The investigation on the modification of NaY zeolite on LaHY and AEHY (AE refers Ca and Sr and the molar ratio of Ca and Sr is 1:1) zeolites was proformed by XRD, N2-physisorption (BET), XRF, XPS, ...NH3-TPD, Py-IR, hydrothermal stability, and catalytic cracking test. These results indicate that HY zeolite with ultra low content Na can be obtained from NaY zeolite through four exchange four calcination method. The positioning capability of La(3+) in sodalite cage is much better than that of AE(2+) and about 12 La(3+) can be well coordinated in sodalite cages of one unit cell of Y zeolite. Appropriate acid amount and strength favor the formation of propylene and La(3+) is more suitable for the catalytic cracking of cyclohexane than that of AE(2+). Our results not only elaborate the variation of the strong and weak acid sites as well as the Brönsted and Lewis acid sites with the change of exchanged ion content but also explore the influence of hydrothermal aging of LaHY and AEHY zeolites and find the optimum ion exchange content for the most reserved acid sites. At last, the coordination state and stabilization of ion exchanged Y zeolites were discussed in detail.
The well-designed heterostructured CoP/CN/Ni with oriented electron transfer from the inner Ni to the outer CoP shows excellent electrocatalytic hydrogen evolution and oxygen reduction performances.
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•Electronic structure of outer CoP is modulated by the electrons from Ni through CN.•The value of ΔGH* on electron modulated CoP decreases from −0.25 eV to −0.1 eV.•CN layer protects the inner Ni from oxidation and corrosion in harsh environment.•Enriched electrons around CoP weakens its surface oxidation at high potential.
Cobalt phosphide (CoP) with its platinum-group-metal like catalytic features has triggered substantial concerns on electrocatalytic hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) under acidic and alkaline conditions. However, the electrocatalytic rate on CoP is restricted because of the reaction intermediates binding to its surface strongly, leading to sluggish reaction kinetics and unsatisfied catalytic performance. Herein, we describe a ternary heterostructured CoP/CN/Ni catalyst with oriented electron modulation effect to boost its electrocatalytic activity, where the electronic structure of the outer CoP is modulated by the endowed electrons from underlying Ni nanoparticles, which are encapsulated and protected by 2–3 N-doped carbon (CN) layers from oxidation and corrosion in harsh environment. Theoretical calculations reveal that the electron redistribution effect could decrease the adsorption energy of hydrogen (ΔGH*) on CoP from −0.25 eV to −0.1 eV. Benefiting from such electron modulation, CoP/CN/Ni only needs overpotentials of 66 mV in 0.5 M H2SO4 and 106 mV in 1 M KOH for HER to afford a current density of 10 mA cm−2 and presents the comparable ORR activity with Pt/C in 0.1 M KOH. Besides, the unique structure also endows CoP/CN/Ni with superior electrocatalytic stability for HER and ORR.
This work is mainly focused on the investigation of the influence of the amount of a few CeO
2
on the physicochemical and catalytic properties of CeO
2
-doped TiO
2
catalysts for NO reduction by a CO ...model reaction. The obtained samples were characterized by means of XRD, N
2
-physisorption (BET), LRS, UV-vis DRS, XPS, (O
2
, CO, and NO)-TPD, H
2
-TPR,
in situ
FT-IR, and a NO + CO model reaction. These results indicate that a small quantity of CeO
2
doping into the TiO
2
support will cause an obvious change in the properties of the catalyst and the TC-60 : 1 (the TiO
2
/CeO
2
molar ratio is 60 : 1) support exhibits the most extent of lattice expansion, which indicates that the band lengths of Ce-O-Ti are longer than other TC (the solid solution of TiO
2
and CeO
2
) samples, probably contributing to larger structural distortion and disorder, more defects and oxygen vacancies. Copper oxide species supported on TC supports are much easier to be reduced than those supported on the pure TiO
2
and CeO
2
surface-modified TiO
2
supports. Furthermore, the Cu/TC-60 : 1 catalyst shows the highest activity and selectivity due to more oxygen vacancies, higher mobility of surface and lattice oxygen at lower temperature (which contributes to the regeneration of oxygen vacancies, and the best reducing ability), the most content of Cu
+
, and the strongest synergistic effect between Ti
3+
, Ce
3+
and Cu
+
. On the other hand, the CeO
2
doping into TiO
2
promotes the formation of a Cu
+
/Cu
0
redox cycle at high temperatures, which has a crucial effect on N
2
O reduction. Finally, in order to further understand the nature of the catalytic performances of these samples, taking the Cu/TC-60 : 1 catalyst as an example, a possible reaction mechanism is tentatively proposed.
This work is mainly focused on the investigation of the influence of the amount of a few CeO
2
on the physicochemical and catalytic properties of CeO
2
-doped TiO
2
catalysts for NO reduction by a CO model reaction.
