TiO2-containing bulk Ni2P catalysts (Tix-Ni2P) were prepared by coprecipitation and in situ H2 temperature-programmed reduction (TPR), and characterized by XRD, CO chemisorption, TEM, XPS, TPR, and NH3-TPD. Their hydrodenitrogenation performances were studied by using quinoline and decahydroquinoline (DHQ) as the model molecules. Both the hydrogenation and C−N bond cleavage activities of Ni2P were improved by the introduction of TiO2. The TiO2 species were mainly located separately on the surface of the catalysts and had strong interactions with surface Ni and P species. The reducibility of the precursors as well as the surface electronic properties of Ni2P catalysts were affected by the addition of TiO2. Tix-Ni2P showed higher CO uptake but less acid sites than Ni2P. The promoting effect of TiO2 was discussed by considering the electronic interactions between surface Ti and Ni2P species and changes in the adsorption geometries of quinoline, DHQ, as well as the partially hydrogenated intermediates over Tix-Ni2P.

•The actual active surface of the bulk WP catalyst is a sulfur-containing phase.•The formation of the tungsten phosphosulfide phase is fast.•The presence of sulfur decreases the electron densities of the surface WP species.•Strong adsorption of NH3 (formed by the hydrodenitrogenation of piperidine) on WP.•NH3 is a strong poison for the metal phosphide hydrodesulfurization catalysts.The X-ray photoelectron spectroscopy characterization of a bulk WP hydrodesulfurization (HDS) catalyst demonstrated that the actual active surface phase of WP in the HDS of dibenzothiophene (DBT) is a sulfur-containing phase. This tungsten phosphosulfide phase formed faster than the molybdenum phosphosulfide phase, but possessed a lower sulfur content than the corresponding Ni2P and MoP phases. NH3 was the dominant nitrogen-containing species detected in the WP catalyst after simultaneous HDS and hydrodenitrogenation reactions. NH3 decreased the DBT conversion strongly but less than piperidine, indicating that not only N-containing compounds but also NH3 inhibits the HDS activity of WP.Download high-res image (60KB)Download full-size image

The XPS, XANES, and UV–Vis results revealed that oxygen vacancies were formed in the surface of MoO3/SiO2 by impregnation of the catalyst with citric acid followed by a temperature-programmed heating under N2 atmosphere. The presence of the induction period during the oxidative desulfurization (ODS) of dibenzothiophene over these Mo-based catalysts using cumene hydroperoxide as the oxidant suggests that the reaction would follow a free radical mechanism. Both the higher ODS activity and the faster deactivation of the modified catalysts give evidences that the oxygen vacancies should possess a high ODS activity.

•The steric hindrance mainly suppressed the reactivities of S-compounds and olefins.•H2S inhibition effect was severe on HDS reactivity, thus decreasing the selectivity.•The interconversion of Lewis and Brønsted acid sites explained the H2S inhibition.•The HYD pathway of the HDS reaction was principally affected.•Catalysts with appropriate acidic sites proportion was effective in selective HDS.The reactivity of different groups of olefins and S-compounds, as well as the inhibition effect of H2S on the reactivities of these groups were evaluated with a FCC gasoline over a CoMoS/γ-Al2O3 catalyst. The results demonstrated that the various degrees of steric hindrance around the double bond (CC) and of the thiophene molecules suppressed the hydrogenation (HYD) of olefins and hydrodesulfurization (HDS) of S-compounds, respectively. The inhibition effect of H2S caused by the easy adsorption of H2S on the catalyst sites was more severe on the HDS reactivity than that on the olefins HYD reactivity, thus leading to the decreased catalyst selectivity. The inhibition effect of H2S increased with the number of substituents to the olefin double bond and to the number of substituents to the thiophene molecules, which was inversely proportional to the adsorption constants of the olefin and thiophene molecules. Meanwhile, a modification of the HDS reaction pathway of thiophenes induced by H2S was also observed, and the HYD pathway was more depressed. The characterization by Fourier transformed infrared spectroscopy showed that the relative variations of the number of Lewis and Brønsted acid sites induced by the adsorbed H2S could explain the H2S effect.Graphical abstract

