P. Michael Boorman

Phosphorus promotion in nickel-molybdenum/alumina catalysts: model compound reactions and gas oil hydroprocessing

Abstract Three different preparation methods for Ni-Mo/Al 2 O 3 catalysts containing between 0 and 7.0 wt.-% phosphorus are compared in thiophene hydrodesulphurization (HDS) and diisopropylbenzene (DIPB) hydrocracking reactions. A promotional effect of phosphorus is seen in thiophene HDS regardless of preparation method, with maximum activity at around 1 wt.-% phosphorus. P/Al 2 O 3 catalysts (P = 0–7 wt.-% ) have little activity in DIPB hydrocracking indicating that phosphorus has very little effect on the Bronsted acidity of alumina. An increase in DIPB hydrocracking is observed for P-Ni-Mo catalysts with low phosphorus loadings, however, and so phosphorus does have an indirect effect on the Bronsted acidity of these catalysts. Impregnation of phosphorus prior to the metal species leads to the most active catalysts for both thiophene HDS and DIPB hydrocracking and this is explained in terms of a dual promotional effect of phosphorus; phosphorus increases both the dispersion and reducibility/sulphidibility of molybdate and increases the amount of nickel available to form the Ni-Mo-S active HDS phase by impeding nickel aluminate formation. One series of catalysts was investigated in the hydroprocessing of a Syncrude combined gas oil-fuel oil, and the same gas oil spiked with 5 vol.-% quinoline. The promotional effect of phosphorus in HDS was in good agreement with the model compound studies: 1 wt.-% phosphorus was the most active HDS catalyst in all cases. Furthermore, phosphorus loadings of between 1 and 3 wt.-% gave a product with lowest nitrogen content, and aromaticity. These loadings also gave the greatest sulphur removal and maintained good hydrogenation in the presence of quinoline, and gave the best quinoline hydrodenitrogenation, suggesting optimum surface acidity and hydrogenation properties. Optimum loadings of phosphorus (around 3 wt.-%) also improve the longevity of the catalyst by maintaining high surface area during the hydroprocessing reaction.

A comparison of alumina, carbon and carbon-covered alumina as supports for NiMoF additives: gas oil hydroprocessing studies

Abstract Catalysts with 3 wt% NiO, 15 wt% MoO 3 and 0–6.9 nominal wt% fluoride supported on alumina, carbon and carbon-covered alumina were studied to examine the role of fluoride and the influence of the support on hydroprocessing on Alberta gas oil. Experiments were carried out in a batch reactor at 410 °C and 6.9 MPa initial H 2 pressure. It was found that fluoride promotion enhances cracking and hydrogenation reactions resulting in decreased aromatic and sulphur contents in the gas oil. The promotion is dependent on the type of support and is related to the strength of the fluoride-support interaction and the accessibility of the fluoride to the surface hydroxyl groups on the support. A maximum in activity at 3.6 wt% fluoride was observed for the alumina-supported catalysts whereas higher loadings of fluoride were required for carbon-covered alumina-supported catalysts to see an improvement over their carbon supported counterparts. However, the carbon-covered alumina supported catalysts seem to have a lower propensity for coke deposition than their alumina counterparts.

NiMo/Al2O3 catalysts promoted with phosphorus and fluoride

NiMo/Al2O3 catalysts containing two promoters, fluoride and phosphorus, were studied to learn whether the benefits of both promoters could be combined to produce a superior catalyst. Initially, two series of catalysts differing in the sequence of impregnation of the additives were prepared and tested in the hydrocracking of cumene and the hydrodesulfurization of thiophene. Catalysts impregnated in the sequence phosphorus—metals (Ni and Mo)—fluoride were clearly superior to those prepared by adding first phosphorus, then fluoride and finally metals. The more effective series of catalysts was tested in the hydroprocessing of a gas oil feedstock; to determine the resistance of these surfaces to poisoning, tests were also carried out with the same feedstock spiked with quinoline. The bi-promoted catalysts retained fluoride well, and were quite effective in hydrogenation and hydrodesulfurization. They were even more effective than phoshorous-only promoted catalysts in quinoline hydrodenitrogenation.

