Hydrodechlorination of Chlorobenzene over Silica-Supported Nickel Phosphide Catalysts

Transition Metal Phosphide Nanoarchitectonics for Versatile Organic Catalysis

Transition metal phosphides (TMP) posses unique physiochemical, geometrical, and electronic properties, which can be exploited for different catalytic applications, such as photocatalysis, electrocatalysis, organic catalysis, etc. Among others, the use of TMP for organic catalysis is less explored and still facing many complex challenges, which necessitate the development of sustainable catalytic reaction protocols demonstrating high selectivity and yield of the desired molecules of high significance. In this regard, the controlled synthesis of TMP-based catalysts and thorough investigations of underlying reaction mechanisms can provide deeper insights toward practical achievement of desired applications. This review aims at providing a comprehensive analysis on the recent advancements in the synthetic strategies for the tailored and tunable engineering of structural, geometrical, and electronic properties of TMP. In addition, their unprecedented catalytic potential toward different organic transformation reactions is succinctly summarized and critically analyzed. Finally, a rational perspective on future opportunities and challenges in the emerging field of organic catalysis is provided. On the account of the recent achievements accomplished in organic synthesis using TMP, it is highly anticipated that the use of TMP combined with advanced innovative technologies and methodologies can pave the way toward large scale realization of organic catalysis.

Synthesis of Pd-CoxOy Hybrid Nanostructure-Encapsulated Hollow Silica Nanospheres through Reverse Microemulsion Systems and Their Application as Efficient Hydrodechlorination Catalysts

Pd-Co_xO_y heteroaggregate-encapsulated hollow porous silica nanoreactors (Pd-Co_xO_y@HPSNs) were synthesized by a reverse microemulsion system. The key design of the developed reverse microemulsion system is to use poly(ethyleneimine) in the water droplets as the void templates for silica deposition and for anchoring the catalytic functionality inside the hollow silica nanospheres. The synthesized Pd-Co_xO_y@HPSNs contain ∼3 nm Pd-Co_xO_y hybrid nanostructures in ∼10 nm central cavities of silica nanospheres and illustrated a significantly promoted efficiency for hydrodechlorination of a series of chlorophenols into phenols under mild reaction conditions. The catalytic enhancement of Pd-Co_xO_y@HPSNs is ascribed to the synergistic effect between Pd and Co_xO_y and the protection of silica shells to the inner catalytic functionality.

Promoting Effects of Al on Ni-Based Catalyst for the Hydrodeoxygenation Performance of Ethyl Acetate

The mesoporous Ni20/Al-KIT-6 (denoted as N20AxK) catalysts with different Al content (1–9 wt%) were prepared, metal Ni and KIT-6 modified by Al were used as active component and support, respectively. The physicochemical properties of the prepared N20AxK catalysts were characterized by H2-TPR, XRD, BET, TEM, and H2-TPD. The catalytic hydrodeoxygenation(HDO) performance of N20AxK catalysts was evaluated by ethyl acetate catalytic HDO. The results show that the catalytic HDO performance of the prepared N20AxK catalysts is related to the adsorption and activation performance for H2 molecules, as well as the dispersion of matal Ni active components. N20A5K catalyst shows the best H2 adsorption property and Ni dispersion. N20A5K catalyst presents superior catalytic HDO performance. At 300 °C and atmospheric pressure, the conversion of ethyl acetate and ethane selectivity of N20A5K catalyst are 99.3 % and 97.4 %, respectively. Besides, the N20A5K catalyst exhibits good stability.

Metal-support interactions in the design of heterogeneous catalysts for redox processes