The decomposition of hydrogen sulfide (H2S) has attracted increasing attention because it produces hydrogen from a hazardous waste gas. However, the thermal equilibrium limitation in the decomposition gives rise to low H2S conversion and high energy costs for hydrogen production. In the present work, we demonstrate that alumina-supported CdS and ZnS significantly enhanced the conversion in the non-thermal plasma-induced decomposition of H2S, achieving full conversion at reasonably low energy consumption. It appears that the enhancement might be attributed to the conversion of H2S by its reaction with h+ and e− on the surface of the CdS and ZnS semiconductors, which are generated by the strong electric field and plasma-induced photons.

Three series of aluminosilicate MCM-41 (Al-MCM-41) were synthesized using different aluminum sources, including aluminum isopropoxide (AlM-I), pseudoboehmite, and aluminum sulfate, by a hydrothermal method. The hydrodesulfurization (HDS) performance of the Al-MCM-41-supported Pd and Pt catalysts prepared with chlorided precursors were evaluated with dibenzothiophene (DBT) as the model sulfur-containing molecule, in comparison with those supported on a siliceous MCM-41 (SiM). Pd/SiM and Pt/SiM were not promising for DBT HDS because of their relatively low activities and the rapid irreversible deactivation. Pd and Pt supported on the acidic Al-MCM-41 materials showed higher dispersion and enhanced HDS performances. AlM-I, which possessed the strongest acidity, was the most promising among the mesoporous materials investigated. The deactivated Pd/AlM-I and Pt/AlM-I can be reversibly regenerated by H2 reduction. DBT HDS over the Pd catalysts predominantly took the hydrogenation (HYD) pathway, whereas the direct desulfurization (DDS) pathway and HYD pathway were comparable for the Pt catalysts. Increasing the support acidity had no positive effect on the DDS activity of Pd but significantly enhanced its HYD activity, while the increase in the rate constant of DDS pathway was close to that of the HYD pathway for Al-MCM-41-supported Pt catalysts. The effect of the acid properties of the supports on the HDS performance of Pd and Pt catalysts was discussed by considering the formation of “electronic-deficient” particles and the hydrogen spillover process.

Nickel phosphate nanotubes (NiPO-NTs) were obtained via a simple urea-assisted hydrothermal route in the absence of organic surfactant as the structure-directing agent. The material possessed an urchin-shaped structure, and the one dimensional nanotubes were directed outward around the spheres. SEM and TEM observations indicated that the NiPO-NTs had an outer diameter of about 7.0 nm, inner diameter of 4.0 nm, and length of around 0.75 μm. It is found that the formation of NiPO-NTs was determined by the pH value and its changing rate, which were controlled by urea hydrolysis. Accordingly, a possible mechanism of nanotube formation was proposed. The synthesized NiPO-NTs showed high catalytic performance in the epoxidation of cyclohexene.Highlights► Nickel phosphate nanotubes were obtained in the absence of organic templates. ► The formation of nanotubes results from the controlled thermal decomposition of urea. ► The synthesized nanotubes showed high catalytic performance in epoxidation of cyclohexene.

