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Hydrodeoxygenation (HDO) reaction is a route with much to offer in the conversion and upgrading of bio-oils into fuels; the latter can potentially replace fossil fuels. The catalyst’s design and the feedstock play a critical role in the process metrics (activity, selectivity). Among the different classes of catalysts for the HDO reaction, the transition metal phosphides (TMP), e.g., binary (Ni2P, CoP, WP, MoP) and ternary Fe-Co-P, Fe-Ru-P, are chosen to be discussed in the present review article due to their chameleon type of structural and electronic features giving them superiority compared to the pure metals, apart from their cost advantage. Their active catalytic sites for the HDO reaction are discussed, while particular aspects of their structural, morphological, electronic, and bonding features are presented along with the corresponding characterization technique/tool. The HDO reaction is critically discussed for representative compounds on the TMP surfaces; model compounds from the lignin-derivatives, cellulose derivatives, and fatty acids, such as phenols and furans, are presented, and their reaction mechanisms are explained in terms of TMPs structure, stoichiometry, and reaction conditions. The deactivation of the TMP’s catalysts under HDO conditions is discussed. Insights of the HDO reaction from computational aspects over the TMPs are also presented. Future challenges and directions are proposed to understand the TMP-probe molecule interaction under HDO process conditions and advance the process to a mature level.

Achieving ultradeep desulfurization of transportation fuels dictates the removal of the last fragments of sulfur present in bulky refractory molecules such as dibenzothiophene (DBT). Improving the hydrodesulfurization (HDS) performance of the next-generation Ni 2 P catalyst is crucial; however, it is still unclear how a DBT direct desulfurization (DDS) reaction proceeds on different surface terminations of this material. This work aims at elucidating the influence of Ni 3 P-, Ni 3 P 2 -, and partially sulfided Ni 3 P 2 (Ni 3 PS)-terminated surfaces of the Ni 2 P(001) crystal on the DDS reaction of DBT using density functional theory (DFT) computations. The scission of the first C−S bond in DBT was found to be kinetically hindered compared to the second C−S bond cleavage over the three surfaces owing to the highly stable structure of adsorbed DBT compared to the C 12 H 9 SH intermediate. Notably, the overall DBT desulfurization process is thermodynamically favorable only on the Ni 3 PS surface, due to the presence of the active phosphosulfide (Ni−P−S) phase. Microkinetic modeling was conducted to probe the reaction orders, apparent activation energy, and rate-controlling steps as a function of temperature. Notably, the ring-opening step of DBT, via the first C−S bond cleavage, is the rate-controlling step on Ni 3 P and Ni 3 PS surfaces, which is rationalized by the high energy barrier of this step. The activation energy of the reaction over the surfaces followed the order Ni 3 P < Ni 3 PS < Ni 3 P 2 . Compared to the bare Ni 3 P 2 surface, the lower activation energy on the Ni 3 PS surface is explained by the destabilization effect of the reaction intermediates on the latter. Thus, the partially sulfided Ni 3 P 2 provides a better model for the DBT desulfurization process than the fresh Ni 3 P 2 surface.

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We developed a set of tools for visualizing, analyzing, and editing reaction networks. Three conceptual elements were covered. In the first, the reaction network was rendered in terms of species−species and species−reaction tree plots. This provided for a visual inspection of the connectivity of components in a reaction network and the paths from reactants to products. More quantitative information was provided by the second element, which represented the quantitative concentration of the composition as it evolved from reactants to products. This allowed the modeler to examine the quantitative flows of mass though the reaction network and expose flaws for editing. The third element involved a coupling of the tree visualization and model solution tools that allowed for the elimination of reactions and rebuilding of the reaction network from the visualization interface. These tools are illustrated using the production of butadiene through catalytic oxidative dehydrogenation of butane as an example.

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In this study, we investigated the Ni/CeO 2 /Al 2 O 3 catalyst system to explore the influence of different synthesis parameters on interfacial phenomena and their impact on CO 2 methanation. The focus was on the textural properties of alumina, ceria loading, and the synthesis method of supported Ni, in relation to the catalyst's activity and CH 4 selectivity. Among the catalysts studied, Ni−20Ce/mpAl demonstrated promising results, with an X CO2 value of 70% and S CH4 value exceeding 94% at 350 °C. We observed that medium-and high-porosity alumina facilitated better ceria dispersion, while Ni-CeO 2 cogrowth led to small Ni crystallites (∼4 nm) that increased in size after 8 h of reaction. This catalyst exhibited several advantageous features for CO 2 methanation, including a high concentration of oxygen vacancies (confirmed through Raman studies) and a significant presence of surface Ce 3+ species (validated by XPS and EPR studies). It also displayed excellent carbonyl activation capacity, high H-spillover capability, and strong SMSI phenomena. CO 2 -TPD and charge transfer Bader analysis confirmed the basic (Lewis) character of the catalyst's surface. Specifically, Ce 3+ species, along with Ni atoms, provided suitable dual sites for CO 2 adsorption at the Ni-ceria interface, forming Ni•••O−C−O•••Ce 3+ entities. Furthermore, our analysis using operando SSITKA-DRIFTS revealed the active participation of both Ni and the support in the CO 2 methanation reaction, validating the ab initio studies. Notably, linear and bridged adsorbed CO species (CO L and CO B ) on the Ni surface, as well as bicarbonates (HCOOOs), were identified as active reaction intermediates involving Ce 3+ −OH and Al 3+ −OH entities. Comparing the thermal stability of carbonate-type intermediates to that of carbonyls, a CO-mediated mechanism emerged as the predominant pathway over the Ni−20Ce/mpAl catalyst.