The effect of the metal-support interaction (MSI) has been discussed for several types of catalytic systems comprising metal nanoparticles (Ni, Pd, Au, Fe) on oxide and carbon supports, showing promising catalytic properties in hydrogenation of unsaturated C–C bonds, hydrodechlorination (HDC) of chlorinated organic molecules and CO total oxidation. The MSI of a different strength, from the redistribution of the electron density of nanoparticles (NPs) to the chemical interactions, is determined by the composition of the support and the active site, the method of active metal deposition, calcination temperature, particle size etc. The types of MSI considered in this review include: (1) the interaction of the active metal (Me) NPs with alumina and modified zirconia to form several oxidation states of Me in the composition of surface or bulk chemical compounds with a support; (2) the influence of oxide (alumina, silica) or carbon (highly oriented pyrolytic graphite, Sibunit) supports on the formation of active sites in the catalysts with ultra-low Me loading prepared by deposition of pre-formed metal NPs produced by laser electrodispersion (LED) or as colloidal dispersion; (3) the anchoring of Me NPs on the surface of carbon supports (nanodiamonds and carbon nanotubes) directly with a support surface, e.g. through surface defects, or through surface functional groups; (4) ‘reverse’ MSI in the Me@C composites, consisting of metal NPs, covered with the defected graphene layers or immersed into carbon matrix. It is demonstrated on the example of LED systems, that oxidation of metal under MSI is less significant in carbon-supported systems than in oxide-supported ones, but charge effects can play a noticeable role for both types of supports. Different ways of MSI tuning provide the possibilities to achieve the optimal Men+/Me0 ratio in the catalysts for HDC of mono- and polychlorinated organic molecules, including persistent organic pollutants. One of these ways is tuning the composition of functional groups on the surface of nanodiamonds and carbon nanotubes by additional treatments to achieve the desirable metal anchoring, the optimal metal NPs size and the improved catalytic properties. Unusual type of MSI is represented by the activation of thin graphene shell of Me@C composites by the presence of defects in the shell and a transition metal (Ni, Fe) in subsurface layer. This effect allows H2 activation that is a significant step in many industrially important reactions. The selectivity and activity of such systems can be intentionally changed by varying the nature of metal and reaction temperature. Significant attention has been given in the review to the novel catalytic systems described in the previous works of the authors.

General Strategy for Controlled Synthesis of NixPy/Carbon and Its Evaluation as a Counter Electrode Material in Dye-Sensitized Solar Cells

Hydrothermal treatment of nickel acetate and phosphoric acid aqueous solution followed with a carbothermal reduction assisted phosphorization process using sucrose as the carbon source for the controlled synthesis of Ni_xP_y/C was successfully realized for the first time. The critical synthesis factors, including reduction temperature, phosphorus/nickel ratio, pH, and sucrose amount were systematically investigated. Remarkably, the carbon serves as a reducer and plays a determinative role in the transformation of Ni₂P₂O₇ into Ni₂P/C. The synthesis strategy is divided into four distinguishable stages: (1) hydrothermal preparation of Ni₃(PO₄)₂·8H₂O precursor for stabilizing P sources; (2) dimerization of Ni₃(PO₄)₂·8H₂O into more thermal stable Ni₂P₂O₇ amorphous phase along with the generation of NiO; (3) carbothermal reduction and phosphidation of NiO into Ni_xP_y (0 ≤ y/x ≤ 0.5); and (4) further phosphidation of mixed-phase Ni_xP_y and carbothermal reduction of Ni₂P₂O₇ into single-phase Ni₂P. The resultant Ni₂P, the highly active phase in electrocatalysis, was applied as counter electrode in a dye-sensitized solar cell (DSSC). The DSSC based on Ni₂P with 10.4 wt.% carbon delivers a power conversion efficiency of 9.57%, superior to that of state-of-the-art Pt-based cell (8.12%). The abundant Ni^δ+ and P^δ- active sites and the metal-like conductivity account for its outstanding catalytic performance.

An in situ approach to preparing Ni2P/SiO2 catalyst under mild conditions and its performance for the deoxygenation of methyl laurate to hydrocarbons

An in situ approach was explored to prepare Ni₂P/SiO₂ from Ni/SiO₂via a phosphorization process using triphenylphosphine as the phosphorus source.

Novel thiotolerant catalysts for the on-board partial dehydrogenation of jet fuels

The possibility of producing on-board H₂ by dehydrogenation of petrol derivates is interesting for transport applications.

Hydrodechlorination of polychlorinated molecules using transition metal phosphide catalysts

Ni2P and CoP catalysts (5 wt.% of metal) supported on a commercial SiO2 were tested in the gas phase catalytic hydrodechlorination (HDCl) of mono (chlorobenzene-ClB) and polychlorobenzenes (PCBs) (1,2- dichlorobenzene (1,2-DClB), 1,3-dichlorobenzene (1,3-DClB), 1,4-dichlorobenzene (1,4-DClB), and 1,2,4-trichlorobenzene (1,2,4-TClB)) at atmospheric pressure. It was investigated how the number and position of chlorine atoms in the molecule influence the HDCl activity. The prepared catalysts were characterized by X-ray diffraction (XRD), CO chemisorption, N2 adsorption-desorption at -196°C, and X-ray photoelectron spectroscopy (XPS). Characterization results indicated better active phase dispersion and greater amount of P on the Ni2P catalyst surface. Catalytic results showed that the Ni2P was more active and stable in this type of reactions. The hydrodechlorination activity decreased by increasing the number of chlorine atoms in the molecule and chlorine substituents in close proximity. The observed trend in the HDCl activity was: ClB>1,4-DClB>1,3-DClB>1,2-DClB>1,2,4-TClB. The exception was the catalytic response after 24h on stream observed for the Ni2P in the HDCl reaction of 1,2,4-TClB, which was equal to that observed for the 1,4-DClB molecule, and also yielding benzene as the main reaction product.

