Deactivation of precious metal steam reforming catalysts

Steam reforming is a well established industrial process for the formation of synthesis gas. It takes place in two reversible stages: the reforming reaction (1) followed by the water-gas shift reaction (2). (1) CnH2n+2 + nH2O nCO + (2n+1)H2 (2) CO + H2O CO2 + H2 Reaction (1) is highly endothermic and is favoured at high temperatures and low pressure, while reaction (2) takes place at as low temperature as possible. One of the major problems affecting the steam reforming industry is catalyst deactivation due to sulphur poisoning. Sulphur is present in the hydrocarbon feedstock and even after desulphurisation steps some sulphur still remains, from ppb to ppm levels. Such low levels of sulphur can still poison the catalyst due to the catalyst having a significant time on stream. It is therefore desirable to produce a catalyst that exhibits sulphur resistance to prolong the lifetime of the catalyst. In this project the behaviour of precious metal catalysts (Rh and Pt supported on La-ZrO2, Al2O3 and SiO2) towards sulphur was examined. Two major aspects were studied, the catalysts’ adsorpitive behaviour towards sulphur and the effect of sulphur during the steam reforming reaction. Low pressure pulses of H2S and CH3SH over the catalysts followed by gas chromatography revealed that sulphur is a very strong adsorbing species, similar to CO, and could not be displaced by the adsorption of another species as there was no mechanism to desorb the sulphur species. The alumina supported catalysts offered some protection from sulphur poisoning, evidenced during co-adsorption experiments with CO, because the support was acting as a ‘sulphur sink’. Adsorption mechanisms were proposed for H2S at the different adsorption conditions tested: a 3-site adsorption mechanism producing surface sulphides at room temperature and at higher temperatures bulk sulphides were formed. High pressure steam reforming reactions of ethane were carried out at three different temperatures (600oC, 550oC and 500oC) to act as standards to the poisoned reactions, but also revealed interesting insights into the reforming of ethane. Each catalyst produced a unique reaction profile during steam reforming, with the La-ZrO2 catalyst exhibiting greatest activity. The Rh catalysts showed high selectivity towards the formation of CH4 due to the hydrogenolysis of C2H6, which was not occurring over the Pt catalysts. The Pt catalysts were the least active and deactivated considerably as the result of carbon formation. Sulphur species, hydrogen sulphide and methanthiol, were introduced into the reaction by dissolving them in the feed water. It was found the identity of the sulphur species had a significant impact upon the extent of catalyst deactivation, with methanthiol having the most detrimental effect, which was attributed to the molecule decomposing and laying down carbon. None of the catalysts tested exhibited particularly high sulphur resistance, particularly with regard to methanthiol, however Rh/ZrO2 did recover a lot of its original activity once the poison was removed from the feed. This was due to the removal of surface carbon rather than the removal of sulphur from the catalyst, because La-ZrO2 has a faster rate of oxygen transfer and therefore a mechanism to remove surface carbon

Identifying Transdiagnostic Mechanisms in Mental Health Using Computational Factor Modeling

Most psychiatric disorders do not occur in isolation, and most psychiatric symptom dimensions are not uniquely expressed within a single diagnostic category. Current treatments fail to work for around 25% to 40% of individuals, perhaps due at least in part to an overreliance on diagnostic categories in treatment development and allocation. In this review, we describe ongoing efforts in the field to surmount these challenges and precisely characterize psychiatric symptom dimensions using large-scale studies of unselected samples via remote, online, and "citizen science" efforts that take a dimensional, mechanistic approach. We discuss the importance that efforts to identify meaningful psychiatric dimensions be coupled with careful computational modeling to formally specify, test, and potentially falsify candidate mechanisms that underlie transdiagnostic symptom dimensions. We refer to this approach, i.e., where symptom dimensions are identified and validated against computationally well-defined neurocognitive processes, as computational factor modeling. We describe in detail some recent applications of this method to understand transdiagnostic cognitive processes that include model-based planning, metacognition, appetitive processing, and uncertainty estimation. In this context, we highlight how computational factor modeling has been used to identify specific associations between cognition and symptom dimensions and reveal previously obscured relationships, how findings generalize to smaller in-person clinical and nonclinical samples, and how the method is being adapted and optimized beyond its original instantiation. Crucially, we discuss next steps for this area of research, highlighting the value of more direct investigations of treatment response that bridge the gap between basic research and the clinic

Adsorption of hydrogen sulphide over rhodium/silica and rhodium/alumina at 293 and 873 K, with co-adsorption of carbon monoxide and hydrogen

