of acid sites, while the hydrogen transfer reaction of C 3 and C 4 olefins was limited. On these bases, a conclusion is proposed that the dimerization of ethylene proceeded via Eley-Rideal mechanism, while the hydrogen transfer reaction of C 3 and C 4 olefins followed the Langmuir-Hinshelwood mechanism.

A high-surface-area silicoaluminophosphate material rich in Brönsted acid sites as a matrix in catalytic cracking

A transparent gel-like mesoporous silicoaluminophosphate material (SAP) with a Si/Al molar ratio of 20 was synthesized by hydrothermal method. The physicochemical features of SAP were characterized by XRD, XRF, BET, SEM and FT-IR spectroscopy of pyridine adsorption techniques. The results indicated that incorporation of phosphorus (P) into aluminasilica system altered the basic textural characteristics of aluminasilica. Especially after hydrothermal treatment, the material with large special surface area (up to 492 m2/g) exhibited a good performance on hydrothermal stability. Moreover, the phosphorus modifier can not only increase the amount of Bronsted acidic sites (up to 48.44 μmol/g) and the percentage of weak acidic sites in total acidic sites, but also regulate the acid type, such as the ratio of B/L (Bronsted acid/Lewis acid) increases to 1.15. The performances of samples as matrices for the catalytic cracking of heavy vacuum gas oil (VGO) were investigated. At 520 °C, the catalysts showed much higher gasoline and diesel oil yields achieving to 45.59 wt% and 19.20 wt%, respectively, and lower coke selectivity (2.86%) than conventional FCC matrices, such as kaolin and amorphous silica-alumina.

Preparation and characterization of Mn/MgAlFe as transfer catalyst for SOx abatement

Abstract A series of manganese-promoted MgAlFe mixed oxides, used as sulfur transfer catalysts, were prepared by acid-processed gelatin method and characterized by TGA-DTA, XRD, N 2 adsorption-desorption and FT-IR techniques. It was found that the sulfur transfer catalysts with 0.5–3.0 wt% manganese showed its good dispersion in the precursor. The novel Mn/MgAlFe catalysts with 0.5–5.0 wt% manganese oxide showed a high oxidative adsorption rate and sulfur adsorption capacity, and 5.0 wt% Mn/MgAlFe sample was superior to the others for SO 2 removal. Moreover, the presence of CO had no obvious effect on the adsorption activity of sulfur transfer catalysts for SO 2 uptake.

Synergistic effect of W and P on ZSM-5 and its catalytic performance in the cracking of heavy oil

In order to develop the conversion of heavy oil with a high yield of propylene in the catalytic cracking process, ZSM-5 zeolite was modified by tungsten and phosphorus, which was proved to be an effective method. Characterization results show that the improvement of catalytic performance could be correlated to the interaction of phosphorus and tungsten species on ZSM-5. P inhibited the aggregation of tungsten species on ZSM-5 and was conductive to convert the tungsten species with octahedral coordination into tetrahedral coordination. And this ultimately led to that more acid sites were reserved after hydrothermal treatment in the tungsten and phosphorus co-modified ZSM-5 catalyst. Phosphorus species played an important role to restrain the dehydrogenation activity of tungsten. In addition, a model reflecting the interaction between tungsten species and ZSM-5 framework was proposed.