Carbon dioxide (CO 2 ) hydrogenation to methanol with H 2 produced with renewable energy represents a promising path for the effective utilization of a major anthropogenic greenhouse gas, in which catalysts play a key role for CO 2 conversion and methanol selectivity. Although still under development, indium oxide (In 2 O 3 )-based catalysts have attracted great attention in recent years due to the excellent selectivity to methanol along with high activity for CO 2 conversion. In this review, we discuss recent advances of In 2 O 3 -based catalysts for CO 2 hydrogenation based on both experimental and computational studies. Various strategies have been adopted to improve the catalytic performance by facilitating the formation of surface oxygen vacancies (In 2 O 3−x ) as active sites, the activation of CO 2 and H 2 toward hydrogenation to methanol to mitigate reverse water−gas shift reaction, and the stabilization of the key intermediates. Mechanistic insights are gained from combining catalytic kinetic studies, in situ characterization, and theoretical investigations involving CO 2 conversion via the formate HCOO* pathway versus the carboxyl COOH* pathway. Strategies to further promote selective CO 2 hydrogenation to methanol include adding a metal component such as Pd or Ni on In 2 O 3 (which may also involve formation of bimetallic In−M catalysts) to promote H 2 activation and oxygen vacancy formation, combining In 2 O 3 with an oxide promoter such as ZrO 2 to enhance CO 2 adsorption and activation, controlling the concentration of CO and H 2 O to enhance methanol formation, and adopting a second catalytic component to enhance CO 2 conversion to other desired products such as olefins or aromatics on an acid catalyst such as zeolites. Through a comprehensive overview of the recent advances in In 2 O 3related catalysts, the present review paves the way for future development in In 2 O 3 -based selective catalysts for CO 2 hydrogenation to methanol.

Summary Kinetoplast DNA (kDNA), the trypanosome mitochondrial DNA, contains thousands of minicircles and dozens of maxicircles interlocked in a giant network. Remarkably, Trypanosoma brucei's genome encodes eight PIF1-like helicases, six of which are mitochondrial. We now show that TbPIF2 is essential for maxicircle replication. Maxicircle abundance is controlled by TbPIF2 level, as RNAi of this helicase caused maxicircle loss and its overexpression caused a 3- to 6-fold increase in maxicircle abundance. This regulation of maxicircle level is mediated by the TbHslVU protease. Previous experiments demonstrated that RNAi knockdown of TbHslVU dramatically increased abundance of minicircles and maxicircles, presumably because a positive regulator of their synthesis escaped proteolysis and allowed synthesis to continue. Here we found that TbPIF2 level increases following RNAi of the protease. Therefore this helicase is a TbHslVU substrate and the first example of a positive regulator, thus providing a molecular mechanism for controlling maxicircle replication.

Identifying the dynamic structure of heterogeneous catalysts is crucial for the rational design of new ones. In this contribution, the structural evolution of Fe(0) catalysts during CO 2 hydrogenation to hydrocarbons has been investigated by using several (quasi) in situ techniques. Upon initial reduction, Fe species are carburized to Fe 3 C and then to Fe 5 C 2 . The by-product of CO 2 hydrogenation, H 2 O, oxidizes the iron carbide to Fe 3 O 4 . The formation of Fe 3 O 4 @(Fe 5 C 2 +Fe 3 O 4 ) core-shell structure was observed at steady state, and the surface composition depends on the balance of oxidation and carburization, where water plays a key role in the oxidation. The performance of CO 2 hydrogenation was also correlated with the dynamic surface structure. Theoretical calculations and controll experiments reveal the interdependence between the phase transition and reactive environment. We also suggest a practical way to tune the competitive reactions to maintain an Fe 5 C 2 -rich surface for a desired C 2+ productivity.

Understanding the structure–catalytic activity relationship is crucial for developing new catalysts with desired performance. In this contribution, we report the performance of In2O3 with different crystal phases in the reverse water gas shift (RWGS) reaction, where we observe changing activity induced by a phase transition under reaction conditions. Cubic In2O3 (c-In2O3) exhibits a higher RWGS rate than the hexagonal phase (h-In2O3) at temperatures below 350 °C because of its (1) enhanced dissociative adsorption of H2, (2) facile formation of the oxygen vacancies, and (3) enhanced ability to adsorb and activate CO2 on the oxygen vacancies, as suggested both experimentally and computationally. Density functional theory results indicate that the surface oxygen arrangement on the cubic polymorph is key to rapid H2 adsorption, which facilitates oxygen vacancy formation and subsequent CO2 adsorption to yield high RWGS reactivity. At 450 °C and above, the activity of h-In2O3 increases gradually with time on stream, which is caused by a phase transition from h-In2O3 to c-In2O3. In situ X-ray diffraction experiments show that h-In2O3 is first reduced by H2 and subsequently oxidized by CO2 to c-In2O3. These findings highlight the importance of the crystal phase in the catalytic RWGS reaction and provide a new dimension for understanding/designing RWGS catalysts.

Introduced in the 1950s, ethidium bromide (EB) is still used as an anti-trypanosomal drug for African cattle although its mechanism of killing has been unclear and controversial. EB has long been known to cause loss of the mitochondrial genome, named kinetoplast DNA (kDNA), a giant network of interlocked minicircles and maxicircles. However, the existence of viable parasites lacking kDNA (dyskinetoplastic) led many to think that kDNA loss could not be the mechanism of killing. When recent studies indicated that kDNA is indeed essential in bloodstream trypanosomes and that dyskinetoplastic cells survive only if they have a compensating mutation in the nuclear genome, we investigated the effect of EB on kDNA and its replication. We here report some remarkable effects of EB. Using EM and other techniques, we found that binding of EB to network minicircles is low, probably because of their association with proteins that prevent helix unwinding. In contrast, covalently-closed minicircles that had been released from the network for replication bind EB extensively, causing them, after isolation, to become highly supertwisted and to develop regions of left-handed Z-DNA (without EB, these circles are fully relaxed). In vivo, EB causes helix distortion of free minicircles, preventing replication initiation and resulting in kDNA loss and cell death. Unexpectedly, EB also kills dyskinetoplastic trypanosomes, lacking kDNA, by inhibiting nuclear replication. Since the effect on kDNA occurs at a >10-fold lower EB concentration than that on nuclear DNA, we conclude that minicircle replication initiation is likely EB's most vulnerable target, but the effect on nuclear replication may also contribute to cell killing.