(291b) Elucidating the Role of Alkaline Earth Metal Promoters and Zeolite Support Acidity on Palm Oil Catalytic Upgrading: Insights from DFT and Reactive Molecular Dynamics

Over the past decades, a shift to biomass conversion technologies has been observed to counteract the negative effects of a fossil fuel-based economy [1]. Palm oil, an abundantly present agricultural biomass, holds the potential of producing biofuels that can be used as drop-in alternatives to fossil fuel hydrocarbons [2][3]. Among the various biomass conversion routes, fast pyrolysis is regarded as an economical biomass-to-fuel method with up to 70% wt. produced liquid product, known as bio-oil [4]. However, a major drawback of bio-oil direct use is its highly oxygenated nature, causing its lower energy density compared to fossil fuels [5]. Thus, O-removal using a HDO process is a promising route to stabilize long-chain bio-oils for commercial applications as biodiesel fuels [3], or as feedstocks for the production of added-value products [6][7].

A variety of heterogenous microporous heterogeneous catalysts have been investigated for the HDO of modeled palm oil compounds [3,8–10]. Among such structures, tuned aluminosilicates incorporated with metal sites, have attracted great attention towards the decarboxylation/decarbonylation (deCOx) and hydrodeoxygenation (HDO) of bio-oils catalytic upgrading [8,11–14]. Despite recent experimental studies, the upgrading of long-chain palm oil compounds has not yet been explored computationally. Thus, it remains unclear how the competitive mechanism proceeds to take place on the catalyst active-sites.

In this work, the upgrading of oleic acid and palmitic acids, two representative modelled palm oil molecules, have been examined using DFT calculations and ReaxFF simulations to study the role of (1) alkaline earth metal promoters on Ni(111) surface and examine the (2) activity of Brønsted–acid sites incorporated into (001) and (100) BEA-zeolite support. The Results from DFT reflected the effect of Mg²⁺ on improving the bio-oils’ adsorption energy, reducing the O−M separation distance, and elongating the C−O bond length towards HDO upgrading. Notably, correlating the periodic number of the ionic promoter active-sites with the palmitic acid adsorption energy and O−M separation provided a linear relationship with R²=0.988 and R²=0.987. Such derived linear correlations are valuable in further anticipating the reactivity trends of transition metal-based modified catalysts. Moreover, ReaxFF simulations demonstrated the greater deCOx reactivity of BEA(100) compared to (001), revealing the molecular-level interactions governing the aggregation of oleic acid and palmitic acid on both facets. Aside from the effect of facets, different Si/Al ratios (all-silica, Si/Al=7, and 15), reaction temperatures (300K, 700K, and 1200K), and feedstocks (bio-oil/dodecane) were tackled. The protonated sites induced the zeolite activity as depicted by the higher number of CO/CO₂ and H₂O produced, also signified by elevated O_OleicAcid-H_BEA g(r) peaks and reduced separation distances. Besides, the presence of dodecane gave rise to the bio-oils conversion and hydrocarbon yields quantitatively examined by the ratio of C_feedstock/C_{hydrocarbon-fuels} production. Although increasing the temperature from 700K to 1200K enhanced the palmitic acid and oleic acid conversions, a reduction in n-C₁₆ and n-C₁₈ yields was found coupled with higher ethylene production. This contribution deepens the fundamental understanding, at the molecular level, of the role of modified nickel surfaces and tuned BEA-zeolite supports to pinpoint the optimum factors governing the catalytic upgrading of long-chain bio-oil feedstocks towards value-added hydrocarbons and potential biofuels.

This work has been partially financed by Khalifa University of Science and Technology under the Research and Innovation Center on CO₂ and Hydrogen (RICH) and the Catalysis and Separation Center (CeCaS) (projects RC2-2019-007 and RC2-2018-024, and AARE19-223).

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