Mechanocatalytic Synthesis of Ammonia: State of the Catalyst During Reaction and Deactivation Pathway.

Ammonia synthesis holds significant importance for both agricultural fertilizer production and emerging green energy applications. Here, we present a comprehensive characterization of a catalyst for mechanochemical ammonia synthesis, based on Cs-promoted Fe. The study sheds light on the catalyst's dynamic evolution under reaction conditions and the origin of deactivation. Initially, elemental Cs converts to CsH, followed by partial CsOH formation due to trace oxygen impurities on the surface of the Fe metal and the equipment. Concurrently, the mechanical milling process comminutes Fe, exposing fresh metallic Fe surfaces. This comminution correlates with an induction period observed during ammonia formation. Critical to the study, degradation of active Cs promoter species (CsH and CsNH2) into inactive CsOH emerged as the primary deactivation mechanism. By increasing the Cs content from 2.2 mol % to 4.2 mol %, we achieved stable, continuous ammonia synthesis for nearly 90 hours, showcasing one of the longest-running mechanocatalytic gas phase reactions. Studies of the temperature dependence of the reaction revealed negligible bulk temperature influence in the range of -10 °C to 100 °C, highlighting the dominance of mechanical action over bulk thermal effects. This study offers insights into the complex interplay between mechanical processing, reactive species, and deactivation mechanisms in mechanocatalytic ammonia synthesis.

Phylogenetic relationships of the Boana pulchella Group (Anura: Hylidae).

In this paper we present a phylogenetic analysis of the treefrogs of the Boana pulchella Group with the goals of (1) providing a rigorous test of its monophyly; (2) providing a test of relationships supported in previous studies; and (3) exploring the relationships of the several species not included in previous analyses. The analyses included>300 specimens of 37 of the 38 species currently included in the group, plus 36 outgroups, exemplars of the diversity of Boana and the other genera of the hylid tribe Cophomantini. The dataset included eight mitochondrial genes (12S, 16S, CytB, COI, ND1, tRNAIle, tRNALeu, and tRNAVal) and five nuclear genes (RHO, TYR, RAG-1, CXCR4, SIAH1). The phylogenetic analyses recover the monophyly of the B. pulchella Group with lower support than previous studies, as a result of the inclusion of the B. claresignata Group, which is recovered as its sister taxon. Within the B. pulchella Group, the inclusion of almost all species of the group had little impact on previous notions of its phylogeny, except for the rejection of the hypothesized B. polytaenia Clade (B. goiana and B. phaeopleura are nested in the clade here called the B. prasina Clade), which is redefined. Phylogenetic support is strong for five major clades, which collectively include all but three of the species sampled: the B. balzani Clade (B. aguilari, B. balzani, B. gladiator, B. melanopleura, B. palaestes), the redefined B. polytaenia Clade (B. botumirim, B. buriti, B. cipoensis, B. jaguariaivensis, B. leptolineata, B. polytaenia, B. stenocephala, and two undescribed species), the B. prasina Clade (B. bischoffi, B. caingua, B. cordobae, B. goiana, B. guentheri, B. marginata, B. phaeopleura, B. prasina, B. pulchella, and one undescribed species), the B. riojana Clade (B. callipleura, B. marianitae, B. riojana), and the B. semiguttata Clade (B. caipora, B. curupi, B. joaquini, B. poaju, B. semiguttata, B. stellae, and two undescribed species). The monophyly of the B. prasina + B. riojana Clades, and that of the B. polytaenia + B. semiguttata Clades are well-supported. The relationships among these two clades, the B. balzani Clade, B. ericae + B. freicanecae, and B. cambui (representing the deepest phylogenetic splits within the B. pulchella Group) are recovered with weak support. We discuss the phenotypic evidence supporting the monophyly of the B. pulchella Group, and the taxonomy of several species, identifying three new synonyms of Boana polytaenia, one new synonym of Boana goiana, and one new synonym of B. riojana.

In Situ Synchrotron X-ray Diffraction Studies of the Mechanochemical Synthesis of ZnS from its Elements.