In this study, we have examined the adsorption of hydrogen sulphide and carbon monoxide over rhodium/silica and rhodium/alumina catalysts. Adsorption of hydrogen sulphide was measured at 293 and 873 K and at 873 K in a 1:1 ratio with hydrogen. At 293 K, over Rh/silica, hydrogen sulphide adsorption capacity was similar to that of carbon monoxide; however, over Rh/alumina, the carbon monoxide adsorption capacity was higher, probably due to the formation of RhI(CO)2. Over Rh/silica, the primary adsorbed state was HS(ads), in contrast to Rh/alumina, where the H2:S ratio was 1:1 indicating that the adsorbed state was S(ads). Competitive adsorption between CO and H2S over Rh/silica and Rh/alumina revealed adsorption sites on the metal that only adsorbed carbon monoxide, only adsorbed hydrogen sulphide or could adsorb both species. At 873 K, hydrogen sulphide adsorption produced the bulk sulphide Rh2S3; however, when a 1:1 H2:H2S mixture was used formation of the bulk sulphide was inhibited and a reduced amount of hydrogen sulphide was adsorbed

Model-based learning protects against forming habits.

Studies in humans and rodents have suggested that behavior can at times be "goal-directed"-that is, planned, and purposeful-and at times "habitual"-that is, inflexible and automatically evoked by stimuli. This distinction is central to conceptions of pathological compulsion, as in drug abuse and obsessive-compulsive disorder. Evidence for the distinction has primarily come from outcome devaluation studies, in which the sensitivity of a previously learned behavior to motivational change is used to assay the dominance of habits versus goal-directed actions. However, little is known about how habits and goal-directed control arise. Specifically, in the present study we sought to reveal the trial-by-trial dynamics of instrumental learning that would promote, and protect against, developing habits. In two complementary experiments with independent samples, participants completed a sequential decision task that dissociated two computational-learning mechanisms, model-based and model-free. We then tested for habits by devaluing one of the rewards that had reinforced behavior. In each case, we found that individual differences in model-based learning predicted the participants' subsequent sensitivity to outcome devaluation, suggesting that an associative mechanism underlies a bias toward habit formation in healthy individuals.This work was funded by a Sir Henry Wellcome Postdoctoral Fellowship (101521/Z/12/Z) awarded to C.M.G. ND is supported by a Scholar Award from the McDonnell FoundationThe authors report no conflicts of interest and declare no competing financial interests.This is the final published version. It first appeared at http://link.springer.com/article/10.3758%2Fs13415-015-0347-6

Characterizing a psychiatric symptom dimension related to deficits in goal-directed control.

Prominent theories suggest that compulsive behaviors, characteristic of obsessive-compulsive disorder and addiction, are driven by shared deficits in goal-directed control, which confers vulnerability for developing rigid habits. However, recent studies have shown that deficient goal-directed control accompanies several disorders, including those without an obvious compulsive element. Reasoning that this lack of clinical specificity might reflect broader issues with psychiatric diagnostic categories, we investigated whether a dimensional approach would better delineate the clinical manifestations of goal-directed deficits. Using large-scale online assessment of psychiatric symptoms and neurocognitive performance in two independent general-population samples, we found that deficits in goal-directed control were most strongly associated with a symptom dimension comprising compulsive behavior and intrusive thought. This association was highly specific when compared to other non-compulsive aspects of psychopathology. These data showcase a powerful new methodology and highlight the potential of a dimensional, biologically-grounded approach to psychiatry research.Funded by a Sir Henry Wellcome Postdoctoral Fellowship (101521/Z/12/Z) awarded to CM Gillan. Claire M Gillan: Wellcome Trust 101521/Z/12/Z Nathaniel D Daw: National Institute on Drug Abuse 1R01DA038891 Nathaniel D Daw: James S. McDonnell Foundation Scholar AwardThis is the final version of the article. It first appeared from eLife Sciences Publications via http://dx.doi.org/10.7554/eLife.1130

Goal-Directed and Habitual Control in Smokers.

INTRODUCTION: Harmful behavior such as smoking may reflect a disturbance in the balance of goal-directed and habitual control. Animal models suggest that habitual control develops after prolonged substance use. In this study, we investigated whether smokers (N = 49) differ from controls (N = 46) in the regulation of goal-directed and habitual behavior. It was also investigated whether individual differences in nicotine dependence levels were associated with habitual responding. METHODS: We used two different multistage instrumental learning tasks that consist of an instrumental learning phase, subsequent outcome devaluation, and a testing phase to measure the balance between goal-directed and habitual responding. The testing phases of these tasks occurred after either appetitive versus avoidance instrumental learning. The appetitive versus aversive instrumental learning stages in the two different tasks modeled positive versus negative reinforcement, respectively. RESULTS: Smokers and nonsmoking controls did not differ on habitual versus goal-directed control in either task. Individual differences in nicotine dependence within the group of smokers, however, were positively associated with habitual responding after appetitive instrumental learning. This effect seems to be due to impaired stimulus-outcome learning, thereby hampering goal-directed task performance and tipping the balance to habitual responding. CONCLUSIONS: The current finding highlights the importance of individual differences within smokers. For future research, neuroimaging studies are suggested to further unravel the nature of the imbalance between goal-directed versus habitual control in severely dependent smokers by directly measuring activity in the corresponding brain systems. IMPLICATIONS: Goal-directed versus habitual behavior in substance use and addiction is highly debated. This study investigated goal-directed versus habitual control in smokers. The findings suggest that smokers do not differ from controls in goal-directed versus habitual control. Individual differences in nicotine dependence within smokers, however, were positively associated with habitual responding after appetitive instrumental learning. This effect seems to be due to impaired stimulus-outcome learning, thereby hampering goal-directed task performance and tipping the balance to habitual responding. These findings add to the ongoing debate on habitual versus goal-directed control in addiction and emphasize the importance of individual differences within smokers