Synthetic, structural, and spectroscopic studies of the ligating properties of organic disulphides: X-ray structure of copper(I) iodide–diethyl disulphide (2/1)

The synthesis of a series of derivatives of copper(I) halides with organic disulphides is reported. Although most of these complexes are unstable with respect to loss of ligand, the compound 2Cul·Et2S2 was sufficiently stable to be subjected to a single-crystal X-ray structure determination. Crystals are monoclinic, space group P21/n, with cell dimensions (at –100 ± 5 °C)a= 8.163(4), b= 15.651(3), c= 8.746(4)A, β= 100.73(2)°, and Z= 4. The structure was solved with data collected at –100(5)°C using direct methods followed by difference-Fourier techniques, and refined to R 0.038 (R′ 0.047) for 1 157 observed reflections. The structure consists of double chains of copper atoms bridged by two iodines, with alternative pairs of copper atoms also bridged by diethyl disulphide molecules. The geometry of the disulphide is compared with that of related complexes, and Raman spectral studies of the ν(S–S) stretching frequency of the series of complexes are reported.

Reactions of Cp2ZrH2 with Ni(dppe)(edt) and [Pd(PPh3)(edt)]2. Synthesis and structure of (Cp2Zr)2Pd(edt)2, a novel, ethanedithiolate stabilized palladium(O) complex

Abstract Both Ni(dppe)(edt) (1) (dppe = Ph2PCH2CH2PPh2; edt = ethanedithiolate) and [Pd(PPh3)(edt)]2 (2) react with zirconocene dihydride without any evidence of CS bond cleavage. Reduction of the late transition metals to the zero oxidation state occurs together with the evolution of hydrogen. For palladium the major product of the reaction is the trinuclear complex Cp2Zr(edt)Pd(edt)ZrCp2 · C6H6 (3) for which the crystal structure was determined. The structure was refined to R = 0.045 (RW = 0.032) for 2640 reflections with I > 3.0σ(I). The stereochemistry around palladium is distorted tetrahedral, and the ZrPd separations are 2.866(1) A, suggesting bonding interactions between the metals. In reactions of Cp2ZrH2 with 1, spectroscopic evidence suggested that Cp2Zr(edt)Ni(dppe) was first formed, possibly with the trinuclear nickel analogue of 3, but all attempts to recrystallize these complexes failed, and the major products isolated stemmed from ligand redistribution reactions.

Synthesis and characterization of the molybdenum(IV) oxo-selenolate complex [MoO(Ph2P(O)CH2CH2P(Ph)CH2CH2PPh2)(Se-2,4,6-(CH3)3C6H2)2]

Abstract The presence of adventitious oxygen in the reaction of [(Triphos)MoCl3] (Triphos = Ph2PCH2CH2P(Ph)CH2CH2PPh2) with NaSeC6H2Me3-2,4,6 in THF leads to the formation of [fac-MoO(Ph2P(O)CH2CH2P(Ph)CH2CH2PPh2)(SeC6H2Me3-2,4,6)2). This is the first example of a structurally characterized molybdenum(IV)oxo-selenolato complex. It contains a chelating triphosphine mono-oxide ligand. The formation can be understood in terms of an oxidative addition of dioxygen to the metal centre followed by oxygen atom transfer to the triphos ligand and reduction of molybdenum to molybdenum(IV).

Synthesis and characterization of novel molybdenum(III) confacial bioctahedral complexes: X-ray crystal structures of [Ph4P][(Me2S)-Cl2Mo(µ-Cl)3MoCl2(SMe2)] and (Me2S)Cl2Mo(µ-Me2S)(µ-Cl)2MoCl2-(SMe2)

The reaction of Et3SiH with MoCl4(Me2S)2 produces a series of isomeric molybdenum(III) complexes with the general formula Mo2Cl6(Me2S)3; X-Ray crystallographic results and/or1H n.m.r. and analytical data establish the existence of the antiferromagnetic species, (Me2S)Cl2Mo(µ-Cl)3MoCl(SMe2)2(1)[meso-and (+), (–)-forms], its chloro-anionic derivative, [Ph4P][(Me2S)Cl2Mo(µ-Cl)3MoCl2](2), and the diamagnetic complex, (Me2S)Cl2Mo(µ-Me2S)(µ-Cl)2MoCl2)(SMe2)(3).