Bulk Ni2P and CeO2-containing bulk Ni2P (Ce–Ni2P(x), where x represents the Ce/Ni atomic ratio) were prepared by a co-precipitation method followed by an in situ H2 temperature-programmed reduction procedure. The catalysts were characterized by XRD, CO chemisorption, TEM, N2 adsorption–desorption, XPS and X-ray absorption spectroscopy (XAS). Their hydrodenitrogenation performances were studied using quinoline (Q) and decahydroquinoline as the model compounds. Both the hydrogenation and C–N bond cleavage activities of Ni2P were improved by the introduction of CeO2. CeO2 mainly accelerated the denitrogenation of Q to propylcyclohexane rather than to propylbenzene. XRD and XPS measurements revealed that the Ce species in Ce–Ni2P(x) were mainly in the oxide form and both Ce4+ and Ce3+ species coexisted on the surface of the catalysts. Addition of CeO2 significantly decreased the particle size of Ni2P, resulting in increased specific surface areas and CO uptakes, possibly due to the strong interaction between the Ce species and Ni2P. At a Ce/Ni atomic ratio higher than 0.25, segregation of CeO2 took place. XAS results of the passivated catalysts showed that CeO2 not only affected the oxidability of Ni2P but also led to the formation of metallic Ni. The promoting effect of CeO2 was discussed by considering the electronic interactions between Ce species and Ni2P as well as the presence of the amorphous Ni and low valence Ce3+ species.

A bulk Ni2P catalyst was prepared by co-precipitation of nickel phosphate followed by in situ temperature-programmed reduction (TPR) with H2. The hydrodesulfurization (HDS) of dibenzothiophene (DBT) and its hydrogenated intermediates 1,2,3,4-tetrahydro-dibenzothiophene (TH-DBT) and 1,2,3,4,4a,9b-hexahydro-dibenzothiophene (HH-DBT) was studied at 340 °C and 4 MPa both in the presence and absence of piperidine (Pi). Bulk Ni2P exhibited a relatively low hydrogenation/dehydrogenation activity but high desulfurization activity. Pi retarded the hydrogenation of DBT to a greater extent than the desulfurization. The desulfurization of HH-DBT to 2-cyclohexen-1-yl-benzene (CHEB-2) occurred mainly by β-elimination of the hydrogen atom attached to carbon atom C(4), whereas TH-DBT desulfurized mainly by hydrogenolysis to 1-cyclohexen-1-yl-benzene (CHEB-1). A minor amount of biphenyl (BP) observed in the HDS of TH-DBT and HH-DBT is due to the disproportionation of cyclohexenyl-benzenes. A reaction network of the HDS of DBT over Ni2P is postulated in which both β-elimination and hydrogenolysis play a role in the breaking of the C–S bonds.

Mesoporous aluminosilicates (YM) were hydrothermally synthesized by assembling zeolite subunits, which were generated by the hydrolysis of HY zeolite in Na2SiO3 aqueous solution, in the presence of cetyltrimethylammonium bromide (CTAB). The Na2SiO3 aqueous solution plays two roles in the synthesis. It provides a moderate alkaline medium with buffering effect for the desilication of HY zeolite and it acts as a supplementary silica source. The desilication of HY zeolite was optimized in terms of reaction temperature and time. Characterizations by XRD, nitrogen isotherms and TEM indicated that YM possessed a well-ordered mesostructure. FT-IR, UV-Raman, 27Al MAS NMR, NH3-TPD, and pyridine-adsorbed IR showed that the characteristics of Y zeolite, such as double six-membered ring subunits, tetrahedral coordination aluminum and high ratio of Brönsted/Lewis acidity sites, were preserved in YM. SEM observation revealed YM possesed a different morphology from either mesoporous MCM-41 or Y zeolite. No separate zeolite crystals were found in the TEM observation. The hydrothermal stability of YM towards refluxed water (120 h) and steam (873 K, 6 h), and the activity in acid-catalyzed cumene cracking (623 K) were compared with MCM-41 prepared with conventional method or parent HY. Because of the uniform structure and surface properties, YM was more hydrothermally stable than MCM-41; it also exhibited more efficient catalytic activitation than MCM-41 and HY in cumene cracking.

