Task SelectItemAsync( 
   Item Item,
   bool select,
   bool expand,
   Item container
)

//Get the catalog pane
ArcGIS.Desktop.Core.IProjectWindow projectWindow = Project.GetCatalogPane();
//or get the active catalog view...
//ArcGIS.Desktop.Core.IProjectWindow projectWindow = Project.GetActiveCatalogWindow();

//eg Find a toolbox in the project
string gpName = "Interacting with Maps.tbx";
var toolbox = Project.Current.GetItems<GeoprocessingProjectItem>().FirstOrDefault(tbx => tbx.Name == gpName);
//Select it under Toolboxes
projectWindow.SelectItemAsync(toolbox, true, true, null);//null selects it in the first container - optionally await
                                                         //Note: Project.Current.GetProjectItemContainer("GP") would get toolbox container...

//assume toolbox is also under Folders container. Select it under Folders instead of Toolboxes
var foldersContainer = Project.Current.ProjectItemContainers.First(c => c.Path == "FolderConnection");
//We must specify the container because Folders comes second (after Toolboxes)
projectWindow.SelectItemAsync(toolbox, true, true, foldersContainer);//optionally await

//Find a map and select it
var mapItem = Project.Current.GetItems<MapProjectItem>().FirstOrDefault(m => m.Name == "Map");
//Map only occurs under "Maps" so the container need not be specified
projectWindow.SelectItemAsync(mapItem, true, false, null);