Our
contribution demonstrates that rhodium, an element that has
barely been reported as an active metal for selective dehydrogenation
of alkanes becomes a very active, selective, and robust dehydrogenation
catalyst when exposed to propane in the form of single atoms at the
interface of a solid-supported, highly dynamic liquid Ga–Rh
mixture. We demonstrate that the transition to a fully liquid supported
alloy droplet at Ga/Rh ratios above 80, results in a drastic increase
in catalyst activity with high propylene selectivity. The combining
results from catalytic studies, X-ray photoelectron spectroscopy,
IR-spectroscopy under reaction conditions, microscopy, and density-functional
theory calculations, we obtained a comprehensive microscopy picture
of the working principle of the Ga–Rh supported catalytically
active liquid metal solution.
Supported catalytically
active liquid metal solutions (SCALMS)
of Pt in Ga (2 at.-% Pt) were studied in the temperature range of
500 to 600 °C for propane dehydrogenation. A facile synthesis
procedure using ultrasonication was implemented and compared to a
previously reported organo-chemical route for gallium deposition.
The procedure was applied to synthesize GaPt-SCALMS catalyst on silica
(SiO
2
), alumina (Al
2
O
3
), and silicon
carbide (SiC) to investigate the effect of the support material on
the catalytic performance. The SiC-based SCALMS catalyst showed the
highest activity, while SiO
2
-based SCALMS showed the highest
stability and lowest cracking tendency at higher temperatures. The
selectivity toward propene for the SiO
2
-based catalyst
remained above 93% at 600 °C. The catalysts were analyzed for
coke content after use by temperature-programmed oxidation (TPO) and
Raman spectroscopy. While the SiC- and SiO
2
-supported SCALMS
systems showed hardly any coke formation, the Al
2
O
3
-supported systems suffered from pronounced coking. SEM-EDX
analyses of the catalysts before and after reaction indicated that
no perceivable morphological changes occur during reaction. The SCALMS
catalysts under investigation are compared with supported Pt and supported
GaPt solid-phase catalyst, and possible deactivation pathways are
discussed.
Supported Catalytically Active Liquid Metal Solutions (SCALMS) were recently described as a new class of heterogeneous catalysts, where the catalytic transformation takes place at the highly dynamic interface of a liquid alloy. Their application in alkane dehydrogenation has been claimed to be superior to classical heterogeneous catalysts, because the single atom nature of Rh dissolved in liquid Ga hinders the formation of significant amounts of coke, e. g. by oligomerisation of carbon fragments and excessive dehydrogenation. In the present study, we investigate the coking behaviour of Ga−Rh SCALMS during dehydrogenation of propane in detail by means of high‐resolution thermogravimetry. We report that the application of Ga−Rh SCALMS indeed limits the formation of coke when compared to the Ga‐free Rh catalyst, in particular when relating coke formation to the catalytic performance. Furthermore, the formed coke has been shown to be highly reactive during temperature programmed oxidation in 21 % O2/He with onset temperatures of approx. 150 °C enabling a regeneration of the Ga−Rh SCALMS system under mild conditions. The activation energy of the oxidation lies in the lower range of values reported for spent cracking catalysts. Monitoring the formation of coke and performance of SCALMS in situ via thermogravimetry coupled with mass spectrometry revealed the continuous formation of coke, which becomes the only process affecting the net weight change after a certain time on stream.
Supported liquid phase catalysis has great potential to unify the advantages from both, homogeneous and heterogeneous catalysis. Recently, we reported Supported Catalytically Active Liquid Metal Solutions (SCALMS) as a new...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.