Dali Qian

Unlike on Fe and Co catalysts, the CO conversion effect on Ru catalyst performance is little reported. This study is undertaken to explore the issue using a series of Ru/NaY catalysts under 200–230 °C, 2.0 MPa, H₂/CO = 2, and 10–60% CO conversion in a 1 L continuous stirred tank reactor (CSTR). The results are comparatively studied with those of Fe and Co catalysts reported previously. The NaY support and four 1.0%, 2.5%, 5.0%, and 7.5% Ru/NaY catalysts were characterized by BET, H₂ chemisorption, H₂O-TPD, XRD, HRTEM, and XANES/EXAFS techniques. The BET and XRD results suggest a high surface area (730 m²/g), high degree of crystallinity of the NaY support, and high dispersion of Ru, while an hcp Ru structure and well-reduced Ru were reflected in the HR-TEM FFT and XANES/EXAFS results. The reaction results indicate that the CO conversion effect on CH₄ and C₅₊ selectivities on the Ru is the same as that on the Fe and Co catalysts, with CH₄ selectivity decreasing and C₅₊ selectivity increasing with increasing CO conversion. However, the CO conversion effect on olefin formation for the Ru catalyst was found to be opposite to that of the Fe and Co; increasing CO conversion enhanced olefin formation but suppressed secondary reactions of 1-olefins. The H₂O cofeeding experiments showed that H₂O impacted olefin formation by suppressing hydrogen adsorption and hydrogenation. The H₂O-TPD experiment evidenced a much stronger H₂O adsorption capacity (6.8 mmol/g-cat) on Ru followed by Co (1 mmol/g-cat), and then Fe (0.2 mmol/g-cat)., which showed only a very low H₂O adsorption capacity.This finding may explain the opposite CO conversion effect on olefin formation observed on the Ru catalyst, and may also explain why low CH₄ selectivity (i.e., 3%) occurred on the Ru catalyst and high CH₄ selectivity (i.e., 6–8%) occurred on the Co catalyst, both of which possess low water gas shift (WGS) activity.

This study investigates the effect of potassium (K) promotion on Pt/m-ZrO₂ catalysts in methanol steam reforming (MSR), revealing critical insights into reaction pathways and catalyst performance. While increasing K loading reduces catalytic activity, it selectively enhances the hydrogen-producing formate dehydrogenation and de-carboxylation pathway. Structural analyses using HR-TEM and DRIFTS show that higher K concentrations block Pt sites and promote agglomeration, reshaping catalytic behavior. Notably, the 3.1% K-promoted catalyst achieves high stability at 358 °C, with a CO₂ selectivity exceeding 80% and minimal methane formation, outperforming the unpromoted catalyst in terms of CO and CH₄ selectivity. Temperature studies further demonstrate reduced CO selectivity at higher temperatures, highlighting distinct advantages of K-doped catalysts. These findings underscore the role of K in enhancing surface basicity and its impact on formate interaction, offering valuable insights for optimizing MSR catalysts and advancing hydrogen production technologies.

In this study, the effect of media composition, N/P ratio and cultivation strategy on the formation of carotenoids in a Coelastrella sp. isolate was investigated. A two-stage process utilizing different media in the vegetative stage, with subsequent re-suspension in medium without nitrate, was employed to enhance the formation of carotenoids. The optimal growth and carotenoid content (β-carotene and lutein) in the vegetative phase were obtained by cultivation in M-8 and BG11 media. Use of a N/P ratio of 37.5 and low light intensity of 40 μmol m⁻² s⁻¹ (control conditions) led to optimal biomass production of up to 1.31 g L⁻¹. Low concentrations of astaxanthin (maximum of 0.31 wt. %) were accumulated under stress conditions (nitrogen-deficient medium containing 1.5 % of NaCl and light intensity of 500 μmol m⁻² s⁻¹), while β-carotene and lutein (combined maximum of 2.12 wt. %) were produced under non-stress conditions. Lipid analysis revealed that palmitic (C16:0) and oleic (C18:1) constituted the main algal fatty acid chains (50.2 ± 2.1% of the total fatty acids), while esterifiable lipids constituted 17.2 ± 0.5% of the biomass by weight. These results suggest that Coelastrella sp. could also be a promising feedstock for biodiesel production.

Examination of a fly ash derived from the combustion of a low-S, subbituminous Powder River Basin coal by Scanning Electron Microscopy (SEM) and High-resolution Transmission Electron Microscopy (HRTEM), both supplemented by Energy-dispersive X-ray spectroscopy (EDS), showed that the fly ashes were dominated by amorphous phases, Ca-rich plagioclase feldspars, Mg-rich phases, complex Ca-Mg-Al-Si-Ti-Fe grains, and trace amounts of REE-rich particles. Many of the particles were rimmed by a Ca-S, possibly a sulfate. HRTEM-EDS examination of a REE-rich particle proved it to be a mix of light- and heavy-rare earth minerals mixed with amorphous phases.