A model of intergrowth and coexistence effects of optimized anatase–rutile phases TiO2–SnO2 catalyst which exhibits higher photocatalytic activity than TiO2-P25. Display omitted
•The TiO2–SnO2 ...nanocomposite was synthesized via novel Sol–hydrothermal Technique.•SnO2 adding can accelerate the anatase-to-rutile transformation greatly.•The photocatalytic property was studied upon UV irradiation.•TiO2–SnO2 compounds show superior photocatalytic activity.•The intergrowth and coexistence effects explain excellent photocatalytic activity.
The TiO2–SnO2 nanocomposite with excellent photocatalytic activity was synthesized via sol–hydrothermal process. The obtained samples were characterized by XRD, FETEM, LRS and UV–vis DRS. The photocatalytic activities of as-prepared samples were investigated by degradation of methyl blue (MB) under UV illumination. The results clearly indicate that a small quantity of SnO2 adding can accelerate the anatase-to-rutile transformation greatly, and the nanocomposites consisting of anatase (A) and rutile (R) phases are formed in the molar ratios Ti:Sn=20:1, 60:1 and 80:1, respectively. They show the higher photocatalytic activity than that of TiO2 (A). Remarkably, they can be enhanced up to several times compared with TiO2-P25. Especially, the catalyst of molar ratio Ti:Sn=60:1 is found to be the most efficient, it exhibits a complete decomposition of MB within 20min under UV irradiation. The results are explained by taking into account the intergrowth and coexistence effects of optimized anatase–rutile phases TiO2–SnO2 catalyst, the larger specific surface area and Quantum-sized TiO2–SnO2 particles obtained from the sol–hydrothermal method.
We report here the green oxidation of toluene to benzaldehyde by air under mild conditions in >99% selectivity at 35% conversion at 180 °C. This is an important reaction in both theoretical and ...practical research studies, but little progress has been made in the past five decades. Either the selectivity or the conversion is very low, and the sum of selectivity and conversion is hardly more than one hundred. In previous investigation, we have constructed a highly efficient system of catalysis, i.e., Pickering-like emulsion of toluene in water stabilized by amphiphilic catalysts HDPA-FeO x /Al2O3, hexadecyl phosphonic acid-modulated iron oxides, which work in an enzyme-like mechanism for oxidation of toluene to benzaldehyde. However, the oxygen pressures more than 3 MPa needed for high conversion impede their practical uses. In this work, we modify the catalytic system for the green oxidation of toluene to benzaldehyde using 1 MPa of air as an oxidant. First, the catalytic center of HDPA-FeO x /Al2O3 is optimized as PPA-CuFeO x /Al2O3 with promoted activity of crystal oxygen toward toluene oxidation. Readily available phenylphosphonic acid (PPA), in place of HDPA, shows good performance in the new catalytic system. Second, 5 vol % acetone/water is used as a mixed solvent of the reaction, which markedly modifies the oxygen dissolving and transferring, the access of the toluene molecule to the catalyst, and the recovery rate of catalytic center. The acetone molecule itself, however, is proved not converted and can be recycled in the catalytic process. Comprehensively, the catalytic system including multifactor synergism and good intrinsic safety developed in the current work has realistic feasibility for benzaldehyde production from toluene green oxidation in high-performance and atomic economy.
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•The optimal catalyst with Cu-Nx sites shows efficient ORR performance comparable to Pt/C.•Linear relationships of current and electrochemical active surface areas demonstrated.•The ...Cu-Nx sites are experimentally identified as originates of catalytic ORR.
Carbon catalysts with transition metal atoms anchored via nitrogen coordination have emerged as promising alternatives to Pt in catalyzing oxygen reduction reaction (ORR). However, the intangible evolution of structure in popular synthetic routes containing pyrolysis leads to discrete and irregular M−Nx sites, resulting in limited descriptors and thus ambiguous understandings of structure-activity relationships. We report here a facile method to synthesize Cu-Nx sites of high homogeneity anchored on carbon substrates through deposition and carbonization of glycoluril on metallic copper surface. The Cu-Nx sites take shape under the surface regulation of metallic copper and preferentially exposed after removal of excess Cu. The optimal catalyst presents efficient activity towards ORR with a half-wave potential of 0.84 V (vs. RHE). More importantly, linear relationships over the catalyst between current densities and electrochemical active surface areas (ECSAs) are derived, suggesting activities countable by ECSAs. The correlation clearly demonstrates the high homogeneity and catalytic accessibility of surface-regulated Cu-Nx sites. The well-elucidated structure–activity relationship identifies Cu-Nx sites as originates of catalytic ORR at an experimental level and sheds light on rational engineering of catalysts containing M−Nx sites.
•3D nanospherical CdxZn1−xS/graphene was synthesized via solvothermal method.•Performance evaluation was carried out under visible light irradiation.•Samples show excellent photocatalytic activities ...and photocorrosion resistance.•A possible photocatalytic and anti-corrosion mechanism is proposed.•The structural effects of 3D nanosphere explain excellent performance.
