Effect of Manganese on the Selective Catalytic Hydrogenation of CO_x in the Presence of Light Hydrocarbons Over Ni/Al₂O₃: An Experimental and Computational Study

Abstract

The promoting effect of manganese on the Ni/Al2O3 catalyst for the hydrogenation of carbon oxides, in the presence of light hydrocarbons, was studied. Ni/Al2O3 displayed a high activity for the complete conversion of CO and CO2 to methane and C2+ hydrocarbons. Moreover, over a discrete and relatively narrow temperature range, the net concentration of light C2+ hydrocarbons was elevated, with the exit stream containing a higher concentration of C2+ species than was present in the feed stream and the product stream being virtually free of carbon oxides. It is found that the addition of manganese can enhance the selectivity toward the production of light hydrocarbons. A series of Ni–Mn/Al2O3 catalysts, prepared with different Ni/Mn ratios, were studied. Various characterization techniques such as X-ray diffraction (XRD) analysis, CO and H2 chemisorption, in situ nitric oxide adsorption Fourier transform infrared spectroscopy (NO-FTIR), and temperature-programmed reduction (TPR) were performed to gain an insight into how the addition of Mn to the primary catalyst enhances the yield of light hydrocarbons. The origin of Mn promotion was demonstrated through density functional theory (DFT) calculations, which revealed the favorable Mn substitution at the Ni(211) step edge sites under reducing conditions. The affinity of these Mn species toward oxidation stabilizes the CO dissociation product and thus provides a thermodynamic driving force that promotes C–O bond cleavage compared to the Mn-unmodified catalyst surface.

Highly Effective Activated Carbon‐Supported Ni‐Mn Bifunctional Catalyst for Selective Hydrodeoxygenation of 5‐Hydroxymethylfurfural to 2,5‐Dimethylfuran

“…At 140 °C for 4 h, 80.0 % 5‐HMF was converted, and 68.6 % 2,5‐DMF yield was obtained over Ni‐Mn(3 : 1) catalyst (entry 4). For all the Mn‐containing Ni catalysts, 2,5‐DMF yields beyond 90 % were achieved at 180 °C, and the intermediate DHMF was not detected, which is consistent with the previous report that the additive MnO x in the catalyst could accelerate the dissociation of C−O [26] . It can be seen that the performance of the Ni‐Mn catalysts increased with the decrease in Ni/Mn molar ratio from 4 : 1 to 3 : 1 (entries 6 and 7), and the highest 2,5‐DMF yield of 98.5 % with a 5‐HMF conversion of 100 % was achieved over Ni‐Mn(3 : 1) catalyst.…”

“…For all the Mn-containing Ni catalysts, 2,5-DMF yields beyond 90 % were achieved at 180 °C, and the intermediate DHMF was not detected, which is consistent with the previous report that the additive MnO x in the catalyst could accelerate the dissociation of CÀ O. [26] It can be seen that the performance of the Ni-Mn catalysts increased with the decrease in Ni/Mn molar ratio from 4 : 1 to 3 : 1 (entries 6 and 7), and the highest 2,5-DMF yield of 98.5 % with a 5-HMF conversion of 100 % was achieved over Ni-Mn(3 : 1) catalyst. Upon further increasing the Mn content, as in the case of Ni-Mn(2 : 1) (entry 8), 2,5-DMF yield decreased, and ring-opening by-products such as acetonylacetone and 2-hexanol were detected.…”

Nano-Sized NiO Immobilized on Au/CNT for Benzyl Alcohol Oxidation: Influences of Hybrid Structure and Interface

“…Decoration of CNT by NiO: A series of Ni x /CNT catalysts with different Ni atomic ratios were prepared by the impregnation method, similar to the reported literature [ 43 ]. The concentration of the aqueous solution of nickel nitrite was fixed at 0.513 mol/L.…”

Ruthenium isomorphic substitution into manganese oxide octahedral molecular sieve OMS-2: Comparative physic-chemical and catalytic studies of Ru versus abundant metal cationic dopants

“…This experimental fact can be explained if we take into account that reduction processes in TPR-H 2 studies may involve not only phase changes but also formation of highly stable species by reaction with certain cationic dopants (i.e. formation of allotropic oxides forms in the case of Ni and Fe) [69,70]. These highly stable species would consume an extra amount of H 2 therefore preventing this correlation from taking place in the case of Fe and Ni.…”