Ultrafine nitrogen-doped TiO2 nanoparticles with narrow particle size distribution, good dispersion, and high surface area were synthesized in the presence of urea and PEG-4000 via a hydrothermal procedure. TEM observation, N2 adsorption, XRD, UV–vis spectroscopy, the Raman spectroscopy and XPS analysis were conducted to characterize the synthesized TiO2 particles. The synthesized TiO2 particles were a mixture of 49.5% anatase and 50.5% rutile with a size of around 5 nm. The photocatalytic activities were tested in the degradation of an aqueous solution of a reactive Brilliant Blue KN-R under both UV and visible light. The synthesized TiO2 particles showed much higher photocatalytic activity than a commercial P25 TiO2 powder under both UV and visible light irradiations. The high performance is associated to N doping, the reduced particle size, good dispersion, high surface area, and a quantum size effect.

Overgrowth of MCM-41 on HY zeolite was performed using different templates [cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium chloride (CTACl)]. The hydrodesulfurization (HDS) performances of Ni−Mo sulfides supported over these synthesized composites were evaluated with dibenzothiophene (DBT) as the model sulfur-containing molecule. TEM and STEM images revealed that zeolite HY overgrown with an MCM-41 layer (less than 20 nm) was obtained using CTABr as the template [MY(Br)], and the MCM-41 pore channels were assumed to be oriented outward from the inner HY core. Nevertheless, for the samples synthesized using CTACl [MY(Cl)], the HY crystals were buried independently in the MCM-41 phase. Both Ni−Mo/MY(Br) and Ni−Mo/MY(Cl) showed higher HDS activity and reducibility than Ni−Mo/MCM-41. The hydrogenation activity of Ni−Mo/MCM-41 was enhanced more than the direct desulfurization activity by the introduction of HY zeolite. Ni−Mo/MY(Br) and Ni−Mo/MY(Cl) exhibited hydrocracking activities equivalent to that of Ni−Mo/MCM-41, indicating that the HDS of DBT predominantly takes place in the mesopores of Ni−Mo/MY(Br) and Ni−Mo/MY(Cl). Because the active species located in the mesopores cannot have close contact with the strong acid sites of the HY zeolite, it is suggested that the spillover hydrogen might play an essential role in the HDS reaction over the supported Ni−Mo sulfides.

A series of transition metal phosphides, including MoP, WP, CoP, Co2P, and Ni2P, were synthesized from their oxidic precursors by means of hydrogen plasma reduction under mild conditions. The effects of reduction conditions, such as metal to phosphorus molar ratio, power input, and reduction time, on the synthesis of metal phosphides were investigated. The products were identified by means of XRD characterization. It is indicated that metal phosphides were readily synthesized stoichiometrically from their oxides in hydrogen plasma under mild conditions.Metal phosphides were obtained stoichiometrically from their oxidic precursors by hydrogen plasma reaction under mild conditions.

Two novel mesoporous nickel phosphates (NiPO-1 and NiPO-2) with nanotubular structures were developed in the presence of cationic surfactant and different bases by a sol–gel method. The mesostructures of NiPO-1 and NiPO-2 are composed of nanotubes of different lengths, which are arranged by a less-ordered lamellar symmetry as synthesized. ICP elemental analysis revealed that they are different compounds. The Ni/P molar ratios of NiPO-1 and NiPO-2 are 1.57 and 1.20, respectively. Both materials possess a relatively high BET surface area (205–292 m2 g−1) and good thermal stability up to 673 K. It is found that these novel materials exhibited high activity (>50%) and high selectivity to epoxide (95.6% and 99.0%) in the epoxidation of cyclododecene with H2O2 as oxidant.

A three-stage temperature-programmed (TP) calcination route to remove the templates from hexagonal mesoporous aluminophosphates (meso-AlPO) was developed. XRD results showed that the condensation and order degrees of inorganic framework of meso-AlPO calcined by this TP route were greatly increased, which is much better than the conventional method. It was also found that the shrinkage of the pore structure decreased and further the pore size of the product became larger than the previous report. This shows a novel calcination route to improve highly ordered mesostructures and the thermal stability of the meso-AlPO materials.