A facile approach to enhancing activity of Ni2P/SiO2 catalyst for hydrodechlorination of chlorobenzene: promoting effect of water and oxygen

The Ni₂P/SiO₂ activity for the hydrodechlorination of chlorobenzene was remarkably enhanced by the treatment with H₂O or O₂.

Gas phase catalytic hydrodechlorination of chlorobenzene over cobalt phosphide catalysts with different P contents

The gas phase catalytic hydrodechlorination (HDC) of chlorobenzene (CB) at atmospheric pressure was investigated over silica-supported cobalt and cobalt phosphide catalysts containing different P loading and a fixed amount of cobalt (5 wt.%). The effect of the initial P/Co molar ratio on the stoichiometry of the cobalt phosphide phase, the acidity and the hydrogen activation capability were discussed and these properties correlated with the catalytic activity. Catalytic results indicated that the cobalt phosphide phase is much more active than the monometallic cobalt one. The activity raised with the P content present in the sample due to the formation of the CoP phase instead of the Co₂P one, which favored the formation of hydrogen spillover species, increased the amount of weak acid sites and the number of exposed superficial cobalt atoms probably related to a better dispersion of the active phase. All the catalysts gave rise benzene as the main reaction product.

Reductive transformation of endosulfan in aqueous phase using magnesium-palladium bimetallic systems: a comparative study

The efficiencies of reductive transformation of endosulfan by bimetallic systems consisting of zerovalent magnesium (Mg(0)) as the electron donor and three forms of palladium as the catalyst (Pd(0)-alumina, Pd(0)-carbon and Pd-K(2)PdCl(6)) were compared in this investigation. Results revealed that both Pd(0)-alumina and Pd(0)-carbon were able to remove 90 and 93% of 10 mg L(-1) of endosulfan, respectively in 30 min with the concomitant accumulation of trace concentrations of partially chlorinated compounds in the reaction medium. Removal of endosulfan followed first-order kinetics and the rate constant (k(obs)) value was computed to be 0.2 min(-1) for both Pd(0)-alumina and Pd(0)-carbon. Pd(0)-carbon was relatively more stable and reusable in comparison to Pd(0)-alumina. More than 99% of 10 mg L(-1) endosulfan was converted to hydrocarbon end product by Pd-K(2)PdCl(6) system within 6 min of reaction. The formation of hydrocarbon end product suggested desulfurization and complete dechlorination of endosulfan. The efficiencies of removal of α and β endosulfan isomers were nearly the same in reaction media containing acetone or Tween 80 as the pesticide solubilizing agents. Results obtained in this study suggest the possibility of developing a reactor containing immobilized palladium for the treatment of water contaminated with endosulfan.

Nano-scale Au supported on Fe3O4: characterization and application in the catalytic treatment of 2,4-dichlorophenol

Catalytic hydrodechlorination (HDC) is an effective means of detoxifying chlorinated waste. Gold nanoparticles supported on Fe(3)O(4) have been tested in the gas phase (1 atm, 423 K) HDC of 2,4-dichlorophenol. Two 1% w/w supported gold catalysts have been prepared by: (i) stepwise deposition of Au on α-Fe(2)O(3) with subsequent temperature-programmed reduction at 673 K (Au/Fe(3)O(4)-step); (ii) direct deposition of Au on Fe(3)O(4) (Au/Fe(3)O(4)-dir). TEM analysis has established the presence of Au at the nano-scale with a greater mean diameter (7.6 nm) on Au/Fe(3)O(4)-dir relative to Au/Fe(3)O(4)-step (4.5 nm). We account for this difference in terms of stronger (electrostatic) precursor/support interactions in the latter that can be associated with the lower pH point of zero charge (with respect to the final deposition pH) for Fe(2)O(3). Both catalysts promoted the preferential removal of the ortho-Cl substituent in 2,4-dichlorophenol, generating 4-chlorophenol and phenol as products of partial and total HDC, respectively, where Au/Fe(3)O(4)-step delivered a two-fold higher rate (2 × 10(-4) mol(Cl) h(-1) m(Au)(-2)) when compared with Au/Fe(3)O(4)-dir. This unprecedented selectivity response is attributed to activation of the ortho-C-Cl bond via interaction with electron-deficient Au nanoparticles. The results demonstrate the feasibility of a controlled recovery/recycling of chlorophenol waste using nano-structured Au catalysts.