Herein, a series of CdxZn1−xS and sulfide/graphene photocatalysts with 3D nanospherical framework have been successfully fabricated by one-pot solvothermal method for the first time. The morphology and structure of samples were confirmed by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) spectrometry, N2 adsorption, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). The as-prepared samples exhibit excellent photocatalytic activities and photocorrosion resistance in the degradation of dyes under visible light. The Cd0.5Zn0.5S/rGO sample shows the most efficient in the photodegradation of methyl orange (MO). It takes about 30min for degradation completely. The enhanced photocatalytic activity is mainly attributed to the slow photon enhancement of the 3D structure, and the heterojunction between the 3D nanospherical Cd0.5Zn0.5S solid solutions and a high quality 2D rGO support, which can greatly promote the separation of light-induced electrons and holes. Moreover, the large SBET and extended light absorption range also play an important role for improving the photocatalytic activity. The high photocatalytic stability is due to the successful inhibition of the photocorrosion of Cd0.5Zn0.5S/rGO by forming heterojunction between CdS and ZnS, and transferring the photogenerated electrons of Cd0.5Zn0.5S to rGO. The present work can provide rational design of graphene-based photocatalysts with large contact interface and strong interaction between the composites for other application.
The completely selective oxidation of toluene to benzaldehyde with dioxygen, without the need to use H2O2, halogens, or any radical initiators, is a reaction long desired but never previously ...successful. Here, we demonstrate the enzyme-like mechanism of the reaction over hexadecylphosphate acid (HDPA)-bonded nano-oxides, which appear to interact with toluene through specific recognition. The active sites of the catalyst are related to the ability of HDPA to change its bonding to the oxides between monodentate and bidentate during the reaction cycle. This greatly enhances the mobility of the crystal oxygen or the reactivity of the catalyst, specifically in toluene transformations. The catalytic cycle of the catalyst is similar to that of methane monooxygenase. In the presence of catalyst and through O2 oxidation, the conversion of toluene to benzaldehyde is initiated at 70 °C. We envision that this novel mechanism reveals alternatives for an attractive route to design high-performance catalysts with bioinspired structures.
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HDPA-FeMOx/γ-Al2O3 is an enzyme-like catalyst for the exclusive conversion of toluene to benzaldehyde through O2 oxidation under mild conditions.
A series of hexadecylphosphate acid (HDPA) terminated mixed-oxide nanoparticles have been investigated to catalyze the oxidation of toluene exclusive to benzaldehyde under mild conditions in an ...emulsion of toluene/water with the catalysts as stabilizers. With the HDPA-Fe2O3/Al2O3 as the basic catalyst, a series of transition metals, such as Mn, Co, Ni, Cu, Cr, Mo, V, and Ti, was respectively doped to the basic catalyst to modify the performance of the catalytic system, in expectation of influencing the mobility of the lattice oxygen species in the oxide catalysts. Under normally working conditions of the catalytic system, the nanoparticles of catalysts located themselves at the interface between the oil and water phases, constituting the Pickering emulsion. Both the doped iron oxide and its surface adsorbed hexadecylphosphate molecules were essential to the catalytic system for excellent performances with high toluene conversions as well as the exclusive selectivity to benzaldehyde. Under optimal conditions, ∼83% of toluene conversion and >99% selectivity to benzaldehyde were obtained, using molecular oxygen as oxidant and HDPA-(Fe2O3-NiO)/Al2O3 as the catalyst. This process is green and low cost to produce high quality benzaldehyde from O2 oxidation of toluene.
A hexadecylphosphate acid-functionalized (Fe2O3-MOx)/Al2O3 nanorods as the catalyst was used for the oxidation of toluene to benzaldehyde in toluene/water biphasic system under mild conditions. Both the doped iron oxide and the surface adsorbed hexadecylphosphate molecules were essential to provide the excellent catalytic performance for high toluene conversion and the exclusive selectivity to benzaldehyde.
The influence of preparation methods on the physicochemical and photocatalytic activity of Sn4+ doped TiO2 is mainly investigated in this work. Five different preparation methods have been used to ...synthesize SnO2–TiO2 catalysts: sol–gel method (SGM), sol-hydrothermal method (SHM), co-precipitation method (CM), coprecipitation-hydrothermal method (CHM) and hydrothermal method (HM). Their differences in the structures, chemical composition, particle sizes, specific areas, pore size distribution and energy band structure feature were characterized by XRD, XRF, FESEM, LRS, N2-physisorption and UV–vis DRS, respectively. Furthermore, the photocatalytic activity of the as-synthesized products was evaluated by monitoring the degradation of methyl blue (MB) solution under UV illumination. It is shown that the Ti0.75Sn0.25O2 catalyst prepared by the sol-hydrothermal method has the optimum catalytic activity for degradation MB, which is attributed to the optimal crystallization, homogeneous surface, uniform particles, good dispersibility and enhanced light absorption. Moreover, this is a novel method for the synthesis of SnO2–TiO2 photocatalyst firstly combining sol–gel and hydrothermal synthesis. Our findings demonstrate that the new way could be utilized in preparations of other catalysts for promising development of high-performance photocatalysts in the environmental applications.
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