The decarboxylation pathway in ethanol steam reforming ultimately favors higher selectivity to hydrogen over the decarbonylation mechanism. The addition of an optimized amount of Cs to Pt/m-ZrO₂ catalysts increases the basicity and promotes the decarboxylation route, converting ethanol to mainly H₂, CO₂, and CH₄ at low temperature with virtually no decarbonylation being detected. This offers the potential to feed the product stream into a conventional methane steam reformer for the production of hydrogen with higher selectivity. DRIFTS and the temperature-programmed reaction of ethanol steam reforming, as well as fixed bed catalyst testing, revealed that the addition of just 2.9% Cs was able to stave off decarbonylation almost completely by attenuating the metallic function. This occurs with a decrease in ethanol conversion of just 16% relative to the undoped catalyst. In comparison with our previous work with Na, this amount is—on an equivalent atomic basis—just 28% of the amount of Na that is required to achieve the same effect. Thus, Cs is a much more efficient promoter than Na in facilitating decarboxylation.

Inexpensive Ni-based catalysts can afford comparable performance to costly precious metal formulations in the conversion of fat, oil, or greases (FOG) to fuel-like hydrocarbons via decarboxylation/decarbonylation (deCO_x). While the addition of certain metals has been observed to promote Ni-based deCO_x catalysts, the steady-state performance of bimetallic formulations must be ascertained using industrially relevant feeds and reaction conditions in order to make meaningful comparisons. In the present work, used cooking oil (UCO) was upgraded to renewable diesel via deCO_x over Ni/Al₂O₃ promoted with Cu, Fe, or Pt in a fixed-bed reactor at 375 °C using a weight hourly space velocity (WHSV) of 1 h⁻¹. Although all catalysts fully deoxygenated the feed to hydrocarbons throughout the entire 76 h duration of these experiments, the cracking activity (and the evolution thereof) was distinct for each formulation. Indeed, that of the Ni-Cu catalyst was low and relatively stable, that of the Ni-Fe formulation was initially high but progressively dropped to become negligible, and that of the Ni-Pt catalyst started as moderate, varied considerably, and finished high. Analysis of the spent catalysts suggests that the evolution of the cracking activity can be mainly ascribed to changes in the composition of the metal particles.

Fly ash from the combustion of eastern Kentucky Fire Clay coal in a southeastern United States pulverized-coal power plant was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). TEM combined with elemental analysis via energy dispersive X-ray spectroscopy (EDS) showed that rare earth elements (REE; specifically, La, Ce, Nd, Pr, and Sm) were distributed within glassy particles. In certain cases, the REE were accompanied by phosphorous, suggesting a monazite or similar mineral form. However, the electron diffraction patterns of apparent phosphate minerals were not definitive, and P-lean regions of the glass consisted of amorphous phases. Therefore, the distribution of the REE in the fly ash seemed to be in the form of TEM-visible nano-scale crystalline minerals, with additional distributions corresponding to overlapping ultra-fine minerals and even true atomic dispersion within the fly ash glass.

Pt represents an effective promoter of supported Ni catalysts in the transformation of tristearin to green diesel via decarbonylation/decarboxylation (deCO_x), conversion increasing from 2% over 20% Ni/Al₂O₃ to 100% over 20% Ni-0.5% Pt/Al₂O₃ at 260 °C. Catalyst characterization reveals that the superior activity of Ni-Pt relative to Ni-only catalysts is not a result of Ni particle size effects or surface area differences, but rather stems from several other phenomena, including the improved reducibility of NiO when Pt is present. Indeed, the addition of a small amount of Pt to the supported Ni catalyst dramatically increases the amount of reduced surface metal sites, which are believed to be the active sites for deCO_x reactions. Further, Pt addition curbs the adsorption of CO on the catalyst surface, which decreases catalyst poisoning by any CO evolved via decarbonylation, making additional active sites available for deoxygenation reactions and/or preventing catalyst coking. Specifically, Pt addition weakens the Ni-CO bond, lowering the binding strength of CO on surface Ni sites. Finally, analysis of the spent catalysts recovered from deCO_x experiments confirms that the beneficial effect of Pt on catalyst performance can be partially explained by decreased coking and fouling.

While commercial hydrodeoxygenation (HDO) processes convert fats, oils, and grease (FOG) to fuel-like hydrocarbons, alternative processes based on decarboxylation/decarbonylation (deCO_x) continue to attract interest. In this contribution, the activity of 20% Ni-5% Cu/Al₂O₃ in the deCO_x of waste free fatty acid (FFA)-based feeds—including brown grease (BG) and an FFA feed obtained by steam stripping a biodiesel feedstock—was investigated, along with the structure-activity relationships responsible for Ni promotion by Cu and the structural evolution of catalysts during use and regeneration. In eight-hour experiments, near quantitative conversion of the aforementioned feeds to diesel-like hydrocarbons was achieved. Moreover, yields of diesel-like hydrocarbons in excess of 80% were obtained at all reaction times during a BG upgrading experiment lasting 100 h, after which the catalyst was successfully regenerated in situ and found to display improved performance during a second 100 h cycle. Insights into this improved performance were obtained through characterization of the fresh and spent catalyst, which indicated that metal particle sintering, alloying of Ni with Cu, and particle enrichment with Cu occur during reaction and/or catalyst regeneration.