A hybrid material ([Bmim]3PMo12O40) was synthesized by reacting H3PMo12O40 with the ionic liquid 1-butyl-3-methyl imidazolium bromide. SiO2-supported [Bmim]3PMo12O40 showed a high catalytic activity in the oxidation of dibenzothiophene (DBT) with 29% H2O2 aqueous solution as the oxidant. Maximum activity was observed at a loading of 20 wt.% [Bmim]3PMo12O40 on SiO2, and 100% DBT conversion was achieved at 60 °C, atmospheric pressure, and an oxygen to sulfur (O/S) molar ratio of 3.0 in 100 min. The high performance of [Bmim]3PMo12O40/SiO2 might be attributable to its amphiphilicity, which enhances adsorption of both H2O2 and sulfur-containing compounds. [Bmim]3PMo12O40/SiO2 could be easily separated by centrifugation and reused without deactivation after seven runs. Quinoline and carbazole had slightly positive effects on DBT oxidation, whereas indole had a negative effect. The high performance of [Bmim]3PMo12O40 was verified in the sulfur removal from a real diesel by means of oxidation followed by dimethylformamide extraction.Graphical abstract[Bmim]3PMo12O40/SiO2, which is amphiphilic, exhibits high catalytic performance in the oxidation of dibenzothiophene and a real diesel. Quinoline and carbazole show slight promoting effects, whereas indole strongly inhibits the oxidation.Download high-res image (73KB)Download full-size imageResearch highlights► [Bmim]3PMo12O40/SiO2 is an outstanding catalyst in oxidative desulfurization. ► The aqueous phase adsorbs on catalyst particles, which work like microreactors. ► The aqueous phase and solid catalyst are separated simultaneously from oil phase. ► The dried spent catalyst was reused for seven runs without deactivation. ► Nitrogen compounds may have positive or negative effects.

The effect of TiO2 on the hydrodenitrogenation (HDN) performance of MoP/MCM-41 was investigated using quinoline and decahydroquinoline as the model molecules. The catalysts were characterized by XRD, CO chemisorption, TEM, TPR and pyridine FT-IR. Addition of TiO2 enhanced the C–N bond cleavage activity of MoP/MCM-41 but inhibited its dehydrogenation activity. A maximum HDN activity was observed when the TiO2 loading was 5 wt%. The characterization results indicated that introduction of TiO2 did not affect the formation of MoP phase. The TiO2-containing catalysts possessed higher CO uptake than MoP/MCM-41, but no significant differences in the acid properties and particle size distributions were observed for all the catalysts. XPS results revealed a surface enrichment of TiO2 in Ti-containing catalysts and small amount of these surface TiO2 can be partially reduced to Tin+ (n < 4). It is suggested that these Tin+ (n < 4) species may be responsible for the promoting effect of TiO2 on the HDN performance of MoP/MCM-41.

Catalytic oxidation of dibenzothiophene (DBT) in decalin was performed using an oil-soluble oxidant, cumene hydroperoxide (CHP), over molybdenum oxide (MoO3) supported on silica. The effects of MoO3 loading, reaction time and the molar ratio of CHP/DBT were investigated. At a MoO3 loading of 15 wt%, the conversion of DBT reached 82% at 70 °C, WHSV 30 h−1, and O/S molar ratio 3. Alkaline earth metals, such as Ca, Ba, Sr and Mg were introduced on the surface of silica, prior to the impregnation of MoO3. The results showed that the activity in the oxidation of DBT with CHP decreased in the order: MoO3/Ca-SiO2 > MoO3/Ba-SiO2 > MoO3/SiO2 > MoO3/Sr-SiO2 > MoO3/Mg-SiO2. The MoO3/Ca-SiO2 catalysts were characterized by XRD. The DBT conversions on MoO3/Ca-SiO2 catalysts with various Ca/Mo ratios were studied. When the Ca/Mo ratio was 0.05, the DBT conversion was the highest (95%) at 60 °C, WHSV 30 h−1, and O/S molar ratio 3.0.