Invited for the cover of this issue is Claudia Weidenthaler and co-workers at the Max-Planck-Institut für Kohlenforschung, Shenzhen University and Deutsches Elektronen Synchrotron. The image depicts the X-ray diffraction results showing the formation of ZnS and the subsequent phase transition from the hexagonal to the cubic modification. Read the full text of the article at 10.1002/chem.202101260.

In Situ Synchrotron X-ray Diffraction Studies of the Mechanochemical Synthesis of ZnS from its Elements.

Mechanochemistry, as a synthesis tool for inorganic materials, became an ever-growing field in material chemistry. The direct energy transfer by collision of the educts with the milling media gives the possibility to design environmental-friendly reactions. Nevertheless, the underlying process of energy transfer and hence the kinetics of mechanosynthesis remain unclear. Herein, we present in situ synchrotron X-ray diffraction studies coupled with pressure measurements performed during the formation of ZnS and the subsequent phase transition (PT) from the hexagonal to the cubic modification. Milling Zn and S8 results in the sublimation of S8 , observed by a sudden pressure increase. Simultaneously, the hexagonal metastable ZnS-modification (wurtzite) forms. Via detection of the pressure maximum, the exact start of the wurtzite formation can be determined. Immediately after the formation of wurtzite, the structural PT to the thermodynamic stable cubic modification sphalerite takes place. This PT can be described by the Prout-Tompkins equation for autocatalytic reactions, similar to thermally induced PT in sulfur vapor at high temperatures (T>1133 K). The increase in the reactivity of the wurtzite formation is explained by the reaction in sulfur vapor and the induction of defect structures by the collisions with the milling media.

Mechanocatalytic Room-Temperature Synthesis of Ammonia from Its Elements Down to Atmospheric Pressure.

Ammonia synthesis via the high-temperature and high-pressure Haber-Bosch process is one of the most important chemical processes in the world. In spite of numerous attempts over the last 100 years, continuous Haber-Bosch type ammonia synthesis at room-temperature had not been possible, yet. We report the development of a mechanocatalytic system operating continuously at room-temperature and at pressures down to 1 bar. With optimized experimental conditions, a cesium-promoted iron catalyst was shown to produce ammonia at concentrations of more than 0.2 vol. % for over 50 hours.

Phylogenetic relationships and systematics of the Amazonian poison frog genus Ameerega using ultraconserved genomic elements.

The Amazonian poison frog genus Ameerega is one of the largest yet most understudied of the brightly colored genera in the anuran family Dendrobatidae, with 30 described species ranging throughout tropical South America. Phylogenetic analyses of Ameerega are highly discordant, lacking consistency due to variation in data types and methods, and often with limited coverage of species diversity in the genus. Here, we present a comprehensive phylogenomic reconstruction of Ameerega, utilizing state-of-the-art sequence capture techniques and phylogenetic methods. We sequenced thousands of ultraconserved elements from over 100 tissue samples, representing almost every described Ameerega species, as well as undescribed cryptic diversity. We generated topologies using maximum likelihood and coalescent methods and compared the use of maximum likelihood and Bayesian methods for estimating divergence times. Our phylogenetic inference diverged strongly from those of previous studies, and we recommend steps to bring Ameerega taxonomy in line with the new phylogeny. We place several species in a phylogeny for the first time, as well as provide evidence for six potential candidate species. We estimate that Ameerega experienced a rapid radiation approximately 7-11 million years ago and that the ancestor of all Ameerega was likely an aposematic, montane species. This study underscores the utility of phylogenomic data in improving our understanding of the phylogeny of understudied clades and making novel inferences about their evolution.

A new species of Oxyrhopus Wagler, 1830 (Serpentes: Dipsadidae) from the Bolivian Andes.

We describe a new dipsadine snake species, of the genus Oxyrhopus Wagler, 1830, from the highlands of Bolivia. Oxyrhopus emberti sp. n. is diagnosed from its congeners based on external and hemipenial morphology. The new species inhabits the humid forests of Yungas and Tucumano-Bolivian Forest highlands, between 1.200 - 1.800 meters above sea level, and is likely to be a Bolivian endemic. We also discuss the relationships of the new species with Andean congeners and provide a key to the identification of the Oxyrhopus species from the Central Andes of Bolivia and Peru.