The role of habit in compulsivity.

Compulsivity has been recently characterized as a manifestation of an imbalance between the brain׳s goal-directed and habit-learning systems. Habits are perhaps the most fundamental building block of animal learning, and it is therefore unsurprising that there are multiple ways in which the development and execution of habits can be promoted/discouraged. Delineating these neurocognitive routes may be critical to understanding if and how habits contribute to the many faces of compulsivity observed across a range of psychiatric disorders. In this review, we distinguish the contribution of excessive stimulus-response habit learning from that of deficient goal-directed control over action and response inhibition, and discuss the role of stress and anxiety as likely contributors to the transition from goal-directed action to habit. To this end, behavioural, pharmacological, neurobiological and clinical evidence are synthesised and a hypothesis is formulated to capture how habits fit into a model of compulsivity as a trans-diagnostic psychiatric trait.CM Gillan is supported by a Sir Henry Wellcome Postdoctoral Fellowship (101521/Z/12/Z).This is the final version of the article. It was first available from Elsevier via https://doi.org/10.1016/j.euroneuro.2015.12.03

Hyperconnectivity of the ventromedial prefrontal cortex in obsessive-compulsive disorder.

Neuroimaging research has highlighted maladaptive thalamo-cortico-striatal interactions in obsessive-compulsive disorder as well as a more general deficit in prefrontal functioning linked with compromised executive functioning. More specifically, dysfunction in the ventromedial prefrontal cortex, a central hub in coordinating flexible behaviour, is thought to be central to obsessive-compulsive disorder symptomatology. We sought to determine the intrinsic alterations of the ventromedial prefrontal cortex in obsessive-compulsive disorder employing resting-state functional connectivity magnetic resonance imaging analyses with a ventromedial prefrontal cortex seed region of interest. A total of 38 obsessive-compulsive disorder patients and 33 matched controls were included in our analyses. We found widespread ventromedial prefrontal cortex hyperconnectivity during rest in patients with obsessive-compulsive disorder, displaying increased connectivity with its own surrounding region in addition to hyperconnectivity with several areas along the thalamo-cortico-striatal loop: thalamus, caudate and frontal gyrus. Obsessive-compulsive disorder patients also exhibited increased functional connectivity from the ventromedial prefrontal cortex to temporal and occipital lobes, cerebellum and the motor cortex, reflecting ventromedial prefrontal cortex hyperconnectivity in large-scale brain networks. Furthermore, hyperconnectivity of the ventromedial prefrontal cortex and caudate correlated with obsessive-compulsive disorder symptomatology. Additionally, we used three key thalamo-cortico-striatal regions that were hyperconnected with our ventromedial prefrontal cortex seed as supplementary seed regions, revealing hypoconnectivity along the orbito- and lateral prefrontal cortex-striatal pathway. Taken together, these results confirm a central role of a hyperconnected ventromedial prefrontal cortex in obsessive-compulsive disorder, with a special role for maladaptive crosstalk with the caudate, and indications for hypoconnectivity along the lateral and orbito pathways

Carrots and sticks fail to change behavior in cocaine addiction.

Cocaine addiction is a major public health problem that is particularly difficult to treat. Without medically proven pharmacological treatments, interventions to change the maladaptive behavior of addicted individuals mainly rely on psychosocial approaches. Here we report on impairments in cocaine-addicted patients to act purposefully toward a given goal and on the influence of extended training on their behavior. When patients were rewarded for their behavior, prolonged training improved their response rate toward the goal but simultaneously rendered them insensitive to the consequences of their actions. By contrast, overtraining of avoidance behavior had no effect on patient performance. Our findings illustrate the ineffectiveness of punitive approaches and highlight the potential for interventions that focus on improving goal-directed behavior and implementing more desirable habits to replace habitual drug-taking.Sir Henry Wellcome Postdoctoral Fellowship (Grant ID: 101521/Z/12/Z)This is the author accepted manuscript. The final version is available from AAAS via http://dx.doi.org/10.1126/science.aaf370