Molybdenum(III) chloride–tetrahydrothiophene (tht) complexes in the catalytic polymerization and cyclotrimerization of alkynes: structures and reactivities of the possible intermediates [MoCl3(tht)2(PhCCR)](R = Me or Et)

The binuclear complexes [Mo2Cl6(tht)3](both the C2v and Cs isomers, tht = tetrahydrothiophene) have been found to be active catalysts for the selective polymerization and cyclotrimerization of a variety of alkynes. The mononuclear complex [MoCl3(tht)3] shows similar behaviour, leading to the postulate that the active species in all cases is mononuclear. Two unique molybdenum(III) alkyne complexes, [MoCl3(tht)2L](L = PhCCMe or PhCCEt) have been isolated and structurally characterized. The structural parameters for these complexes suggest that the alkynes behave as four-electron donors. These complexes are also catalytically active, and the alkyne L is incorporated into the product cyclotrimers and polymers suggesting they are the first intermediates in the formation of active catalysts from the original thioether complexes.

A study of supported molybdenum cluster complexes as catalyst precursors: Part II. Evaluation of the catalytic activity of clusters supported on γ-alumina and fluorided γ-alumina

Abstract The supported molybdenum clusters previously described [1] were tested for their potential activity in the catalysis of cumene hydrocracking, thiophene hydrogenolysis, propene hydrogenation and, in some instances, gas oil hydrocracking. The effect of modifying the alumina support by the addition of fluoride ion was also investigated for those materials which showed promising catalytic activity, and the molybdenum loading was varied over the calculated range 4 – 10%. The effect of cobalt and nickel promoters was then examined. The results were compared with those obtained from conventional catalysts, prepared by impregnation of γ-alumina with molybdate with and without fluoride, cobalt and nickel additives. The most active catalysts tested were those prepared from the hexanuclear cluster, (H 3 O + ) 2 [Mo 6 Cl 14 ] 2− ·6H 2 O. These catalysts gave surprisingly high conversions in cumene hydrocracking, and had substantial activity in HDS studies. As hydrocracking catalysts for application to commercial feedstocks they showed considerable promise, especially when the Mo loading factor was taken into account. XPS studies of one of this series of catalysts suggested that in the hydrocracking of cumene and in the hydrodesulfurization of thiophene, the integrity of the cluster is destroyed during use, and hence the clusters should be regarded as precursors of the active catalytic species rather than being the active species themselves.

Synthetic, structural, and spectroscopic studies of the ligating properties of organic disulphides: X-ray structures of mercury(II) chloride–dimethyl disulphide (1/1) and triethylammonium trichloromercurate

The synthesis of a series of complexes of mercury(II) halides with dimethyl and diethyl disulphide has been attempted, but of the products thereby formed, only HgCl2·Me2S2(1) was sufficiently stable to be characterised by an X-ray crystallographic structure determination. Complex (1) crystallizes in the monoclinic space group C2/c, with cell dimensions (at 20 °C)a= 14.865(4), b= 9.185(1), c= 12.441(3)A, = 109.23(1)°, and Z= 8. The structure was solved by the heavyatom method, and refined to R 0.043 (R′ 0.044) for 1 118 observed reflections. The structure consists of –Hg–Cl–Hg–Cl– chains, with the disulphide molecule loosely and asymmetrically co-ordinated in a bridging mode between adjacent pairs of mercury atoms. When using commercial Me2S2(without further purification) a crystalline by-product, [NHEt3][HgCl3](2), was unexpectediy obtained, and its structure determination was carried out to confirm its identity. Crystals of (2) are monoclinic, space group P21/n, with cell dimensions (at 20 °C)a= 7.639(2), b= 14.711(1), c= 11.074(3)A, β= 100.28(1)°, and Z= 4. The structure was refined to R 0.046 (R′ 0.033) for 1 074 observed reflections. The origin of complex (2) from the ‘HgCl2–Me2S2’ reaction is discussed.