Xiu Chen,Ying Zhang,Jin Han,Linzhou Zhang,Suoqi Zhao,Chunming Xu,Quan Shi
The compositional analysis of heavy petroleum nickel porphyrins by electrospray ionization (ESI) is challenged by their trace amount and relatively low response. In the presented study, we developed a method to enhance the response of nickel porphyrins in ESI by introducing the electrochemical oxidation reaction. The effect of ESI type, solvent, and additives were investigated for standard compounds and heavy oils. The results showed that the ESI source with high positive needle voltage is suitable for nickel porphyrins analysis using dichloromethane as the solvent and trifluoroacetic acid as the ionization promoter. Under the optimized conditions, nickel and vanadyl porphyrins can be directly ionized as molecular radical cations ([M]+•) via electrochemical oxidation due to their low oxidation potential and gas-phase ionization energy. The method is capable of direct analysis of both nickel and vanadyl porphyrins in a vacuum residue without any prior preparation. We also observed the molecular radical cations of other compounds with high aromaticity and short side chains (such as hydrocarbons, nitrogen- and sulfur-containing species), which indicate that the electrochemical oxidation reaction can be used for nonpolar compounds ESI analysis.
The heterogenized metallomacrocycles with atomically dispersed active sites are identified as the promising candidates for electrocatalytic CO 2 reduction reaction (CO 2 RR), where their unique heterointerface with interaction between sp 2 carbon and macrocyclic molecules is important but remains vague. Herein, based on well-structured nickel phthalocyanine and porphyrin with the same functional groups (MeNiPc and MeNiPp), the influences of heterointerfacial effect on catalytic performances are systematically disclosed. Through the molecular structure-induced self-adaptive adsorption with optimized heterointerfacial distance, MeNiPc/graphene reveals a high CO Faradaic efficiency of ~99% in a wide potential window, greatly outperforming the MeNiPp/graphene counterpart (≤29.6%). Detailed measurements and theoretical calculations decipher that the higher CO 2 RR activity of MeNiPc/graphene is attributed to the unique electronic structures of the Ni-N 4 configurations suitable for well-suited heterointerfacial charge transfer and rapid CO desorption. Additionally, the extended research confirms the universality of heterointerface engineering on boosting the catalytic performances.
Metalloporphyrins are organic compounds found in petroleum that form complexes with transition metals, such as vanadium and nickel. These complexes are detrimental to catalytic cracking and hydrotreating catalysts. The identification and removal of vanadium and nickel porphyrins from petroleum have been extensively explored. In this work, the axial coordination interaction of nickel octaethylporphyrin (NiOEP) with various ligands has been investigated using experimental and computational methods. The five- and six-coordinated complexes formed by NiOEP with mono- and bis-ligands, respectively, were studied and compared. Changes in the ultraviolet-visible (UV-Vis) spectra, specifically the location and intensity of the Soret band of NiOEP upon ligand addition, were mainly attributed to the formation of six-coordinated complexes, which were consistent with the results of binding energies and simulated excited states calculated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The axial coordination ability of different ligands with NiOEP is closely related to the basicity and steric hindrance of the ligands, whereas the binding energies and relative stability of the coordinated complexes are correlated with the basicity of the ligands. In addition to the five- and six-coordinated complexes, the complexes formed by bis-NiOEP and mono-ligands (2 : 1 adduct) were also observed and characterized using high-resolution mass spectrometry (HR MS) combined with the collision-induced dissociation (CID) technique.
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