•The CoMo/γ-Al2O3 catalysts sulfided in H2S/N2 showed much high selectivity.•Sulfidation of active components in H2S/N2 was more completed than that in H2S/H2.•The catalytic performance was mainly determined by the first sulfidation atmosphere.•The MoS2 morphology differences could better explain the HDS selectivity.•Controlling the slab lengths of supported MoS2 could regulate its HDS selectivity.The effect of sulfidation atmosphere (H2S/H2 and H2S/N2) on the morphology of (Co)MoS2 particles supported on γ-Al2O3 was studied and the prepared catalysts were evaluated in selective hydrodesulfurization (HDS) of FCC gasoline. It was found that the selectivity of the CoMo/γ-Al2O3 catalysts sulfided in H2S/N2 was 1.8 times as high as that sulfided in H2S/H2, and the catalytic performance was mainly determined by the first sulfidation atmosphere after the impregnation of Mo. The characterization by XRD, HRTEM, XPS, TPR and FT-IR showed that the more completed sulfidation of Mo oxides in H2S/N2 could effectively weaken the strong interaction between the γ-Al2O3 support and active components, thus inducing the decisive influence on the morphology of MoS2 particles. The MoS2 morphology differences could better explain the HDS selectivity. The CoMo/γ-Al2O3 catalyst sulfided in H2S/N2 showed significantly longer slab lengths of supported MoS2 slabs, which effectively decreased the number of active adsorption sites for olefins and thus suppressed the hydrogenation activity of olefins, leading to a desirable higher HDS selectivity. Therefore, a tailor-made catalyst with high HDS selectivity could be developed by optimally controlling the slab lengths of supported MoS2 slabs.Download high-res image (221KB)Download full-size image

Mesoporous aluminosilicates (YM) were hydrothermally synthesized by assembling zeolite subunits, which were generated by the hydrolysis of HY zeolite in Na2SiO3 aqueous solution, in the presence of cetyltrimethylammonium bromide (CTAB). The Na2SiO3 aqueous solution plays two roles in the synthesis. It provides a moderate alkaline medium with buffering effect for the desilication of HY zeolite and it acts as a supplementary silica source. The desilication of HY zeolite was optimized in terms of reaction temperature and time. Characterizations by XRD, nitrogen isotherms and TEM indicated that YM possessed a well-ordered mesostructure. FT-IR, UV-Raman, 27Al MAS NMR, NH3-TPD, and pyridine-adsorbed IR showed that the characteristics of Y zeolite, such as double six-membered ring subunits, tetrahedral coordination aluminum and high ratio of Brönsted/Lewis acidity sites, were preserved in YM. SEM observation revealed YM possesed a different morphology from either mesoporous MCM-41 or Y zeolite. No separate zeolite crystals were found in the TEM observation. The hydrothermal stability of YM towards refluxed water (120 h) and steam (873 K, 6 h), and the activity in acid-catalyzed cumene cracking (623 K) were compared with MCM-41 prepared with conventional method or parent HY. Because of the uniform structure and surface properties, YM was more hydrothermally stable than MCM-41; it also exhibited more efficient catalytic activitation than MCM-41 and HY in cumene cracking.

Two novel mesoporous nickel phosphates (NiPO-1 and NiPO-2) with nanotubular structures were developed in the presence of cationic surfactant and different bases by a sol–gel method. The mesostructures of NiPO-1 and NiPO-2 are composed of nanotubes of different lengths, which are arranged by a less-ordered lamellar symmetry as synthesized. ICP elemental analysis revealed that they are different compounds. The Ni/P molar ratios of NiPO-1 and NiPO-2 are 1.57 and 1.20, respectively. Both materials possess a relatively high BET surface area (205–292 m2 g−1) and good thermal stability up to 673 K. It is found that these novel materials exhibited high activity (>50%) and high selectivity to epoxide (95.6% and 99.0%) in the epoxidation of cyclododecene with H2O2 as oxidant.