2 research outputs found
Low-Temperature Catalytic CO<sub>2</sub> Dry Reforming of Methane on Ni-Si/ZrO<sub>2</sub> Catalyst
The
activity of a ZrO<sub>2</sub>-supported nickel catalyst promoted by
silica (Ni-Si/ZrO<sub>2</sub>) in CO<sub>2</sub> dry reforming of
methane was carried out at 400 and 450 °C. The catalysts were
prepared by an impregnation method and characterized by H<sub>2</sub>-TPR, XRD, TEM, TG-MS, Raman, XPS, and in situ XPS and DRIFTS. It
was discovered that Ni-Si/ZrO<sub>2</sub> showed higher initial conversion
of CH<sub>4</sub> (0.50 s<sup>–1</sup>) and CO<sub>2</sub> (0.44
s<sup>–1</sup>), and stability for low temperature (400 °C)
DRM reaction in comparison to an SiO<sub>2</sub>-supported nickel
catalyst promoted by zirconia (Ni-Zr/SiO<sub>2</sub>) (0.32 s<sup>–1</sup> for both CO<sub>2</sub> and CH<sub>4</sub>). The
Ni-Si/ZrO<sub>2</sub> catalyst featured the formation of active nickel
particles with a small size of 6–9 nm and with slightly strong
electronic donor ability, stabilization of the initial metal nickel
state under the reaction conditions, and the formation of easily removed
C<sub>1</sub> coke. However, for the 450 °C DRM reaction, the
coke that formed on the Ni-Si/ZrO<sub>2</sub> catalyst was mainly
C<sub>2</sub> coke that was difficult to remove, because the CO<sub>2</sub> preferred to combine with H species rather than react with
the coke. For the Ni-Zr/SiO<sub>2</sub> catalyst, the Ni<sup>0</sup> species was oxidized to a NiO species under the reaction conditions
at 400 °C and could not be restored, leading to its deactivation
Chemical Space Covered by Applicability Domains of Quantitative Structure–Property Relationships and Semiempirical Relationships in Chemical Assessments
A significant number of chemicals registered in national
and regional
chemical inventories require assessments of their potential “hazard”
concerns posed to humans and ecological receptors. This warrants knowledge
of their partitioning and reactivity properties, which are often predicted
by quantitative structure–property relationships (QSPRs) and
other semiempirical relationships. It is imperative to evaluate the
applicability domain (AD) of these tools to ensure their suitability
for assessment purpose. Here, we investigate the extent to which the
ADs of commonly used QSPRs and semiempirical relationships cover seven
partitioning and reactivity properties of a chemical “space”
comprising 81,000+ organic chemicals registered in regulatory and
academic chemical inventories. Our findings show that around or more
than half of the chemicals studied are covered by at least one of
the commonly used QSPRs. The investigated QSPRs demonstrate adequate
AD coverage for organochlorides and organobromines but limited AD
coverage for chemicals containing fluorine and phosphorus. These QSPRs
exhibit limited AD coverage for atmospheric reactivity, biodegradation,
and octanol–air partitioning, particularly for ionizable organic
chemicals compared to nonionizable ones, challenging assessments of
environmental persistence, bioaccumulation capability, and long-range
transport potential. We also find that a predictive tool’s
AD coverage of chemicals depends on how the AD is defined, for example,
by the distance of a predicted chemical from the centroid of the training
chemicals or by the presence or absence of structural features