In situ synchrotron x-ray diffraction studies monitoring mechanochemical reactions of hard materials: Challenges and limitations.

In situ monitoring of mechanochemical reactions of soft matter is feasible by synchrotron diffraction experiments. However, so far, reactions of hard materials in existing polymer milling vessels failed due to insufficient energy input. In this study, we present the development of a suitable setup for in situ diffraction experiments at a synchrotron facility. The mechanochemical transformation of boehmite, γ-AlOOH, to corundum, α-Al2O3, was chosen as a model system. The modifications of the mill's clamping system and the vessels themselves were investigated separately. Starting from a commercially available Retsch MM 400 shaker mill, the influence of the geometrical adaptation of the setup on the milling process was investigated. Simply extending the specimen holder proved to be not sufficient because changes in mechanical forces need to be accounted for in the construction of optimized extensions. Milling vessels that are suitable for diffraction experiments and also guarantee the required energy input as well as mechanical stability were developed. The vessels consist of a steel body and modular polymer/steel rings as x-ray transparent windows. In addition, the vessels are equipped with a gas inlet and outlet system that is connectable to a gas analytics setup. Based on the respective modifications, the transformation of boehmite to corundum could be observed in an optimized setup.

The tadpole of Ameerega boehmei in southeastern Bolivia.

To date, half (16 of 32) of the species of Ameerega have had their tadpoles described: A. altamazonica, A. bassleri, A. bilinguis, A. braccata, A. cainarachi, A. flavopicta, A. hahneli, A. macero, A. parvula, A. petersi, A. picta, A. rubriventris, A shihuemoy. A. silverstonei, A. smaragdina, and A. trivittata (Lescure, 1976; Silverstone, 1976; Duellman, 1978; Myers Daly, 1979; Rodriguez Myers, 1993; Haddad Martins, 1994; Lötters et al., 1997; Duellman, 2005; Costa et al., 2006; Twomey Brown, 2008; Brown Twomey, 2009; Poelman et al., 2010; Schulze et al., 2015). Ameerega boehmei is a putative member of a clade containing Ameerega braccata, A. flavopicta, A. berohoka, A. munduruku, all of which inhabit various parts of the 'dry diagonal' between the Amazon and Atlantic rainforests (Prado Gibbs, 1993). Adult frogs in this group are morphologically similar, generally dark-bodied with yellow dorsolateral stripes, orange flash marks and some also possessing bright-yellow dorsal spots. Despite considerable research on their breeding behavior, acoustics and systematics (Lötters et al., 2009; Forti et al., 2013), the tadpole of Ameerega boehmei, the southern-most and western-most distributed species in this tentative group, has not been described.

The influence of climatic seasonality on the diversity of different tropical pollinator groups.

Tropical South America is rich in different groups of pollinators, but the biotic and abiotic factors determining the geographical distribution of their species richness are poorly understood. We analyzed the species richness of three groups of pollinators (bees and wasps, butterflies, hummingbirds) in six tropical forests in the Bolivian lowlands along a gradient of climatic seasonality and precipitation ranging from 410 mm to 6250 mm. At each site, we sampled the three pollinator groups and their food plants twice for 16 days in both the dry and rainy seasons. The richness of the pollinator groups was related to climatic factors by linear regressions. Differences in species numbers between pollinator groups were analyzed by Wilcoxon tests for matched pairs and the proportion in species numbers between pollinator groups by correlation analyses. Species richness of hummingbirds was most closely correlated to the continuous availability of food, that of bees and wasps to the number of food plant species and flowers, and that of butterflies to air temperature. Only the species number of butterflies differed significantly between seasons. We were not able to find shifts in the proportion of species numbers of the different groups of pollinators along the study gradient. Thus, we conclude that the diversity of pollinator guilds is determined by group-specific factors and that the constant proportions in species numbers of the different pollinator groups constitute a general pattern.